Gemology

INTRODUCTION TO GEMOLOGY By Barbara Smigel, PhD, GG.

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LESSON 1: BASIC TERMS What is a gem? Although you might not be able to give a precise definition of a gem at this time, few of you would have any trouble in recognizing that the images below are of gems. So then, what characteristics do they exhibit that allow you to intuitively recognize them, and cause gemologists or geologists to officially label them as such?

[Cabochon and carved gems, faceted gems] A gem is a natural, mineral or organic substance, that has substantial beauty, rarity, and durability. Let's take each underlined part of that definition and examine it: Natural means that the material was not made, or assisted in its making, by human effort. When such is the case, modifiers such as "laboratory grown", "synthetic", "cultured", or "man-made", must, by Federal Trade Commission (FTC) regulations, be used in the descriptions of any such pieces being advertised or marketed. Man-made "gems" have all the chemical, optical and physical characteristics of the natural materials they imitate, but they do not have their rarity or value. You can be certain whenever you see any of the above modifiers that the material in question is notof natural origin. A mineral can be defined as a crystalline solid with a specific chemical formula, and a regular three dimensional arrangement of atoms. (In a later web lecture, this definition will be broadened to include "amorphous" materials which have a specific chemical formula but do not have a specific crystalline structure, for example, opal and natural types of glass). Mineral Gems Iolite, which has a specific chemical formula of: Mg2Al4Si5O18 and a regular arrangement of atoms which places it into a crystal system, with other 2

minerals of similar structure, known as the orthorhombic crystal system is a mineral gem. Another example is emerald, Be3Al2(SiO3)6, a member of the hexagonal crystal system. (The attributes of the various crystal systems will be presented in an upcoming lesson.) **Check the text: For a preview of crystal systems see page 19 in the Hall text.

[Faceted iolite, uncut emerald crystal] Organic Gems An organic gem is one that was made by living things, present or past. Examples include pearls, coral, jet, ivory, shell and amber. Such gems consist of the molecules formed by the organism, although these molecules may have beem altered somewhat due to compression or other geological or chemical forces.

[Organic gems: coral and freshwater cultured pearl earrings, faceted amber (enlargement showing fossilized insect within the gem] **Gems such as "petrified dinosaur bone" and many other "stony" fossil gems, are classified as mineral, rather than organic. Although its true that bone is an organic material: the reasoning involved is that the original organic molecules and structures of long ago have beentotally replaced with mineral solutions such as silica. (This common geological process is called petrifaction).**

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[Not classed as organic gems: petrified dinosaur bone agate, cabochon cut from a fossilized coral colony] Although none of the molecules from the living organisms remain in certain types of organic gems, such as the calcareous corals, the minerals they are composed of were secreted, originally, by the living things as they grew, not replaced later by petrifaction. Likewise, although substantial geologic changes have altered the properties of jet and amber, the materials still consist primarily of the original organic molecules.

[Classed as organic: calcareous "angel skin" coral carved beads, carved jet earrings, circa 1925 amber and jet cigarette holder: Image courtesy of www.fraleigh.ca] A gem is beautiful. Beauty, of course, is a subjective concept that has many aspects, and differs from viewer to viewer, but in general, the attributes of gems which excite our sense of beauty include, color, transparency, luster, brilliance, pattern, optical phenomena and, in some cases, distinctive inclusions.

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[Kunzite: color, transparency, brilliance, jasper: color, pattern, luster]

[Ammolite: color, luster, iridescence (an optical phenomenon), rutilated quartz: transparency, distinctive inclusions] A gem is rare. There are two types of rarity involved: relative and inherent. Relative: Many gem minerals occur in various locales and, often, in large deposits, but the vast majority of the material does not approach "gem quality". Inherent: Other minerals occur in only a few locations or in very small deposits. Inherently rare gems are doubly rare as the fraction of an already small amount of ore which is gem quality is very, very, small indeed.

[Ruby: a gem with relative rarity, Benitoite: a gem with inherent rarity] The mineral corundum (of which ruby is a gem example) is widespread and abundant. So much so, that an enormous amount of low grade corundum is used in industry for abrasives, due to its hardness (9 on a scale of 10). [Interestingly, very tiny, non-gem grade, corundum crystals have found

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use in today's beauty industry-->as the active ingredient in both medical "dermabrasion"agents, and over the counter "exfoliating" products.]

["Specimen" grade corundum $50 per pound (= @ 2 cents per carat): Image courtesy of Las Vegas Jewerly and Mineral] Benitoite, on the other hand, is found in gem quality in only one location on Earth: the San Benito River Valley in California. Only a few ounces of cut gems result from each year's mining efforts, almost all of which are quite small in size. Ironically, this ultra-rare, nearly unobtainable stone has been officially designated as the State Gemstone of California.

[Pyramid of gem rarity] Usually in a deposit of gem mineral bearing ore, the majority is not the mineral being sought. From the small portion of the ore which bears the gem mineral, the majority is too low grade to have any gem uses. For example,

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80% of the diamond recovered from diamond bearing ore, is industrial grade. Within the small amount of gem grade material, the bulk of it is of lowest quality and useable only for inexpensive beads or trinkets. The even smaller amount of better material which can be extracted, is mostly middle grade, or that which is used for cabochons and better beads and carvings. A tiny fraction is high grade and can be used for faceting. Most of the facet grade material has some defects in color or clarity that limit it to "commercial" quality gems. Only the most miniscule part of the original deposit is top grade: AAA color and flawless clarity. Because the starting amount at the base of the pyramid for a gem like ruby is much larger than the starting amount for a gem like Benitoite, the amount at the top is correspondingly larger. Finally, picture taking that top "highest grade" part of the pyramid and dividing it, again, into layers based on size: from small at the base, to large at the tip. Is it any wonder that the largest, finest gems bring astronomical prices? Check the web: To view a list of the World's ten rarest gemstones, visit this site: http://www.curiousnotions.com/home/gemstones.html Speaking of prices: How valuable are gemstones? If you ask people at random to name a valuable commodity, many might say gold. And true, we do think of gold as valuable. Consider this: • • •

Good quality amethyst gems sell for about $40/ct Fine quality aquamarine sells for around $200/ct Highest gem quality blue sapphire sells for as much as $2500/ct.

Pure gold, however, is worth well under $10 per carat! Down through the centuries, gemstones have respresented the ultimate in portable wealth. (In the next lesson, we'll go through the calculation that produced the cost of gold figure). A gem is durable. It must be strong enough to withstand the stresses and forces involved in fashioning it, and its subsequent use as an ornamental object, or in jewelry. Most everyone has heard of "hardness" and knows that harder is better, in terms of using gems for jewelry--> but in reality, 7

hardness is only the beginning of the story. There are two other aspects of gem durability that are at least as important as hardness. Three Aspects of Durability 1) Hardness is the ability to resist scratching. Commonly measured on the "Mohs" Scale of 1 - 10. Talc lowest (1), diamond highest (10). Soft gems, especially those below 7 will tend to become dull through abrasion with harder materials in the environment, and lose their surface polish and their crisp edges over time. 2) Toughness is the ability to resist breaking or chipping. This property is measured in relative terms rather than on a numeric scale: sphalerite is fragile, diamond is moderately tough and jade is exceptionally tough. The lower the toughness of a gem the more susceptible it is to damage by the kinds of blows and knocks that are inevitable with frequent wear and use. 3) Stabilty is resistance to changes caused by environmental factors such as temperature, chemicals and light. Apatite is temperature sensitive, pearls are chemically sensitive, and Kunzite's color is unstable in strong light. Unstable gems exposed to common factors of the natural or man-made environment are likely to break, change color, or lose their luster. Food for thought: Taking into account each of the aspects of the definition of a gem, explain why is each of these not a gem.(Answers to the question are found at the end of the lesson.) Question One: An exotic butterfly wing, an industrial grade natural diamond, quartz beach sand, a laboratory grown ruby.

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LESSON 2: NAMING GEMS AND MEASURING GEMS: Naming Gems: Similarly to the way organisms are named in biology, in gemology, each distinct type of gem has a species name. Species: A gem species is a mineral that has a definite chemical formula, and has a particular three dimensional structure. In regards to that structure, gems can have a crystalline (highly regular and organized), or amorphous (less organized) structure. An example of a gem species is quartz. All quartzes, whatever their other characteristics, share the same chemical formula: SiO2 and are members of the hexagonal crystal system. (We'll be looking at the characteristics of the various crystal systems in a later lesson). The species "quartz" encompasses many quite different looking gems, though, from amethyst and citrine, to agate and jasper, to rutilated quartz and tiger'seye. Another example of a gem species is corundum (commonly known as sapphire). All corundum gems share the chemical formula: Al2O3 and are members of the trigonal crystal system. Variety: A gem variety is composed of a sub-group, within the species, that shares distinct and notable characteristics, such as color, degree of transparency, inclusions, or optical phenomena with others of its kind. Not every gem species has multiple varieties, for example, there are no separate varieties within the gem species peridot. Quartz Gems:

[Species quartz: Varieties: amethyst, agate] Amethyst is transparent, crystalline, purple quartz. Agate is translucent, usually banded or patterned, cryptocrystalline (made of ultra-microscopic crystals in an aggregate) quartz. Amethysts come in a range of purple colors 9

from very light to dark, and agates come in a nearly infinite array of colors and patterns. Corundum Gems:

[Species corundum: Varieties: ruby, yellow sapphire, star sapphire] Ruby is the variety name for red corundum, yellow sapphire is yellow corundum and star sapphire is translucent to opaque corundum that shows the optical phenomenon of asterism (forms a star figure from reflected light). The only variety of corundum that is simply called "sapphire" without any modifier is blue sapphire, all other colors have their own variety name (like ruby) or use a modifier like star, yellow, pink, white, etc. Groups: In some cases, a number of closely related mineral species are placed into a larger, more inclusive category, called a mineral group. Examples are the garnet group and the feldspar group. The individual species of the group share membership in the same crystal system, but although the chemical formulas amongst group members are very similar, they are not exactly the same throughout the group. Typically, the formulas gradually change by substitution of a set of chemical elements from one end of a continuum to the other. Garnet Group: All garnets, whatever their individual species and varietal designations, are members of the isometric crystal system and are metallic silicate minerals with various proportions of Ca, Fe, Mg, Al, Cr and Mn substituting for each other within a similar chemical formula. (To amplify: the generic formula for any garnet is A 3B 2Si 3O12 where the "A" position can be occupied by iron, calcium, manganese or magnesium, and the "B" position can be occupied by aluminum, iron, titanium or chromium. The rest of the formula is standard for all gems known as garnets). Garnet Group Gems: 10

[Group: garnet, Species: Spessartite, Group: garnet, Species: grossularite, variety: Tsavorite] The orange oval stone above belongs to the Spessartite* species within the garnet group. (Spessartites are manganese rich), and no individual varieties are designated within this species. The green stones above belong to the calcium rich grossularite species within the garnet group. There are several named varieties of grossularites, including medium to dark green stones colored by trace amounts of chromium and vanadium, called Tsavorite. * *When species or variety names come from proper nouns such as those designating a person (like Kunzite, named for G. F. Kunz, or Spessartite, named after the type location, Spessart in Germany), they are capitalized. Otherwise lower case is used, as in grossularite, agate and amethyst. Trade Names and Misnomers: In addition to the official names given to gems, there are also a multitude of trade names, brand names, and misnomers that are in use. In fact, just as happened in the history of biology, the confusion over which mineral or gem was called what, where, by whom, has led to the development of a rigorous system for international naming of minerals and gems. Although this formal system is used by professionals, students, and serious gem enthusiasts among the public, many other names are still in use and can create confusion. Trade Names: In modern times, trade names have most often developed when a new gem material is first discovered and marketed, as a way to "romance the stone". Let's say you are in Tanzania and you mine a facetable, but insipid looking light brown, transparent form of the mineral zoisite. You discover that heat treating will turn it to a gorgeous blue-violet color. The correct descriptive term would be: heated brown zoisite.

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Who would rush out to buy that? But, what if you call this gem something exotic and evocative of its foreign mine site, like "Tanzanite"--> now you something more marketable!

[Heated brown zoisite = Tanzanite] Sometimes, what starts out as a trade name becomes so widely used that it is essentially adopted as the official name. Exactly this has happened in the case of Tanzanite. Other examples of names which started out as marketing ploys and ended up on the officially sanctioned list include: "Kunzite" for pink spodumene, named for the famous early 20th century gem explorer and writer, G. F. Kunz and, "Tsavorite" for green grossular garnet named for its original mine locale (Tsavo National Park in Kenya).

[Kunzite, Tsavorite] This strategy doesn't always work, and intended trade names sometimes fail. There are numerous examples in which trade names were used for a period of time, or by a specific seller, but then either died out, or never became widespread. An aggressive campaign to present heated blue zircon as "Starlite" failed, as did a similar effort to label high grade sugilite as "Royal Azel".

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[Still just blue zircon and gem grade sugilite] The jury is still out on some: The relatively recent gem discovery, blue pectolite, which occurs only in the Dominican Republic in one location, has been promoted vigorously as "Larimar"--> named by the mine owner for a conjuction of his daughter's name and the local word for "sea". At this point the general consensus seems to be in favor of this lovely name. Within the last few years a deposit of strikingly marked purple and white opalized fluorite has been sold as "Picasso Stone" among other creative trade names. Although you still see this and various other terms in use, most folks in the gem world seem to be sticking with the more mineralogically descriptive name, opalized fluorite.

[Blue pectolite or "Larimar"?, "Picasso stone" or opalized fluorite?--> not finally decided yet!] Brand Names: Brand names usually develop when a seller is trying to differentiate their product from other identical or very similar ones. A case in point--> each of the two major home shopping channels sells its own brand named version of the diamond simulant cubic zirconia. QVC sells it as "DiamoniqueTM" and HSN as "AbsoluteTM". Cubic zirconia, or CZ, is widely sold under its generic name at lower prices, so here, the name becomes a way of "branding" that creates "added value" in the marketplace. We are all quite familiar with this concept in the marketing of common food staples like catsup and mayonnaise, but it is every bit as effective a device in selling gems and jewelry.

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[AbsoluteTM, DiamoniqueTM or plain old CZ?: depends on the seller] Misnomers: A misnomer is a wrong, or false, name. Often misnomers are folk names, from ages past, that have persisted into modern times. Sometimes they are used out of ignorance, but sometimes, unfortunately, they are used to deceive.

[Misnomers: "smoky topaz", for smoky quartz, "white turquoise" for howlite] One of the few vintage misnomers that can still occasionally be heard, even among modern day jewelers, and reputable gem dealers, is "smoky topaz". For many years this name was used incorrectly for the gem smoky quartz. Probably, it started out innocently enough, as many such names do, as a language translation failure, or an inability to correctly identify the species. Its use grew, however, even after the true identity was established, due primarily to the profit motive. Topaz is a generally more valuable gem than quartz, so by calling this variety of quartz by the topaz misnomer, it could sometimes be sold at higher prices to the unwary. In their defense, individuals from earlier centuries who searched for, and traded in gems, did not have the gemological knowledge or instruments necessary to make the exacting identifications of today. Usually the location, color, and some simple physical characteristics like hardness, luster, crystal habit, and cleavage were the only basis for naming, and many incorrect identifications were made. 14

Examples can be seen in the misidentification of some of the famous gems of history, such as Cleopatra's emeralds (which were probably peridots). Or as in the case of the "Black Prince's Ruby" in the Crown Jewels of England, which turned out, upon testing, to be a spinel.

[Green rough stones, collected circa 1900 from the now exhausted St. Johns Island mine in Egypt, legendary home of Cleopatra's "emeralds": the gems are, in fact, peridot: Image courtesy of www.irocks.com] Additionally, the folk name of a gem in one language may not have translated exactly, and may have innocently acquired new shades of meaning as the goods changed hands in international commerce. Lists of such misnomers and folknames fill databases with thousands of items, many of which can still be found in use in various locations. Hopefully, as the level of gemological education and sophistication among both buyers and sellers grows, the majority of such terms will slowly drop out of circulation. Misnomer/Folk Name Balas Ruby Transvaal Jade Mexican Onyx Swiss Lapis Black Hills Ruby New Jade

Correct Name Red Spinel Translucent Green Hydrogrossular Garnet Banded Calcite Marble Dyed Blue Chalcedony or Jasper Pyrope Garnet Bowenite or Serpentine

You can see from this short list that when a gem name that consists of a "modifier" in front of a recognized gem species or variety name, it is likely to be a misnomer. The material is most probably something else, not the gem (ruby, jade, lapis, etc.)-->usually something less valuable but with 15

superficially similar characteristics. (Remember the distinction between a simulant and fake from Lesson 1: serpentine sold as faux jade or imitation jade is a simulant, serpentine sold as New Jade (which implies it is really a type of jade) is a fake, and the name is a misnomer.) In today's competitive world of marketing gems, misnomers are making something of a comeback. An example which can commonly be seen on TV shopping channels, in mail order catalogues, at flea markets, and even in retail stores is the term "white turquoise" for the mineral howlite, which is a creamy white with veins of darker color running through it. Gemologically, turquoise is defined by the presence of the copper in its chemical makeup. The copper content invariably gives it some shade of blue or green. So "white turquoise" is not only a misnomer, but an oxymoron as well. Don't feel like a dummy if you find that you've purchased something sold under a misnomer. It can happen to anyone--> here's a picture of a "smoky topaz" ring I bought from a well known retail jewelry chain, years before I became a gemologist. I still like it and wear it, even though I now know it's quartz and I paid way too much money for it. :-)

[Your instructor's "smoky topaz" ring] Check the web: This website has an authoritative and amusing list of gem misnomers: http://www.thegemdoctor.com/misnomers.html Weighing Gems: In the early history of gem marketing, depending on the geographic location, one of two common items, familiar to both buyers and sellers, was used to measure the amount of gem material being bought and sold: the wheat grain and the carob seed. Each of these commodities was known for being particularly uniform in size and weight. We still see remnants of this early system in today's terms: "carat" the international metric unit used for gems, and "grain" a unit sometimes used in selling pearls, and also in today's system of apothecary measure. **As we work through this section, you'll probably begin to wonder why it's all so complicated, confusing and haphazard seeming. Unfortunately, the system 16

in place today developed bit by bit from mergers and splits amongst pre-existing local systems. The, sometimes frustrating, result is pretty much of a hodgepodge. Although some degree of uniformity has been introduced by the use of the metric system, things still are far from predictable and totally logical. Carat: The carat, pronounced like the vegetable, carrot, and abbreviated "ct" is 0.2 grams. So, there are five carats per gram. The metric system is the basic international standard used for gem commerce. Many of us who live in the US or UK where English measure is more common, need to take time, and do some practice, in order to get a "feel" for carats, grams, etc. The ounce, a familiar English unit of weight, equals approximately 142 cts. So, there really isn't an appropriately small unit in the English system which could be easily applied to gem weights. [To illustrate: a 1 ct. gem weighs 0.007 oz.] Another oddity of the US system is our use of the term "karat", also pronounced like the vegetable carrot, but abbreviated "k" or "kt" to indicate the fineness (purity) of gold. In most other countries, the purity of gold is indicated by the number of parts of gold out of 1000, such as 585 or 750, so there is no chance of confusion with gem weights. The number 585 means that 585 out of 1000 parts of the alloy are gold or, in other words, that the gold content is 58.5%. In comparison, the karat system uses the number of parts out of 24 that are gold. 24k means 24/24th, pure gold, also known as "fine" gold, 18k gold = 18/24th gold, and 14k = 14/24th gold. (14k and 18k and 24k translate then, in the International system, to 585, 750 and 999 respectively). **Check the text: See Lyman, pg. 41. The authors (who are Italian and can be forgiven because as Europeans they don't use the karat system, mistakenly use the word "carat" instead of "karat" in describing how gold is marked in the US, and Lyman, the American editor, didn't catch it. So, don't you be confused: For gems it's carat, for gold it's karat !!

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[Stamp on a 24k or "fine" gold piece] The time honored way that jewelers and gold dealers tested gold purity was by using acids and a set of test needles of known karatage. A streak was made by the object being tested on a stone plate and comparison streaks made below it with the test needles. Then the acid solution was applied to all. Based on the degree and color of the reaction, compared to the test streak reactions, the composition could be closely approximated. We get our terms "touchstone" and "acid test" from this ancient procedure. Kits using this same principle are sold, and still widely used today, although a newer system based on electrical conductivity is becoming popular. In devices of this newer type the test object is immersed in a few drops of electrolyte solution, and then subjected to a current--> its purity level can then be read directly from the scale.

["Acid Test" kit, electronic gold tester: images courtesy of Prettyrock.com] Getting to know the carat:

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Below, you see the carat weights of three common objects: since you are likely to be familiar with their approximate weights, this can perhaps help you begin to get a "feel" for the weights represented in carats. Common items weighed in carats:

[Small, (1.5" x 2.0") Post-it note = .75 ct., standard bobby pin = 2.8 ct., dime = 11 ct.] Special Cases: Pearls Pearl Grain: The pearl grain, is .25 grams, so one gram is equal to 4 pearl grains. Thankfully, the only remaining use of this once important measure, is sometimes seen in the sale of natural pearls by weight. Because there is very little commerce today in natural pearls (virtually all pearls on the market are cultured), it is fast becoming obsolete. Many cultured pearl wholesalers still sell bundles of pearls in larger units called "momme" which, historically, weighed 75 pearl grains. Cultured pearls are sold by diameter (millimeters) if they are round, or near round, and by carat if they are oddly shaped (baroque).

[9 mm. round cultured pearl, 8.4 ct. baroque cultured pearl]

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Check the web: The folks at pearl-guide.com have (among articles on just about any aspect of pearls you'd like to learn about), a short and clear web page explaining pearl weights: http://www.pearl-guide.com/pearl-weights.shtml Melee & Total Weight Melee: Gems weighing .20 ct. or less are referred to by the gem trade as "melee". They are most often not sold by weight, but rather by girdle diameter: 2 mm., 3.5 mm., etc. Such stones are generally used as accents, for cluster settings, or in pave' work. Total weight: When a jewelry piece has more than one stone, such as a center stone and accents, the total carat weight, must be used: abbreviated as "ct. tw."

[Ring with diamonds and Tsavorite pave' melee of .70 ct. tw., pendant with rubellite tourmaline and diamonds: .66 ct. tw.] Big Items Gem rough, and in some cases, carvings and ornamental objects are sold by the gram, (gr) or kilogram, (kg) as the carat is an inappropriately small unit for such goods. Occasionally, you see such wares with simply a per piece price without any weight measure listed at all.

[57.5 gr. ruby in zoisite gem carving ] 20

Metals Metals, like gold, platinum and silver, are not weighed in the metric system of carats and grams, nor the English system of ounces and pounds, but in the "Troy" system. Unfortunately, the Troy system also uses the terms "ounce" and "pound" but these terms are not equivalent between systems. When you hear that gold is selling at $900 per ounce, it is a Troy ounce which is about 10% heavier than an "English" ounce. (An English ounce = ~ 142 ct. whereas a Troy ounce = ~ 156 ct.) Troy ounces are subdivided into smaller units called pennyweights, abbreviated "dwt.". There are 20 dwt./ troy oz. Jewelers generally buy their gold casting grain, by the pennyweight. To further complicate matters, there are 12 Troy ounces in a Troy pound rather than 16 oz/lb as in the English system! Remember, in the last web lecture, gold was said to be worth substantially less than $10.00/ct.? We can now see how that figure was calculated: gold at $900 per ounce (Troy) = $900 per 156/ct., so dividing 156 into $900 gives us $5.77/ct. Check the current price to get a more accurate figure. Check the web: This website tracks gold prices minute to minute: http://goldinfo.net/gold1.html Food for thought: Presuming you want the most gold possible: (Answers to the questions are found at the end of the lesson.) Question One: Would you rather have a Troy ounce of gold or an English ounce? Question Two: Would you rather have a Troy pound of gold or an English pound of gold? Precision In commerce, colored stones are generally weighed to 0.1 ct. and diamonds are usually weighed to .01 ct. Each 1/100th of a carat is called a "point". So, one could alternately describe a 0.50 ct. diamond as weighing 50 points. {Interestingly, in the world of diamond sales, 50 points is not precisely the same as "1/2 carat".Fractional parts of carats actually refer to ranges! It is legal and proper to advertize and sell to any diamond within the range of 0.45 ct to 0.55 ct. as a 1/2 carat stone. Tools for Weighing 21

Long ago, gems and precious metals were weighed for trade by using simple hand held or platform mounted pan balances. The dealer placed the requisite number of carob seeds or wheat grains (common items with very standard weights) in one pan and added gems or gold in the other pan until the two pans hung level. Although this sounds primitive, a practiced user can get very accurate weights, and such tools are still in use in much of the world, although carob seeds have been replaced by tiny, carefully calibrated metal "weight standards" marked in carats or grams.

[Antique brass pan balances] Several decades ago, mechanical spring balances or beam balances were state of the art, today, however, virtually all gems are weighed on electronic scales. The basic principle is the same as that of the spring or tension balance (like the kind you weigh produce in at the grocery store). The difference is that the pressure from the object being weighed, instead of stretching or compressing a spring, creates increased electrical resistance. The result is displayed digitally as the object's weight.

[Electronic carat scale] 22

Factors affecting weight: It might seem, at first thought, that all 6 millimeter round gems would weigh about the same, but there are two important factors which greatly affect individual gem weight: 1) the density of the material (its weight per unit), and 2) the proportions of the cut. In the next lesson we'll learn more about gem density (specific gravity) but the basic idea is that some gem species weigh more per unit than others, just like a 4" cube of steel will weigh more than a 4" cube of oak. (Sapphire, for example, has a higher density than quartz, so a 6 millimeter round sapphire, all other factors being equal, would weigh more than a 6 millimeter round quartz.) The cut, particularly in regards to the pavilion depth and degree of pavilion bulge, is equally important in determining the weight of any given gem of a certain length and width. The diagram below shows two gems of the same face up dimensions, let's say 6 millimeter rounds, but which are cut to very different proportions. The deep or "belly" cut gem weighs much more, both due to the greater depth of the pavilion and to the bulging out of the sides. It is quite common to find "native cut" gems of this type. This is partly because the lapidaries in the country of origin are frequently paid by weight, but also because such gems, though awkward to mount in standard Western commercial settings, deepen the apparent color of lighter gem materials. (There is more to come about cut in Lesson 7).

[The effect of cut on gem weight: Image courtesy of www.tripps.com] Measuring Gems

The common household ruler, generally has inches on one side and millimeters on the other side. It's a good item to keep handy when first attempting to get a feel for metric gem measurements. If you saw a description of a gem that says it measures 8 x 10 millimeters, that might not 23

bring up an immediate mental picture of its size. Using your ruler, it's pretty easy to make a small sketch to represent the gem. Doing this a few times is all that's necessary to begin to think more easily in millimeter sizes. Such a ruler isn't precise enough for jewelers or gem dealers, who have a variety of moderately to extremely accurate measuring devices at their disposal. The simplest, least expensive, and most portable of these is the engraved brass sliding pocket gauge, seen below. The gem is placed between the jaws which are gently slid into contact with it. The lower scale generally reads in millimeters and the upper scale in inches. For greater precision there are several other options to choose from, such as the screw micrometer and the digital sliding gauge.

[Brass sliding gauge]

[Digital sliding gauge] With the simple brass sliding gauge accuracy is to tenths of millimeters, hundredths of millimeters must be estimated, not so with the digital version.

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A specialized type of jeweler's measurement tool, which has great versatility, is called the Leveridge gauge, available in both mechanical (seen below) and electronic types. Besides measuring loose gems, this device is useful in taking certain measurements on gems already set into jewelry. This can be done directly if the setting is open on the bottom--> one prong goes on the gem's table and the other on its culet or keel. In addition, the pointed jaws opposite the prongs, can be used to get pretty good estimates of distances, even if the setting is closed.

[Leveridge gauge: Image courtesy of www.riogrande.com] Also favored by jewelers are stone and hole gauges, which can be used to get fairly accurate estimates of the dimensions of a given gem, or the size of a particular opening on a setting.

[Stone gauge, stone and hole gauge: Images courtesy of www.riogrande.com] Where to Measure ?

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Having a good tool is necessary, but you also need to know the appropriate place to take each measurement. Length and width are the two primary dimensions of interest, although in the formal cut grading system for gems a large group of other measurements are taken, such as table width, total depth, crown height, etc. Each of the regular shapes of gemstones has a preferred position for taking length and width measures. Most are pretty obvious (the two longest perpendicular dimensions), but the special situation of the heart shape bears mentioning. The length of heart shaped gems is measured from a hypothetical line joining the tops of the lobes, rather than from the cleft.

[Correct measurement sites for common shapes: Graphic courtesy of www.tripps.com] Answers to the thought exercises for this lesson. (If you don't understand why these are the correct answers, then it's a good time to email me and ask!) 1): Troy ounce. If we use carats, then it's easy to decide on the Troy ounce which weighs 156 ct. compared to the English ounce's 142 ct. 2): English pound. Since there are only 12 Troy ounces in a Troy pound, then there are only 12 x 156 or 1872 carats in a Troy pound, whereas there are 16 x 142 = 2272 carats in an English pound, as English pounds have 16 ounces each.

You have now completed the web lecture for the second lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the non26

graded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Three: Physical Properties of Gems

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PHYSICAL PROPERITES OF GEMS Properties of Gemstones: There are two sets of characteristics possessed by every gemstone, and by which they are studied, identified and evaluated: 1) physical properties, and 2) optical properties. In this lesson we'll be concerned with physical properties: those which do not depend on the gem's interaction with light to be expressed or measured. (In the next lesson we'll look at the optical properties). All properties of gems (whether physical or optical) derive from the underlying three dimensional structure and chemical composition of the gem. Or to put it another way, the chemical elements that make up the gem, and how the atoms of those elements are put together to create its inner structure, determine all those properties that we can see, feel, and measure. Amorphous vs Crystalline: The most basic discrimination that can be made, based on internal structure, is that between gems which are amorphous, and those which are crystalline. Crystalline gems have a specific chemical formula, and a well defined, highly predictable internal structure, known as a crystal lattice. Amorphous gem species also have a specific chemical formula, but their constituent atoms are not arranged in such regular and predictable patterns as those of crystalline materials. Amorphous Gems "Amorphous" literally means "without form", but, of course, these materials have a form--> it's just not highly regular and predictable, nor is it expressed outwardly by the formation of crystals. Some examples of amorphous gems are: the natural glasses, amber, jet, opal, and "metamict" minerals. Natural Glasses: The atoms making up a glass (either natural or man-made) have been cooled from the molten state so quickly that they fail to assume a regular crystalline pattern. A volcanic glass, like obsidian, then, might be formed if a volcano released lava into the air or water such that it was very rapidly cooled--> this very same lava could, upon slower cooling, form a crystalline material (like basalt, for example).

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Obsidian ranges in color from light yellow through brown to black and can be transparent, translucent, or opaque. Those of our ancestors, who lived in areas of volcanic activity, made ready use of these natural glasses.

[Obsidian artifacts] In some cases, due to the presence of other minerals with different crystallization temperatures, when the molten material cools, crystal inclusions may be formed. These can give the obsidian an interesting pattern, or affect the structure in such as way as to cause an optical phenomenon, like iridescence. Although most obsidian is drab, single-color translucent material, two interesting and more showy forms of this volcanic glass can be seen below:

["Snowflake" obsidian, "velvet" obsidian] Tektites: Another group of natural glasses, known collectively as "tektites", are not found associated with volcanic eruptions, but rather in places which are believed to have been sites of meteoric impact. The heat and compression of the impacts are thought to have melted silica sand, and the molten bits which were flung into the air rapidly cooled into their glassy state.

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[Tektite from China] Although, like most obsidian, the various types of tektites are dull colors of green and brown, they are still much sought after by gem and mineral collectors. They have a following as well among those who ascribe mystical properties to these gems, perhaps because of their association with celestial events. The most commonly seen tektite is a green, near transparent type found in the Moldau River Valley in Eastern Europe, known as Moldavite. An intriguing light yellow form of natural glass has been found in several areas within the Libyan Desert, and, to date, has not been associated with a meteor impact, so its origin remains uncertain.

[Moldavite cabochon, faceted Moldavite in jewelry, Libyan desert glass] Amorphous Organics: A number of organic gem materials have an amorphous structure. Species like amber and jet which are composed of organic molecules, (those of evergreen tree resin, and the wood of certain hardwood trees, respectively) which have been altered into a near "plastic" polymeric state by geologic forces and time, are examples.

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[Reverse-carved amber cabochon, jet carving] Opal: Although opal is one of the most diverse gem species, with a large number of named varieties, all share a common structural feature. An electron-microscopic view of opal shows that it is made of row upon row of stacked silica spheres, the exact arrangement, pattern, and size of which determine the body color, transparency and degree of color play of the opal. Opal forms as a colloidial solution of tiny silica particles in water, and as the water is lost the material solidifies to a microscopically porous, amorphous state.

[Opals from Australia and Ethiopia] Metamict Minerals: Most zircon specimens that you will see, are crystalline gems, but a few pieces (generally a dull olive green color) have lost some, or all, of their crystalline structure, and have become disorganized internally to a glassy state. This transformation is due to the effects of radiation, and such a material is said to be "metamict". The radiation source is usually from impurities within the zircon itself, but can be from surrounding rocks. This phenomenon can occur naturally in several minerals, but zircon, and perhaps ekanite, are the only ones of gem significance. These glass-like zircons (sometimes called "low" zircons) do not have the same super-bright luster and brilliance of the crystalline type, and are mainly sought as curiosities by collectors. 31

[Metamict zircon] **Check the Text: If you look in the back of the Cally Hall book, you'll find a "Table of Properties" section that lists the structure of many gem materials. See if you can find a well known gem, not mentioned in this web lecture, that is amorphous. Crystalline Gems The highly regular, and sometimes startlingly angular shape of some well formed crystals can seem eerily out of place in the world of Nature, with its more familiar curving and flowing lines. It's no wonder, then, that a rich history of mystical and mythological lore pre-dates, and coexists with, today's chemical and physical understanding of crystal structure. Imagine the reaction of our ancestors, so used to the shapes and forms of flowing water, curling fire, gnarled tree branches, curving shell, roseate flowers and sinuous leaves, when they saw something that looks like the images below, perhaps in a mass of rock on a hillside, or upon cracking open an ordinary looking boulder:

[Natural pyrite cubic crystal in host rock, amethyst crystals inside a geode: Image courtesy of: Treasure Mountain Mining] The internal regularity that the outer features of such structures implies, was as evident to our ancestors as it is to us, but it was not until the beginnings of modern physics and chemistry (in the 17th - 18th centuries) 32

that some of the underlying causes came to be understood. Full revelation of the most intimate details of crystal formation and properties awaits future generations, but major gains were made in the early 1950's with the advent of a technique called Xray diffraction. Although definitely more"hi-tech", the principle behind this technique is essentially the same as used in an ordinary medical Xray machine. To illustrate: a beam of Xrays travels through your arm, let's say, to Xray sensitive film below. The dense tissue (bone) absorbs more of the Xrays than does the soft tissue, so the film is exposed differently, and a high contrast picture is made. In the case of mineral crystals, the dense areas (where atoms are closer together) absorb more Xrays than the less dense ones (where atoms are further apart), and a high contrast picture is produced. For those who have been trained in reading such photos, inner details of crystal structure can be deduced by interpreting the patterns. **Check the text: See page 37 of the Lyman text for such a photo. Single Crystal vs Aggregate Gems: Within the realm of crystalline gem materials, the major distinction to be made is that between those which are composed of macroscopically visible, single crystal units, and those which occur as a mass of interlocking or intermeshed microscopic or submicroscopic crystals. The pyrite and amethysts, pictured above, are examples of single crystal gems. If, however, you can imagine shrinking the amethyst quartz crystals down to very, very tiny proportions and pushing them together in random orientations such that you'd need ultra-strong magnification to resolve them, you'd have an idea of the internal organization of an aggregate gem, like chalcedony (an aggregate form of quartz). Both amethyst and chalcedony are the same species: namely quartz, so their crystals (whatever their size) are of the trigonal system, and their chemical formula is SiO2, but the difference in the crystal sizes and arrangement creates some notably different physical and optical properties in the two varieties. For example, amethyst, and other single crystal quartzes, are commonly transparent and one color, while chalcedonies, agates, and other aggregate quartzes are translucent to opaque and often have complex color patterns. Although single crystal and aggregate types of quartz are equally

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hard, the aggregates are notablytougher. Recall this pair of photos from Lesson 2 which also serve as good examples here:

[Single crystal (amethyst) and aggregate (agate) forms of quartz] Single Crystal Gems Single crystals can be large--> truck size or even bigger. I recall with pleasure an undergraduate college geology field trip made to Crystal Cave in Put-in-Bay, South Bass Island, Ohio. The cave, which was actually an enormous underground geode, had walls and a ceiling composed of huge celestite (or celestine) crystals. Check the web: This website has pictures from inside Crystal Cave:http://www.putinbayphotos.com/crystalcave/crystalcave.htm

[Celestite crystal cluster from Ohio,near Crystal Cave: Image courtesy of www.irocks.com] **Check the Hall text, pg. 105, if you'd like to learn more about celestite. Single crystal gems grow in clusters or individually, and they can be formed within, or attached to, another mineral, or loose, as so-called "floater" crystals. Single crystals can be quite small, but they will still qualify as single crystals (not aggregates), as long as they are large enough to be visible as 34

separate entities without high magnification. "Drusy" gems consist of such small, to tiny, single crystals, which have grown upon a matrix.

[Single Hanksite crystal]

[Quartz "floater"crystal cluster, spinel crystal in calcite marble matrix]

[Tiny single crystals of uvarovite garnet on a matrix (drusy) with inset showing them at 20x magnification] Aggregate Gems: Micro- vs Crypto-crystalline Microcrystalline aggregates: Aggregates with crystals that can be resolved with a light microscope are called microcrystalline. The standard way to view the crystals is with a very thin slice of the gem, and about 100 - 200x magnification. The most commonly known gem material that falls in this category is jade.

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[Microcrystalline aggregate gems: jadeite jade, nephrite jade] Cryptocrystalline aggregates: Aggregate quartz gems such as: agate, chalcedony, and jasper are generally referred to as cryptocrystalline (crypto, meaning "hidden"). This is because the minute crystals cannot be resolved with a standard light microscope, but are revealed only with an electron microscope, or by using specialized polarizing lighting, and very high magnifcation.

[Cryptocrystalline quartzes: agate, jasper, chalcedony] Gem Rocks For the sake of completeness, it should be mentioned that although the vast majority of amorphous and crystalline gemstones are composed of a single 36

mineral species (other than their minor inclusions), a few gem materials are classed as rocks. A rock is a variable mixture of two or more minerals. Perhaps the most familiar and valuable of the gem rocks is lapis lazuli, a mixture of the minerals lazurite, sodalite, Hauyne, calcite and pyrite. Other gem rocks include unakite (pink feldspar, green epidote, and quartz) and Chinese writing stone (white feldspar crystals in shist).

[Unakite, lapis lazuli, and Chinese writing stone, popular gem rocks] ********* Crystallograpy: It is beyond the scope of this introductory course (and beyond your instructor's ability) to delve deeply into the complex and rigorous field of scientific crystallography, however; it will be necessary for us to have a passing acquaintance with a few basics. This is because the majority of gems are crystalline, and the specific nature of their crystalline structure has bearing on both their outward form, and their physical and optical properties. The Crystal Systems Scientific analysis has determined that there are seven** basic plans upon which all mineral crystals are built--> they are known as the "crystal systems". Each of the systems has a unique architecture, based on the lengths, and angles of intersection, of planes through the crystal called "axes", about which there are degrees of symmetry. Huh?, I hear you say--> perhaps a diagram would be helpful at this point:

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[Crytstal systems figure courtesy of Dr. Brad Amos] (**You may find in some references, that six, rather than, seven systems, is the number given. The seeming discrepancy occurs because some sources consider hexagonal and trigonal to be different aspects of the same basic 38

plan, and lump them together, but for our purposes in this class, as described in our two texts, we'll use seven. ) Unit Cells The innermost structure of each crystal is based upon atomic-scale building blocks that exhibit the symmetries shown in the "axes" column in the diagram above. These tiny building blocks are called "unit cells". The shape of a unit cell is different in each of the crystal systems: a cube in the cubic system, a "brick" for the tetragonal system, etc. These tiny structures assemble themselves as the crystal grows, and build the crystal up to its finished size and shape. It might seem, from the diagram above, that there are only a few outward forms (or "habits") possible, given the seven types of unit cells available--> but in the real world, we find that mineral crystals come in nearly an infinite set of shapes and sizes. How can this be? Because it is easiest to visualize, I'll use the cubic (also known as isometric) system to illustrate. The unit cell in this system is a cube: picture a baby's building block set, or (if you live here in Nevada), dice. Is it possible to build a big cube out of little cubes?... Sure, just stack them up 5 x 5 x 5 or in any other equal dimenisons, and your many little cubes become one big one. Such is the mechanism by which the impressive pyrite cube seen earlier in the lesson was built from the little, cube shaped, unit cells of the mineral pyrite. It shouldn't surprise you, then, to learn that diamond (which is also a member of the cubic crystal system) is sometimes found in natural cubes.

[Natural diamond crystals, showing the "cube" crystal habit, natural cubic diamond crystals drilled as beads for earrings] But using those same blocks or dice, can you build a pyramid?... You bet! Start with a square base, and decrease each square layer uniformly until to get to the top single cube. (5 x 5, then 4 x 4, then 3 x 3, etc). Look at the 39

second of the "typical forms" for the cubic system shown in the diagram above. Can you see it as two pyramids attached to each other, base to base? That shape is called an octahedron (meaning eight sides) and it's a common form seen in the crystals of gems of the cubic system. (Why are the faces of the octahedra so smooth?--> because the cubic unit cells are really, really tiny, and there are enormous numbers of them!

[Fluorite and spinel octahedra--To which crystal system do fluorite and spinel belong?] Crystal "Habits" Characteristic crystal forms such as those above, that are easily recognized, and are typical of a particular mineral, are known as its crystal "habits", but no gem species is limited to these ideal shapes. You can also see, I'm sure, that it's quite possible to build a random looking structure out of your blocks or dice, one that has no readily categorizable outer shape. This frequently seen habit in crystalline gems is referred to simply as "massive". Now, recognizing that each of the seven crystal systems has a different unit cell, and that these unit cells can be put together in many, many ways, is there any wonder that the diversity of crystal forms in Nature is staggering, and such a challenge, and delight to mineral specimen collectors? A few of the crystal habits, due to their similarity to common objects, are especially recognizable and have acquired special names, as demonstrated by the specimens below:

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[Acicular (needle-like): golden rutile crystals in quartz, "puffball-like"mesolite specimen of radiating acicular needles (image courtesy of Treasure Mountain Mining)

[ Prismatic (pencil-like) tourmaline crystals, red beryl crystal in matrix: Image courtesy of www.irocks.com]

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[Dendritic (like tree branches): quartz with black manganese dioxide crystal inclusions, sandstone matrix with iron oxide dendritic crystals on surface, dendritic native copper crytals]

[Drusy (like sugar or powdery snow on a surface): rainbow pyrite crystals on matrix, botryoidal (seen in aggregate gems only, like a bunch of grapes or bubbles): blue chalcedony] Check the web: This site has an extensive list of these, and many other habits, and a spectacular picture of an unusual pyrite crystal habit: http://www.answers.com/topic/crystal-habit Crystal Growth Factors affecting crystal appearance: Although the crystal system and unit cell which are characterisitic of a particular gem species set certain parameters in regards to their formation, there are also a mulitude of environmental factors that will determine precisely what size, shape, color, and clarity a particular crystal will have. (We'll be taking a look at how different species of gems are formed in Lesson 10, "Gem Formation", but regardless of the specifics, all gem formation processes are affected by the same factors listed below). •

Temperature/Pressure: the effect of rapid versus slow cooling of a melted material has already been alluded to, but there is more to the story. The same molten mass of atoms, or the same solution, or vapor of materials can crystallize differently, depending on the temperature and pressure at the time, and in the place, where crystallization occurs. This is because there can be more than one stable crystal lattice composed of the same atoms. The various stable configurations that a particular gem species can crystallize in, are referred to as its "polymorphs". 42

Polymorphs When two materials have the same chemical formula but have crystallized differently (due to each being subjected to different temperature/pressure conditions at formation), they are called polymorphs. The most famous examples are diamond and graphite. Both have the same chemical formula (just C, pure carbon), but the "lead" in your pencil and the diamond on your finger, obviously exhibit quite different properties. Graphite crystals are formed of sheets of tightly bonded carbons atoms in layers which are very loosely bound to each other, allowing lots of slipping and sliding. Diamond crystals have each carbon atom bonded tightly to four others surrounding it in all directions, so the whole structure is very strong and durable.

[Graphite and diamond (uncut dodecahedral (12 sided) crystal), polymorphs of carbon] Another interesting gem example is the case of Al2SiO5 which can crystallize in the orthorhombic system as Andalusite, or in the triclinic system as kyanite.

[Polymorphs of Al2SiO5 : Andalusite, kyanite] Check the web: For those of you with an interest in pharmacology or medicine, a recent article by Alexandra Goho in Science News reviews some of the "polymorphic" difficulties drug companies run into as they attempt to produce crystalline drugs. The environmental conditions that lead to the production of ineffective or even toxic polymorphic forms of drugs are difficult to identify and control.http://www.sciencenews.org/articles/20040821/bob9.asp 43

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Space available: crystals often form in cavities, cracks, bubbles, and other cramped places, the size and shape of which will limit growth possibilities. Some directions of potential growth might be unavailable or limited, while others afford plenty of "growing room". It can also occur that two or more crystals which start growing in a space independently, can contact and/or interpenetrate each other resulting in "twinning". Chemical elements present: Each species requires a particular set and proportion of chemical elements for its basic makeup, and cannot grow without them. Nonrequired elements, though, which incorporate into the growing crystal in trace amounts can have dramatic effects on the appearance (usually color) of the gem. For example, a very small amount of the element chromium, when present along with the necessary aluminum and oxygen, turns, what would otherwise have been colorless corundum, into red ruby. In addition, fluctuations in the amount or type of growth materials present can lead to color zoning, as well as to the creation of crystal "phantoms" and "negative" crystals. Other minerals present: Minerals do not usually form crystals in complete isolation. As a particular crystal is forming, other minerals, also in the process of crystallization, can be captured by it (to show up as inclusions) or capture it. Exactly how this plays out will depend on the relative crystallization temperatures and pressures required by the materials in the group.

[Quartz from Madagascar with fluorite crystal inclusions, inset picture at 10x] Special Growth Phenomena: Twinning When growing crystals of the same mineral share one or more faces, the result is a crystal "twin". Depending on the nature of the twinning, which 44

can be on either a visible, or a microscopic scale, the shape of the crystal might be dramatically affected, or the material's properties could be noticeably altered. Sometimes, evidence of twinning can be seen in a crystal or cut gem due to unusual color or inclusion patterns.

[Twinned quartz crystals in "rabbit ear" form: (Image courtesy of Treasure Mountain Mining), twinned octahedral diamond crystals which form a characteristic flattened triangular "maacle", rare "hour glass" twinned gypsum cyrstal from Australia: Image courtesy of www.irocks.com]

[Evidence of twinning in quartzes: in the pattern of lepidocrosite platelets of the cabochon, and in the alternating color sectors of the crystal slice.] Phantoms and Negative Crystals: Due to changes in environmental conditions, starts and stops of crystal growth occur. When other minerals, which are favored in the new conditions, start to grow, they sometimes crystallize on the "old" faces of the temporarily inert material. When conditions change, and the host once again starts its growth, evidence of the pauses may now be visibly captured as outlines of the temporary stopping points, called "phantoms".

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Likewise, certain conditions may completely block the growth of an interior portion of a crystal leaving a void which is bounded by the sides of the crystal around it--> at first glance this "negative" crystal looks like a solid crystal inclusion, but it is indeed empty.

[Edenite phantoms in quartz, hematite phantoms in calcite, a negative crystal in quartz] Pseudomorphs: The term "pseudomorph" literally means false form. A pseudomorph is, in a way, the opposite of a polymorph. Whereas polymorphs are different crystal forms of the same chemical compound, a pseudomorph shows a crystal form which is not one recognized for its species. To put it another way, it's the case of one mineral taking on the outward form of another while keeping its chemistry unchanged. Let's take the example of Goethite which is an iron oxide mineral that crystallizes in the orthorhombic system. A glance back at the diagram for the crystal systems shows us that orthorhombic gems do not form in perfect cubes. Pyrite, however is an iron sulfide mineral (in the cubic system) that frequently forms crystals shaped like perfect cubes.

[Pseudomorphs: Goethite ps. after pyrite: Image courtesy of www.irocks.com, copper ps. after aragonite] In the first picture above you see what appears to be a twinned pyrite crystal, but chemically and physically it tests not as pyrite, but as Goethite, the second picture shows what appears to be a hexagonal crystal, but it is made entirely of the cubic system mineral, copper. Pseudomorphs occur when environmental conditions occur that cause the replacement of one 46

chemical compound with another withoutaltering the pre-existing three dimensional structure. Mineralogically, the item is named as an "X" pseudomorph (ps.) after "Y". (Goethite pseudomorph after pyrite, for example. ) Likewise those "petrified" fossils spoken of in Lesson 1 are more technically known as "chalcedony pseudomorphs after bone", or "opal pseudomorphs after wood". Check the web: this website has examples of the several different processes involved in the formation of pseudomorphs and some neat pseudomorph pictures:http://www.gc.maricopa.edu/earthsci/imagearchive/pseudomorphs. htm Chemical Groups of Gems: In addition to categorizing gems by their three dimensional structures, we can also view them as belonging to various chemical groups. Due to their related chemistries, some quite different looking gems share some of their basic properties, while other gems which look rather similar, differ markedly, due to their unlike chemistries. Even if you haven't yet taken a college chemistry course, you are undoubtedly familiar with the basic idea that the material world around us is made of up of units (atoms) of unique substances called elements. Examples of elements would be carbon and aluminum. These elements are held together in crystal lattices, molecules and amorphous materials, by attractive forces called chemical bonds. In the world of minerals, certain groupings occur quite commonly. For example, oxygen frequently occurs bonded to atoms of a metal (like iron or aluminum). We call such compounds oxides, and oxide gems have some characteristics in common. There are dozens of chemical groups which could be listed if all gem species were taken into account, but in this course, you will be required to recognize, and recall, only five major groups, the: silicates, oxides, carbonates, phosphates and native elements. Accounting for nearly 60% of gem species, silicates are the most important group, closely followed in prominence by the oxides. These two groups have in common, that their member species tend to be relatively hard and stable, while the carbonates and phosphates are generally softer, and susceptible to attack by acids. Recognizing which chemical group a species belongs to is simple, as long as you know what to look for.

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Silicates: Regardless of what other atoms are present (usually one or more metals), gems of this category will have in their chemical formulas some number of Si and O (silicon and oxygen) atoms listed together as a group . For example, as in the polymorphic species from above: Al2SiO5--> here we see the group of one silicon atom and five oxygen atoms, which identify the polymorphs Andalusite/kyanite as silicate gems. The numbers of Si and O will vary, depending on the species, but will always appear as a unified group. In general they tend to be hard, transparent to translucent, and of medium density. In this very large class are all the beryls (aquamarine, emerald, etc.), all the quartzes (amethyst, rose quartz, agate, etc.), all the feldspars (sunstone, moonstone, etc.), all the garnets (pyrope, Spessartite, demantoid, etc.) topaz, tourmaline, zircon, and many other lesser known species. **Check the text--turn to the back pages of the Hall text and look up each of these to practice recognizing the characteristic silicate chemical groupings. Do this for all the other gems shown in the four other groups below! Here's the first one for you: looking up emerald on page 152 you see : Be3Al2(SiO3)6 ......

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[Emerald, amethyst, tiger'seye quartz]

[Moonstone, rhodolite garnet, blue topaz]

[Bi-colored tourmaline, white zircon] •

Oxides: This group will have one or more oxygen atoms (not grouped with silicon, phosphorus or carbon) in their formulas. Many oxides are important ores of metals or valuable gemstones and tend to be quite hard and rather dense. Amongst the members of this group are corundum Al2O3 (ruby and sapphire), spinel, hematite and chrysoberyl.

[Ruby, spinel]

[Hematite, chrysoberyl] 49

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Carbonates: The grouping CO3 identifies the carbonate gems such as rhodocrosite, malachite, calcite (CaCO3), and azurite. They are generally soft and often brightly colored. They dissolve readily in hydrochloric acid.

[Rhodocrosite, malachite]

[Calcite, azurite] •

Phosphates: A PO4 group is the identifying chemical landmark for gems of this class. Many of these gems have very complex formulas, but do not be intimidated, you can still see the phosphate group in there! A highly variable group, in general they are soft, fragile, and brightly colored. Turquoise, and apatite are notable phosphate gems.

[Turquoise, apatite] •

Native Elements: This is the easiest group of all to recognize, as it consists of one and only one element. All the precious jewelry 50

metals such as gold, silver and platinum belong to this group, as does diamond.

[Native gold from Nevada, gold in quartz necklace, platinum nugget: Image courtesy of www.irocks.com]

[Diamonds: image courtesy of www.thaigem.com] Two interesting native element examples, not used as gems, but often sought by collectors are sulfur and mercury. Pure sulfur occurs in bright yellow crystals which would tempt the faceter if they were not so heat sensitive that just holding them in the hand causes them to crack, and rare native mercury has the distinction of being the only metal found in a liquid form at normal ambient temperatures.

[Crystals of pure sulfur from Mexico: beautiful to look at but too fragile to touch, droplets of liquid native mercury in matrix rock from California: Images courtesy of www.irocks.com] 51

Major Physical Properties Although there are a dozen or more physical properties which can be measured, in this course we will concentrate on just a few. In particular, our focus will be on those which are either visible directly, or measurable with minimal equipment, and those which are most important as indicators of a gem's identity, and/or its suitability for particular uses: Cleavage: In the three dimensional structure of certain crystals, atoms are bound more tightly to each other in some directions and more loosely in others. As a consequence, when strong forces are applied, relatively clean breaks may occur in these "weakest link" directions. These breaks, which can sometimes be so smooth as to appear to have been polished, are called cleavages. The number of directions in which a particular material cleaves, the ease with which that happens, and the "perfection" of the breaks are used to quantify this characteristic. Since cleavage, or lack of it, is a species trait, it also serves as a good gem identification criterion. In the examples below, the number and completeness of cleavage of three species are shown. Species with easy or perfect cleavage, particularly when such is the case in multiple directions, are poor risks for most jewelry applications.Not all gems show cleavage however, for example tourmalines, sapphires, and garnets do not.

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[Apatite: two, imperfect (note that cleaved surfaces are somewhat rounded and irregular); spodumene: two, perfect (note extremely flat, smooth breaks), fluorite: four, perfect] Food for thought: Far from being a matter limited to academic interest, knowledge of gem cleavage has practical value, both as a means of gem identification, and in the appropriate fashioning and selection of gems for a particular use. (Answers to the questions below are found at the end of the lesson). Question 1: Suppose you're a budding gem cutter or collector, and you happen to be at a swapmeet where a vendor has some transparent pink gem rough to sell. He knows that it is either Kunzite (pink spodumene) or pink tourmaline, but just can't remember which one. You have been wanting some pink tourmaline, so you look at the material closely and can't find any evidence of cleavages, even using your 10 power magnifier. Of the two choices, which is it most likely to be? Question 2: A big decision is coming up in your life--> you are about to choose an engagement ring. Not being a slave to tradition, you are considering a colored stone for the piece, rather than a diamond. You want a blue stone, and your top contenders are: blue topaz, and blue sapphire. Considering that engagement rings are worn all day, every day, for many years, you do not want a stone that is likely suffer a cleaveage that will crack or break it. Which is your best choice? (Hint: look up topaz in the Lyman text pg. 128). 53

Question 3: You've found a beautiful piece of apatite rough and want to have a stone cut from it . You approach your friend who is a facetor, and ask him/her to cut you a marquis shaped stone from the piece. The cutter declines and says they will cut an oval or round but not a marquis. Why? Miners have long used the cleavage properties of gems in trimming the stones they find. "Cobbing" is the act of smacking a piece of rough sharply and precisely with a hammer to break off any unstable (already partially cleaved), or included areas. Knowledge of the cleavage planes in the material being mined is essential to efficient use of this technique. The use of cleavage is perhaps most well known in diamond cutting. We've all seen photos or videos of that tense moment when the diamond cutter inserts the wedge at a particular spot on the diamond and strikes it with a mallet. If all goes well, the stone splits precisely where the cutter wanted, and expected, it to. It is said that the expert that first cleaved the (up to that time) largest rough diamond ever found (The Cullinan) had studied it for months to determine its cleavage planes, and upon striking the first blow fainted dead away from anxiety. All was well, however. **Check the text: See page 7 in the Hall text to view the largest of the many cut stones from the Cullinan, in its home in the Royal Scepter of the British Crown Jewels). Fracture: Whereas cleavages occur only in some gems, and within those, only in certain directions, fractures can, and do, occur in all gems, and in any direction. A fracture is a break which is not along a cleavage plane. With sufficient force, any gem will fracture, although some do so more readily than others. The edges of fractures are not smooth like those of cleavages, but they do tend to have one of several basic appearances. Playing on the resemblances of certain fracture types to well known surfaces and objects, terms like conchoidal (shell-like), splintery, uneven, step-like, and granular are used. Like cleavage, this is a species specific characteristic which has value in the identification of gems.

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[Citrine quartz: conchoidal, Charoite: splintery]

[Turquoise: granular, coral: uneven] Conchoidal fracture is the most common, and is found in corundum, beryls, all the quartzes, opals, and both natural and man-made glasses. Turquoise and coral are commonly simulated by glass.... So: Question 4: You are offered a bag of cut turquoise or coral at a gem show. The color is lovely and the price is very tempting. You notice that one of the pieces in the parcel has a broken edge which you examine with your 10x magnifier. With no knowledge other than what you've learned about fracture, what might you see on that broken edge that would tell you that this was not real turquoise or coral after all? Durability Factors In Lesson One, the concept of gem durability was introduced and described as being made up of hardness, toughness and stability. Let's now look at each of these factors in more detail. Hardness: The tendency to resist scratching in a gem is known as its hardness. Of the three factors comprising durability, it is the most familiar. Even those folks with just a passing interest in gems know that they can be ranked on a scale of hardness. Hardness is primarily the result of the strength of the chemical bonds between the gem's constituent atoms (how tightly they are bound to one another). 55

The hardness of a gem affects its wearability, luster, and resistance to cutting and polishing. All other factors being equal, harder gems are more useable in jewelry, develop a brighter surface luster, and take more time and effort to cut and polish. They will retain their polish longer than softer gems, given equal wear and tear. The familiar 1-10 Mohs' Scale of hardness, is not an absolute measure, but rather a relative one ---> a kind of "pecking order". Gems ranked at a higher number on the scale can scratch those ranked lower, and will in turn, be scratched by those whose number is higher than theirs. Frederich Mohs, a 19th century German mineralogist was the originator, and we still use his scale, with the minerals which he designated as reference points today. For example, (softest) talc = 1, quartz = 7 and diamond = 10 (hardest).

[Talc, the softest on the Mohs' scale, diamond, the hardest] **Check the text: (Pg. 16 in the Hall text shows a picture of all of the "type" minerals for the steps on the scale) In mineralogy, one of the key tests commonly used for purposes of identification is a "scratch" test, which is done with a set of implements known as hardness points. These, usually steel, "pencils" are tipped with various minerals (or metals) of known hardness. By drawing them across the surface of an unknown mineral sequentially, the tester can determine the sample's approximate hardness. In gemology, such tests are rarely used as they are destructive in nature. Exceptions might be in testing the bottom of a carving, or a piece of gem rough, or a bit of material which has broken off. Another drawback of the standard hardness points is that they are not precise, but limited to giving a "ballpark" estimate. In a laboratory setting, exquisitely precise measurements can be made with sclerometers. These devices use diamond-tipped, hydraulically operated 56

probes, and can give an absolute reading on the force necessary to penetrate the surface of a material. Check the text: (Pg. 16 of Hall's book, you can see in the "Knoop"Scale: the results of such sclerometer tests using the Mohs' indicator minerals. A quick study of the diagram makes it clear that the Mohs' scale is not linear. Note that a mineral with a reading of 5 on the Mohs', is not penetrated by half the force needed for a material ranked at 10. Corundum at 9 on the Mohs' is often incorrectly spoken of as "almost" as hard as diamond (10). In reality it takes many times as much force to penetrate a diamond surface as a corundum one! Not many hikers, nature lovers, or rockhounds carry hardness points with around with them on their treks, but the use of just a few ordinary materials can allow such individuals to do pretty good hardness tests in the field. The Practical or Field Mohs' Scale 1-2: easily scratched by fingernail 3-4: scratched by copper coin 5-6: easily, and not so easily, scratched with pocket knife 7: scratches window glass/scratched by steel file 8-10: scratches window glass, but not scratched by steel file: Hardness can be directional. This is actually quite understandable, as it depends on chemical bonds which can differ in strength, and in distance from each other, depending on which axis of the crystal we are observing. Generally such differences are relatively small and of litttle consequence, but there are two notable cases where they are dramatic and important. 1) Kyanite is notoriously difficult to cut because of its extreme directional hardness differences. 2) Diamond cutting would scarcely be possible unless the cutters could use the directional hardness of that gem to their advantage (More about diamond cutting to come in Lesson 7). Check the text: Page 133 in the Hall book gives more information on kyanite's directional hardness properties. SOFT GEMS:

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[Ivory and jet: 2.5, pearl: 3, sphalerite: 3.5, fluorite: 4] GEMS OF INTERMEDIATE HARDNESS

[Scapolite: 6, Tanzanite: 6.5; garnet: 7 - 7.5 depending on species, tourmaline: 7.5] HARD GEMS

[Spinel & topaz: 8; chrysoberyl: 8.5, sapphire: 9] Toughness: The tendency to resist breaking and chipping is known as a gem's toughness. This property is controlled primarily by two factors: the readiness of a material to cleave in single crystal gems, and the presence or absense of certain structural characteristics in aggregate and/or amorphous gems which promote strength and cohesion. 58

All other factors being equal, the harder the gem, the tougher it will be, but all other factors are not always equal. Take the case of topaz, for example. At hardness 8 it seems to be a pretty rugged gem, but if we consider its strong tendency to cleave in one direction, in reality, it is rather fragile. Likewise, diamond, the "star" of the hardness game, is only ranked as "good" when it comes to toughness because of its cleavage and fracture potential. Diamonds are usually cut with a flat culet facet at the tip of their pavilion, rather than coming to a sharp point as do colored stones. This is due to the likelihood of a fracture (or cleavage) in the fragile culet zone. When purchasing a diamond it is a good idea to check the girdle under magnification to make sure that it is not excessively thin, as this is another site of special vulnerability. Likewise, the corners and points of cuts like baguettes, trillions and marquis are vulnerable, and should be protected by the mounting when used in jewelry.

[Fracture on the girdle of a diamond: Image courtesy of Martin Fuller, cleavages on diamond with classic "staircase" pattern] On the other hand, nephrite jade with its hardness of 6.5 might seem to be delicate, but due to the felted, fibrous nature of its aggregate crystals, it is literally the toughest gem on Earth! So it is with pearls, which with their extremely low hardness, would barely be wearable at all, except for their moderately good toughness. It results from the layered, overlapping nature of the aragonite mineral plates of which the pearls are made, and the proteinaceous "mortar" that holds these brick-like layers together. Check the Web: In this short article with interesting micro-photos, researchers summarize recent advances in materials science whereby they attempt to make an artificial material with the structure and toughness of Mother of Pearl (nacre) that might be used, among other things, for bone grafts. http://www.sciencenews.org/articles/20060128/fob2.asp

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Toughness affects both wearability and resistance to polishing. Jade gems thousands of years old are as beautiful today as when they were first made. A well polished jade is a sign of a dedicated and skillful lapidary, as its structural characteristics make it susceptible to "undercutting" and an "orange peel" surface effect if not handled expertly and with patience. There is no numeric scale on which toughness is measured, rather, relative terms such as: exceptional, excellent, good, fair and poor are used. FRAGILE GEMS

[Topaz, sunstone, sodalite, serpentine: all poor] GEMS OF INTERMEDIATE TOUGHNESS

[Tourmaline, iolite: fair; chrysoprase (quartz), diamond: good] TOUGH GEMS

[Sapphire, hematite: excellent; jadeite jade, nephrite jade: exceptional]

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Stability: Stability in a gem is a measure of its ability to resist changes due to exposure to light, heat and/or chemicals. Not only does stability affect wearability, but it also dictates appropriate ways of fashioning, cleaning and storing the gems. Most gems are stable, but a few (even some quite popular ones) are unstable, and must be handled accordingly. The Effects of Heat Dehydration: Heat is a factor that can create problems with certain gems. In some cases, the mineral comprising the gem is "hydrated", that is, it contains water molecules which adhere chemically with varying degrees of tenacity. When the water is rather loosely attached, hot dry air can lead to loss of some of the water, and changes in the color, or transparency of the gem. Even more seriously, its loss can cause a network of cracks to form in the gem, in a process called "crazing". Opal is the most well known gem for which this is an issue.

[Badly crazed opal: Image courtesy of Bill Wise] It is sometimes suggested that opal gems and jewelry items be stored in water or oil when not being worn --> this is NOT good advice. Water will not hurt the opal, but it will not help it either. The type of "chemically linked" water that is lost when crazing occurs cannot be replaced by soaking, nor can this procedure be used as a preventative. It is the structural details of the particular type of opal, including the percentage of water in it, that determine the likelihood of crazing. Reputable opal dealers "proof" their material before it is sold, by subjecting it to hot dry conditions for months. Generally, those pieces that survive such treatment will be stable under normal wearing conditions. (Leaving an opal on a car dashboard for hours in the August sun, or forgetting that your opal ring is in your pants pocket, and then putting the pants in the dryer for an hour on high, would NOT be examples of normal wearing conditions! Soaking in oil is an especially bad idea as opal is a porous gem and the oil seeps inside and then discolors over time, degrading the gem's beauty. ) 61

Thermal Expansion: Another problem that heat creates for some gems is caused by their inherent capacity for "thermal expansion". This is a yet another physical characteristic by which gems differ. Diamond is notably stable to temperature changes (with slow and even rates of thermal expansion), so much so, that jewelers can pour molten metal into molds containing wax models with the diamonds already in place, to cast pre-set jewelry pieces. Other gems, such as apatite, expand so rapidly with sharp rise in temperature, that their crystal structure is damaged, and they crack or even shatter. Heat sensitivity of that degree makes it very important for lapidaries cutting such gems, and jewelers working on mountings containing them, to keep the gem cool during these processes. The Effect of Inclusions: Although a gem might be quite temperature stable itself, inclusions of other minerals within it, could have different degrees of thermal expansion from their host. This situation becomes quite important in the heat treatment processes used to enhance gems. Internal inclusions can literally explode or, less dramatically, expand, and in doing so, create internal "stress cracks" in the gem being treated. (For this reason, it is standard practice among Tanzanite heat treaters to heat only cut stones which have had virtually all the inclusions removed, and to avoid heating rough material.) To an extent, heat treaters can ameliorate such effects by very, very, slowly raising and lowering temperatures. Tanzanite heaters might take 12 to 24 hours to incrementally reach the desired temperature, hold the gems there for several hours, and then take another 12 to 24 hours to gradually cool them down. At the highest temperature levels, though, such as those required to heat treat corundum, or those used for "color diffusion" processes, nothing can prevent heat damage. This is good news in a sense, though, because such internal and external cues to the heating, help the jeweler or gemologist spot the gem as one which has been subjected to extreme temperatures.

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[In the center of this picture of the interior of a gem under high magnification, you see an included, heat shattered crystal, broken into four pieces, and a series of stress fractures surrounding it--> positive evidence of high heat treatment in this gem] There are cases where thermal expansion characteristics of gems are used to deliberately induce cracks or stress fractures. Pieces of amber which have been heated, and then quickly cooled, develop disk-like stress fractures called "sun spangles" which some consider to be attractive.

["Sun Spangles", stress fractures in heated amber] A very old method of dyeing gems, which is still occasionally used today, is called "quench crackling"--> single crystal gems, like quartz, for example, which would ordinarily not absorb dye are heated and plunged in cold water to fill them with cracks that, then, can take up the dye, giving apparent color to the whole piece.

[Quench-crackled quartz pebble dyed pink, the closeup shows clearly that the pink dye is confined just to the cracks] 63

Other Environmental Factors: Light: Some gems can fade or change color when exposed to light. An extreme example of this phenomenon is seen in the rare mineral pyrargyrite which must be kept constantly under opaque covers or else light exposure quickly renders its originally red color completely black. In the case of gem minerals, there are only a few to be concerned about. Kunzite (pink spodumene) can lighten in color with long term exposure to bright light, and is sometimes suggested as an "evening only" gem. Certain brown topazes, notably those from Mexico, can lighten dramatically, even becoming colorless with continuous light exposure. Chemicals: Exposure to various chemicals can ruin the polish of, and/or discolor certain gems. Two important cases would be carbonate gems, like rhodocrosite, which degrade due to a chemical reaction when exposed to acids, and amber which can be dissolved by acetone. It is doubtful that a drop of lemonade, or vinagrette salad dressing, or a bit of spilled nail polish remover would harm such stones, but acid vapors found in the polluted air of many cities can take their toll over time, as can some intense solvents, such as paint strippers, which might be used in the home or workplace. A dip in certain jewelers' solutions, like the hot "pickle" used to remove oxidation from metals, would be devastating to rhodocrosite, while a few hours spent soaking in "AttackTM" (a solvent used to remove glues used in jewelry making) would ruin an amber gem. Most gems in the unstable category, however; are sensitive more in virtue of their porosity, than because of their chemical makeup. Pearls and turquoise are two gems well known for their propensity to absorb cosmetics, perfumes, body oils, sweat, etc., and to dull and discolor as a result. Often fine turquoise gems are given a final polish with a layer of colorless paraffin wax to help seal and protect them from such degradation. Lightly wiping chemically sensitive gems with a damp cloth after each wearing will help to keep them in good shape. Any gem which is suspected, or known, to be chemical or heat sensitive should be protected from steam or solvent cleaning methods. Such considerations also become a factor in gemological testing in that, turquoise, for example, cannot be placed in the chemicals that would be used to determine specific gravity, or those used in relative refractive index testing. UNSTABLE GEMS 64

[Apatite and opal: heat sensitive, Mexican brown topaz: fades in light, turquoise: porous and likely to discolor with exposure to various materials]

Specific Gravity Specific gravity, also known as relative density, differs widely among gemstones, and is one of their most important physical characteristics from the viewpoint of gem identification. Specific gravity (SG) is the ratio of the weight of one unit volume of the gem to the weight of the same unit of water. For example, to say sapphire (corundum) has SG = 4.0, means precisely that a cubic inch of sapphire weighs four times as much as a cubic inch of water. In natural gems, SG values range from just over 1 (1.08 for amber) to just short of 7 (6.95 for cassiterite). LIGHT GEMS: SG < 3.O

[Amber: 1.08;, shell: 1.30, meerschaum: 1.50, opal: 2.10] MEDIUM DENSITY GEMS: SG: 3 - 4

[Andalusite: 3.16, jadeite: 3.33, chrysoberyl: 3.71, sapphire: 4.00] HEAVY GEMS: SG > 4

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[Zircon: 4.69, scheelite: 6.10, anglesite: 6.35, cassiterite: 6.95] A curious student might ask at this point: "Why do specific gravities differ so much?" The answer, satisfyingly, goes back to the basic premise of this lesson (that all physical properties of gems are the result of their chemical and structural makeup). The various elements of which gems are made have atoms of different weights. Atoms of gaseous elements like hydrogen and oxygen are light, while metallic elements like aluminum and iron have heavy atoms. Chemists use "atomic weights" to describe elements --> rounding them off, here are some examples: hydrogen = 1, carbon = 12, oxygen = 16, aluminum = 27, silicon = 28, calcium = 40, iron = 56, zinc = 65, and lead = 207. It's quite logical, then, that a cubic inch block of lead is going to weigh much more than a cubic inch block of aluminum. Extending that idea to gems, we can see that if a gem is made of relatively heavy elements it will have a greater SG than if it is made of lighter ones. There is a second factor to consider, however; which is the structure: How are those atoms put together? Are they tightly packed or loosely arrayed? The examples below will help to illustrate the interplay of chemical make-up and crystal structure in determining specific gravity. 1) First, let's look at the case where structure is held constant but atomic makeup is different. Here, we'll compare two minerals that have the same crystal structure, in this case they both are of the orthorhombic system, and, they have identical chemical formulas except for substitution of one element for another. Calcite: CaCO3 -vs- Smithsonite: ZnCO3 Both consist of five atoms per unit: either a Ca or a Zn plus one carbon and three oxygens. Both are put together with the "atomic packing" characteristic of the orthorhombic system of crystals. Their SGs differ though, with calcite = 2.71 and Smithsonite = 4.35. 66

Looking at the list above and seeing that calcium's atomic weight is 40 and that of zinc is 65 gives us our answer! Question 5: Suppose we had a 6 mm round calcite, and a 6 mm round Smithsonite, cut to the same proportions--> Which would be heavier? Or to turn it around, if we had a one carat round calcite and a one carat round Smithsonite, which would be bigger? 2) Now to examine the effect of structure, by holding the chemical makeup constant... Remembering the concept of "polymorphs" from the first part of this lesson, we'll compare calcite and aragonite. Both have the same chemical formula, CaCO3: Calcite: orthorhombic crystal system -vs- aragonite: trigonal crystal system Both are made up of the same elements in the same proportions, but those building blocks are put together differently so their SGs differ, with calcite = 2.71 and aragonite = 2.94 Question 6: Suppose we had a 6 mm round calcite, and a 6 mm round aragonite, cut to the same proportions--> Which would be heavier? Or to turn it around, if we had a one carat round calcite and a one round carat aragonite: which would be bigger? Question 7: Look up the SGs for gold and platinum in the back of the Hall text. (Even if platinum sold for the same price as gold, which it doesn't) why would it cost more to make a particular size and type of ring in platinum than in gold? Measuring Specific Gravity: Although SG measurements can be made on either rough or cut gems, the gems must be unmounted, and composed of a single material. You cannotdo a SG measurement on a gem that is set in a piece of jewelry, or on an assembled stone, like a doublet. Porous gems cannot be measured with at least two of the techniques, as the liquid they absorb affects the SG measurement, and, in some cases, can harm the stone. Detailed reference books meant for mineralogists or gemologists will list SGs for gems as a range, rather than a single number, due to the fact that individual specimens will differ slightly based on the number and type of their inclusions. (Your texts, meant for non-professional use, however, use a single number average of the SG range for the gem species). There are several ways in which SG is

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measured, and they differ in precision as well as suitability to different gems and circumstances. Hefting: The crudest technique, but one that can be rather useful in some situations, is simple hefting. By lifting the gem and gently throwing it up in the air and catching it, a general feel for its density can be gained. This technique is often all that is needed to discriminate plastic and some glass imitations from the much denser gems they mimic. Conversely, jewelers who are intimately familiar with the heft of a 6.5 mm diamond (which will weigh almost exactly one carat) may be able to quickly pick out a 6.5 mm imposter because so many diamond simulants have SGs substantially higher or lower than diamond. Heavy Liquids: For most of us, though, in most circumstances, hefting would not supply enough information. One popular method is based on the principle of bouyancy: "an object will sink in a fluid of lesser SG, remain suspended in one of equal SG, and float in one of higher SG." This technique uses a set of "heavy" liquids with known SGs. By immersing the unknown gem material in the liquids, and observing its behavior, its approximate SG can be deduced.

[Heavy Liquids Testing Set, SGs of liquids are printed on bottles, dropper bottles are for calibration] To give a simple example, consider an unknown gem that floats quickly in the 3.05 bottle, sinks rapidly in th 2.57 bottle, and floats and sinks very slowly in the 2.67 and 2.62 bottles, respectively. That would tell you that the SG was between 2.67 and 2.62 and would allow you to rule out a great many minerals and focus any further tests on a smaller group of "possibles". Corundum (SG = 4.0) would behave quite differently from these observations, and could be excluded, while quartz, whose SG is 2.65 would behave precisely as described, and could not, therefore, be excluded. 68

Hydrostatic Weighing: By far the most precise technique for SG determination involves use of a specially modified weighing balance that allows a gem sample to be weighed in air (Wa), and also weighed in water (Ww). Using Archimedes Principle: "a body immersed in water weighs less by the volume of water displaced", and a simple calculation, SG can be determined with substantial accuracy. SG calculation: Weight of gem in air divided by the difference between the weight in air and the weight in water, or: SG = Wa/ Wa-Ww

[Hydrostatic weighing set-up consisting of an electronic balance with a special hanging basket apparatus in which the gem can be suspended in water without putting weight on the scale.] Again, an example. We have an unknown gem whose weight in air is 5.10 ct and whose weight in water = 3.20 ct. The difference in the air and water weights is 1.90 ct. Using the formula: SG = 5.10 ct/1.90 ct = 2.68. Looking in the tables at the back of the Hall book we quickly find several gem possibilities 69

close to that SG: quartz (2.65), coral (2.68), aquamarine (2.69), and scapolite (2.70). More importantly, than what it might be, a SG of 2.65 rules out a large number of possibilities that it cannot be. The gemologist, like other scientists, progresses most often by weeding out wrong hypotheses (as opposed to proving right ones!). Final Exam (just kidding!) Scenario: We have obtained an unknown transparent green gem from a jeweler, the label has fallen off the box, and he/she would like us to tell them what it is. Since the gem was going to be used for jewelry, we can rule out the obscure and very soft collector gems, and limit our scope to relatively common jewelry gems that come in vivid, transparent green. This leaves emerald, chrome diopside, Tsavorite garnet and tourmaline as the prime suspects. We are just getting our gemology laboratory off the ground, so all we have is some reference books, a hydrostatic weighing set up, and a set of heavy liquids. First, we'll do our SG test hydrostatically, then with the heavy liquids. We look up the SG ranges in our reference guides:

[Is it?: emerald (SG = 2.72 +.18/-.05); tourmaline (SG = 3.06 +.20/-.06); chrome diopside (SG = 3.29 +.11/-.07) or Tsavorite garnet (SG = 3.61 +.12/.04)] HYDROSTATIC TEST STEP ONE: WEIGH GEM IN AIR

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The weight in air is: 2.420 ct. STEP TWO: ASSEMBLE HYDROSTATIC WEIGHING CHAMBER AND "TARE" BALANCE

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The beaker with water is actually suspended by an arm off to the side and does not put weight on the balance pan, the plastic ring which holds a little metal basket for the gem, does put weight on the balance, though. Once everything is set up, we "tare" the balance (resetting it to zero) so that it ignores the weight of the plastic ring and gem basket. Now we are ready to place the gem in the basket where it will be weighed underwater. STEP THREE: WEIGH THE GEM IN WATER

The weight of the gem in water is: 1.615 ct. The difference between the weight in air and weight in water is: 2.420 ct - 1.615 ct = 0.805 ct STEP FOUR: CALCULATE SG SG = Wa/ Wa-Ww SG = 2.420 ct /0.805 ct = 3.01 Can we eliminate any possibilites? Check the SG range of each of the four possibilities. (Assume we have made accurate measurements and our arithmetic is correct).

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emerald (SG = 2.72 +.18/-.05); tourmaline (SG = 3.06 +.20/-.06); chrome diopside (SG = 3.29 +.11/-.07) or Tsavorite garnet (SG = 3.61 +.12/-.04) The only gem whose SG range does not exclude 3.01 is: tourmaline! The others are either too high or too low to qualify. **Pretty cool.** Testing by Heavy Liquids: Below are the results of the same test on the green gem, done with the set of heavy liquids: 3.32: gem floats rapidly 3.05 gem floats very slowly 2.67 gem sinks 2.62 gem sinks rapidly 2.52 gem sinks very rapidly

Based on these results, the conclusion we must draw is that the SG is below 3.05, and above 2.67 (but closer to 3.05). If this were the only available testing method, we would be able to eliminate the chrome diopside and the Tsavorite garnet, but we'd have to do some other tests to discriminate between emerald and tourmaline. Most gemologists prefer to use the hydrostatic method, not only because of its greater precision, but also because the heavy liquids smell very bad, and have hazardous properties such that gloves and masks must be worn when using them. HOMEMADE HEAVY LIQUID TEST FOR AMBER

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[A saturated solution of salt water with amber and plastic immersed] One fun, and safe, heavy liquid test that can be done at home uses a saturated saltwalter solution. (Make this by dissolving as much salt in room temperature distilled water as it will hold). The SG of this mini "Salt Lake" is about 1.13. Most types of natural amber will float in it (SG = 1.08) while nearly all the plastic materials used to make imitations of amber will sink as their SGs are higher than 1.13. Imitation amber is rampant in the gem marketplace (even in some of the better stores), so this is a handy trick to know. MISCELLANEOUS PHYSICAL PROPERTIES There is a very long list of esoteric physical properties which gemologists/physicists/crystallographers and others working in research labs can study and measure in gems and minerals. To finish up this section, though, I will mention just a few that have occasional usefulness for the ordinary gemologist or gem/jewelry lover, and that do not require high budget equipment. 1) Magnetism: Very few gems show any magnetic properties. One interesting exception is a certain type of synthetic diamond. In this case, a strong magnet can be a definitive way to separate these stones from natural diamonds. Natural hematite is mildly to moderately attracted to a magnet, but an imitation version is so strongly magnetic that the difference is obvious. 2) Thermal Reaction: The response to high temperature in terms of appearance, and especially odor, can be a telling one in identifying some gems. Many organic gems such as horn, ivory, tortoise shell, and black coral 74

smell like burning hair when touched with a "hot point" probe. Amber smells like turpentine, and jet like burning coal. Their common imitations may have odors, but not the right ones. Although, technically destructive, this test can usually be done on a very small, inconspicuous spot. Resin, lacquer and wax coatings on gems can likewise be detected as they melt or char under the hot point. In this case, the reaction is best observed under magnification, with the hot probe not touching the surface, but just barely above it. 3) Thermal Conductivity: Gems differ quite dramatically in this property, which is basically a measure of the rate at which they conduct applied heat. For many years no savvy jeweler or pawn shop owner would be caught without a thermal conductivity tester (otherwise known as a diamond tester). By simply touching a small metal probe to the gem, it was instantly determined to be "diamond" or "not diamond". Pretty useful, huh? Well, it used to be.... A few years ago, two developments occured which have all but made these devices obsolete. 1) A new diamond simulant, called Moissanite whose thermal conductivity is close enough to diamond to pass the test, has come on the market, and 2) synthetic diamonds are now becoming a common enough to be concerned about. Man-made diamonds which have the same physical properties as the natural gems, would, of course, pass the test as diamond. 4) Electrical Conductivity: Very quickly upon the heels of the introduction of Moissanite, came the marketing of a new generation of testers which use a different tactic to separate Moissanite from diamond. Diamonds (with the vanishingly rare exception of natural blue ones) do not conduct electricity, but Moissanite does. So, out with the old and in with the new generation of diamond testers. These machines have two systems, a thermal conductivity test, to first separate diamond and Moissanite from all other gems, then an electrical conductivity test to do the final separation should the thermal test indicate diamond. (Again, synthetic diamonds cannot be separated from natural ones with any basic physical tests).

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[Mizar DiamonNite Dual Tester: Image courtesy of www.Mineralab.com] Placing the probe on a gem initiates a thermal conductivity test to reveal CZ or other non-diamond simulants, then if the stone passes that, an electrical conductivity test follows to determine if it is diamond or Moissanite. Answers to thought exercises from this lesson: (If you don't understand why these are the correct answers, then it's time to email me for help!) 1) It is probably pink tourmaline, as tourmaline has no cleavage and Kunzite has two perfect cleavages. 2) You should choose the blue sapphire. Sapphire has no cleavage and blue topaz has perfect cleavage in one direction. 3) Very thin or pointed areas on a cut gem, like the tips of a marquis cut, are areas of weakness; since apatite has cleavage, it would be much safer in a shape with smooth curves like a round or oval. 4) Seeing a conchoidal fracture pattern on the edge of the broken piece would indicate that is not turquoise (or coral) whose fractures are granular and uneven, respectively, but it could very well be glass. 5) The 6 mm Smithsonite is quite a bit heavier than the same sized calcite. The one carat calcite is noticeably larger than the same weight Smithsonite. 6) The 6 mm aragonite is a bit heavier than the same sized calcite. The one carat calcite is slightly larger than the same weight aragonite. 7) Even if gold and platinum were equally priced per ounce, the amount of platinum required for a given size and shape ring would weigh more (because it is denser) making the platinum ring more expensive.

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You have now completed the web lecture for the third lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the non-graded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture.When you're ready, proceed on to Lesson Four: Optical Properties of Gems

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OPTICAL PROPERITES OF GEMS Optical properties are those which are related to the behavior of light, on, or in, a gemstone. Some of these can be seen, and even quantified, with the naked eye alone. Three such characteristics are: luster, transparency, and color. The study of these factors, and their use in gem identification and evaluation, is sometimes called optical gemology. Other characteristics are revealed, or measured, only through the use of special instruments. Some of these include: refractive index, optical character, birefringence, pleochroism, dispersion, reaction to ultraviolet light and selective absorption. When these properties of gems are analyzed and measured, one is engaging in laboratory gemology. Luster The luster of a gemstone is comprised of the quantity and quality of the light reflected from its surface. There is an inherent, potential luster possible for each species and variety of gemstone. The actual luster, on any individual piece, however; may be less than this, due to the skill level of the lapidary or facetor, the presence of inclusions, or various chemical or physical changes, such as oxidation or abrasion, that can affect the surface. The names, which have been given to the various lusters seen in gems, are derived from their resemblance to familiar surfaces. (The prefix subindicates "just less than".) Some lusters are so embodied by a particular stone, that its appearance is named for that stone, as in the case of adamantine luster (adamas = Greek for diamond), and pearly luster. Looking through either of your textbooks at the descriptions of the various gems will convince you that a substantial majority of gems have a glass-like or "vitreous" luster. Look at the picture of the fire agates below and compare what you see on their surfaces to that which you'd see on a freshly washed and dried drinking glass--> keeping that image in mind should help greatly in estimating the luster of a gem.

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[Pyrite (in shist): metallic; diamond: adamantine (like diamond); zircon: subadamantine; fire agate: vitreous (like glass)]

[Fluorite: subvitreous; nephrite jade: greasy; amber: resinous]

[Pearl: pearly; tiger'seye: silky; granite: dull] Transparency Technically known as "diaphaneity", the degree of transparency of a gemstone is one of its most directly observable and familiar characteristics. Transparency (or lack of it) is dependent on how much light gets through the gem, and is affected not only by the chemical and crystalline nature of the gem, but also by its thickness and, as in the case of luster, by inclusions, and its surface condition. In the discussion and examples that follow below, we will be looking at the "potential" maximum transparency of a species in general, rather than the actual transparency of any individual specimen. When light hits the surface of a gem, there are only three fates for it (with respect to transparency). Various portions of the total amount of light will be reflected, absorbed or transmitted. The proportion in each category will determine the transparency of that gem. 79

[Three fates for light hitting a gem: it can reflect (be returned) from the surface or interior of the gem, it can be absorbed by the gem, or it can be transmitted through the gem] Reflection: Light is reflected when it hits an exterior or interior surface of the gem and is bounced back off, or out of, the gem, in the direction of the observer. Absorption: When light enters a gem and does not exit, we say it has been absorbed. Light is a form of energy, and energy does not just disappear, instead the visible light has been converted to a non-visible form of energy, in most cases, heat. Transmission: Light that travels through the gem and exits in a direction other than that of the observer, is said to have been transmitted. The issue of transparency (with the factors of reflection, absorption and transmission) is actually more complex than it may seem at first, because it is intimately linked with the color characteristics of a gem. For the time being, however; we can be satisfied with the following descriptions: Opaque: No light is transmitted. Translucent: Some light is transmitted. Transparent: A high proportion of the light is transmitted. The term "semi" is sometimes added to describe intermediates, and gives additional categories beyond the basic three.

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[Citrine: transparent; Prehnite: semi-transparent; chrysoprase: translucent; sugilite: opaque] Within any particular species of gem, it is often the most transparent pieces which are the most valuable. For example, in chrysoprase, shown above, which is generally semi- to fully translucent, one finds occasional pieces that are semi-transparent. These are greatly admired and sell for higher prices. The same can be said of nephrite and jadeite jades where price (within the same color) can escalate dramatically based on nuances of transparency. Likewise, in gems that are usually opaque, like the sugilite pictured above, the occasional semi-translucent to translucent piece (called "gel sugilite"), is highly prized. Color The color of a gem is determined by selective absorption of some of the wavelengths of light. We know that what appears to us as white (or colorless) light is actually made up of light of various colors. Issac Newton was the first to demonstrate this back in the 17th century.

[Image courtesy of www.nasa.gov] Scientists in later years, were able to show that the color of light is a function of its wavelength. In the diagram above, a wave-form representation shows the relative distance from crest to crest (wavelength) of the various components of white light. Notice that these distances increase toward the red end of the spectrum and decrease toward the violet end. The wavelengths are very small, and we do not have everyday measurements to describe them. A nanometer (nm) is one billionth of a meter, and is an appropriately sized unit for this use. Using this terminology, then, the 81

portion of the electromagnetic energy spectrum which our eye and brain interpret as light, extends from approximately 700 nm on the long (red) end to about 400 nm on the short (violet) end. Visible Light Spectrum (nm) • • • • • •

700 - 630 = red 630 - 590 = orange 590 - 550 = yellow 550 - 490 = green 490 - 440 = blue 440 - 400 = violet

(For generations, students have been introduced to "Mr. Roy G. Biv", as a simple device for remembering the order of the colors in the light spectrum). Not to get too far afield from our subject matter, it is necessary to mention that this spectrum extends greatly on either side of the narrow visible range: into ultraviolet, xrays and gamma rays on the short end, and into infrared, microwaves and radiowaves on the long end. The little segment of it that we are concerned with in this class, not only powers vision, but also photosynthesis, and many other biologically relevant processes. It is also important to point out that the energy content of the various colors of light is related, in an inverse way, to their wavelength. That is, light of shorter wavelength is more energetic than light of longer wavelength. Selective Absorption: The color of most objects, gems included, is a result of a process called "selective absorption". Let's take an example: suppose you have on a yellow shirt--> Why is it yellow? The fibers and dyes in it absorb only some of the wavelengths of the white light that hits them, primarily in the red, orange, green, blue and violet bands. The wavelengths that are left (the yellow ones) are reflected back to the eye of the observer whose brain interprets light energy of that wavelength, as what we call yellow. I'm sure you can see how a shirt could be greenish yellow or orangey yellow if wavelengths slightly shorter or longer than yellow were also reflected, and red or blue if it had a quite different pattern of selective absorption. With opaque objects it is the color of reflected light that we see, with transparent and translucent ones, the color we see consists of a mix of both their reflected and transmitted wavelengths. Let's see if we can put together the information on transparency with that on color: 82

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Transparency will depend on the relative proportion of light reflected, transmitted and absorbed by a gem. The color of the gem will depend on what is reflected or transmitted after selective absorption has removed some portion of the spectrum. o If none of the wavelengths are absorbed: the gem will be colorless if it is transparent, or white if opaque. o If equal amounts of each wavelength are absorbed: the gem will be grey. o If all wavelengths are absorbed equally and completely: the gem will be black. o In colored gems: we will see a mix of wavelengths which were not absorbed and which (depending on reflectance vs transmittance) will give us a colored tranparent, translucent or opaque gem.

Ok, so selective absorption determines color, but what, then, determines selective absorption, you ask? That is, why, precisely, do rubies look red and sapphires look blue? The basic answer is simple, and two-fold, and goes right back to the basic point previously made in Lesson 3 regarding all gem properties. Selective absorption in gems is determined by an interplay between their chemical makeup, and their three dimensional structure. The atoms (or ions) which create color in a gem are called "chromophores". Some of the most common chromophores in gemstones are: atoms of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, nitrogen, and boron and their various ions. (A new, undefined term, "ion", has crept in here, so let's deal with that). Atoms are made of smaller particles: protons, neutrons and electrons. The protons have a positive charge (+) and the electrons a negative one (-). In an atom, such as oxygen, or iron, or any other, the number of protons and electrons are equal making it, overall, a neutral body. Suffice it to say, that chemical and physical events can, and do, occur that add or subtract electrons from atoms, making them into negatively or positively charged bodies called ions. Fe is the chemical symbol for a neutral iron atom, Fe+2 designates an iron ion (an atom of iron which has lost two of its electrons), Fe+3 has lost three, Cl- is a chlorine atom that has gained an electron, etc. The main point for you to understand is that events that occur in the "life" of gems and minerals (or in a gem enhancer's laboratory) can 83

change the ionic state of their constituent atoms and ions, and thereby affect their color. Back to the main point, the presence of various chromophores, as well as certain details of the three dimensional structure of the material itself, cause the selective absorption, which, in turn, causes color. To put it another way, both the presence of particular atoms and ions, as well as specific crytal "defects" such as missing atoms or extra ones, areas of compression or strain, can act as the agents of color in gems. Idiochromatic vs Allochromatic Gems With regard to the source of their color, gems fall into two categories: idiochromatic and allochromatic. Idiochromatic gems derive their color simply from the chemistry of their basic formula. Due to this fact, such gems will always occur in various shades of the same basic color. The other group (more common) are allochromatic, meaning that the chemistry of their basic formula does not cause any selective absorption so in the pure state, they are white or colorless. In gems of this sort it is tiny, trace amounts of impurities that act as the chromophores. Such gems occur in colorless forms as well as in a variety of other colors depending on the nature and amount of the "contaminants" in them. [I think you'd probably get an argument from someone who is admiring their beautiful blue sapphire, if you called the tiny amounts of titanium and iron that give it that color,"contaminants", though.] Some examples of idiochromatic gems are: peridot containing iron, (Fe), rhodochrosite with manganese (Mn) and cuprite and malachite containing copper (Cu). Idiochromatic Gems

[Peridot (Fe+2), rhodocrosite (Mn), cuprite (Cu+1), malachite (Cu+2)] Hey wait a minute, you say--> cuprite is red, malachite is green, and both contain copper! What gives? Welcome to the wonderful world of gem color! It is not quite as simple as: this element makes this color, and that element 84

makes another color. Each gem's color is determined by an interplay between its chemical makeup (including the ionic state of its chromophores) and its structure. To further pursue this point: some emeralds are green due to chromium content, while some get their green color from vanadium. So, iron (as in peridot), copper, chromium or vanadium can each be responsible for "greenness" in a gem. But on the other hand, chromium in corundum makes red rubies, and iron in chalcedony, makes orangey carnelian, but in sapphires gives us yellow. Futhermore, green zircons and green diamonds get their color not from chromophores, but from crystal defects. Allochromatic Gems Some examples of allochromatic gems are: beryl, corundum, quartz, grossular garnet, tourmaline, topaz, spinel and nephrite jade. In some cases the "pure" material is the most common and therefore the lowest in value (corundum, quartz, beryl and topaz are in this category); but in others, the pure form is so rare as to be a high value collector's item. This is especially true in the case of grossular garnet, tourmaline and nephrite jade. Colorless spinel is so rare that it literally has not been found in Nature; we know it can exist, though, because colorless synthetic spinel is made in labs. A good example of an allochromatic gem species is corundum. Pure Al2O3 is colorless, as in white sapphire, but if we add just a tiny bit of iron to the mix then we get yellow or orange fancy sapphire, pair the iron with a bit of titanium, and the gem is the familiar blue, and if chromium is the chromophore, then the corundum is red and called ruby. Allochromatic Gems (in their pure state)

[Colorless beryl (Goshenite); "white" sapphire, colorless quartz (rock crystal); colorless grossular garnet (leucogarnet)] Allochromatic Gems (in their impure state)

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[Beryl: emerald (chromium or vanadium); corundum: sapphire (titanium and iron); quartz: carnelian (iron); garnet: Spessartite (manganese)] Other Sources of Color: Some gems get their color (or apparent color) from visible to microscopic inclusions of other minerals within them. One of the most beautiful of all the chalcedonies, often called "gem silica" but more properly termed "chrysocolla chalcedony" has a vivid blue-green color. The minute quartz crystals are actually colorless, but in amongst them are tiny crystals of the blue green (very soft) mineral, chrysocolla. The overall impression, in the best specimens, is a translucent chrysocolla colored gem, with the durabililty of quartz. In the varieties known variously as strawberry and raspberry quartzes, visible particles of red or red-orange hematite in the colorless quartz, create a pink, orangey, red or polkadot looking gem, depending on their size and number. Inclusions

[Chrysocolla quartz, strawberry quartz] Patterns in color: banding/zoning One of the most common features of some of the aggregate gems is the presence of patterning. Since these gems are formed from very tiny single crystals, we can easily envision conditions where differently colored pools or batches of tiny crystals mix and intermesh creating bands, dots or other patterns. Agates and jaspers are the most commonly seen gems with strong patterns. It frequently happens that single crystal gems subjected to changing conditions during their growth can also show bands or zones of different colors or shades of the same color. When these are dramatic and attractive, 86

they are desirable, but far more commonly, gems of this type have nondescript, patchy, or zoned coloration, and are considered inferior to more evenly colored pieces. Aggregates With Patterns

[Zebra agate, picture jasper, Mookaite jasper, carnelian, lavendar agate, Dalmation jasper, rain forest jasper] Single Crystal Gems with Attractive Color Zoning

[Ametrine, multi-color tourmaline, watermelon tourmaline] Color Descriptions in Colored Gemstones There are three aspects to a formal colored stone color description: hue, tone, and saturation. Using these three descriptors, very detailed and nuanced color discriminations can be made, and communicated, between gemologists, jewelers and gem buyers. Let's take them each in turn: Hue: The hue of a gem is its basic position in the color spectrum: red, orange, yellow, green, blue or violet--> but it also includes all the possible intermediates like slightly yellowish orange, or moderately bluish green. Tone: The tone of a gem, basically how light or dark the color, is independent of its hue and ranges from so light as to appear virtually colorless, to so dark as to look black. 87

Saturation: The least commonly quantified aspect of gem color is "saturation", which is a measure of the purity of color, that is, the relative presence or absense of modifying grey or brown hues. It turns out that in most cases, as long as the hue and tone are reasonably nice, it is the degree of saturation of color that is the prime value setter in gemstones. You might ask, why does color description need to be so formalized? The main reasons are listed below: •

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Small color differences mean big dollars!: in the rarified world of gem and jewelry connoisseurs, zeros can be added to prices based on what look like small differences in color to the rest of us. Commonly used adjectives are subjective, and culturally based: Without some system of regularizing color descriptions it is very difficult to communicate color information efficiently. o For example: Give three of your friends a unlabeled color chart and ask them to show you "royal blue" or "lime green", or medium orange. I can guarantee you'll get three noticeably different color choices from each of them. Additionally, limes may not be a familiar fruit in the country where you wish to purchase a gem, or royalty there may be associated with yellow, not blue. Color memory is notoriously unreliable. Without a system whereby precise color coordinates can be recorded, there is little chance of doing a good job matching a new piece to an existing one. o A couple of simple exercises can verify this statement: You have a nice sunny yellow paint in the kitchen, but some of it is chipped off and needs repair. You go to the paint store and pick the color from the paint charts that matches the color in your memory--> what are the chances it will, in fact, match? Or, let's say you want to buy a new shirt to match your favorite brown pants: good luck, if you don't wear or take those pants with you when you go shirt shopping! GIA Color Description/Grading System

One well done, and widely used, system for color description is that developed and taught by GIA (Gemological Institute of America). Although 88

not universal, it is familiar world-wide, and the basis for most formal gem description and evaluation in the US and Europe. Since the wavelengths and light colors grade into one another in infinitesimal changes, there are an essentially infinite number of hues which could potentially be described. Most of these hues would be indistinguishable from each other to our eyes, so GIA has settled on a group of 31 which humans with normal color vision (and some training) can discriminate. The set of plastic gem models below is a representation of those 31. (It should be noted that GIA has taken some liberties with the traditional "Roy G. Biv" spectral colors, deleting indigo, and adding purple after violet. In the set below, then, you see: red, orange, yellow, green, blue, violet and purple. The intermediates are described by terms like slightly, moderately and strongly to indicate a spectral hue modified to various degrees by those on either side of it on the spectrum. It also recognizes hues which are exactly 50/50 mixes such as red-orange and blue-green. HUE

[Gia's 31 basic gem hues] The hue, then, consists of the key (or spectral) color plus adjectives describing the hue and strength of the secondary modifying color, if any. For example: slightly purplish red, symbolized by "sl p R" (sl for degree, lowercase p for the secondary hue (purple), and upper case R for the 89

primary hue, (red). The description strongly yellowish green: "st y G" would be decoded using the same logic. Once you have been trained to see nuances of color, you recognize that pure spectral colors in gems are quite rare, and as a result, costly. For example: a hue of simply "B" would be pure spectral blue and if other factors of color and clarity were good, the piece would command a premium price. If you are thinking that it looks like there are more gradations in the blues and greens in the display above, than in the other colors, you are right. Human vision has finer powers of color discrimination in that part of the spectrum, which this system takes into account. TONE Each of the 31 hues exists in a range of tones from almost colorless to almost black. GIA labels the tones as 0 - 10. {0 ( appears colorless), 1 (extremely light,) 2 (very light), 3 (light), 4 (medium light), 5 (medium), 6 (medium dark), 7 (dark), 8 (very dark), 9 (extremely dark), 10 (appears black). The figure below represents the 2-8 part of that range, which is, in the great majority of cases, the range for marketable colored gems. For most species the most valuable tones are in the 5-6 range. The set below is shown without hue, and it takes practice and patience for the would-be colored gem grader to learn to superimpose hue onto these, and get a valid tone reading. An additional complication comes from the fact that gem species differ in their inherent tone ranges. For example, let's compare an aquamarine and a pyrope garnet each of tone 6. Objectively, each is exactly the same, but that depth of color is about the deepest that will ever be found for aquamarine and the about lightest possible for any pyrope. One should not be surprised, then, to find the aqua dealer calling her stone "very dark" and the garnet seller raving about how beautifully light his stone is when they are both "6"'s.

[GIA's tone scale from 2 (very light) to 8 (very dark)] 90

SATURATION Finally, it's time to examine the most subtle aspect of gem color, saturation: in a manner of speaking, this measure is the degree to which the other spectral colors "muddy up" the main hue. Think of a can of pure red paint and start adding in various amounts of all the other colors--> the more you add of the other spectral hues, the "browner" the red will get. Now do the same thing with a can of pure blue: the more you add the "greyer" the blue will get. In general, desaturating "warm colors" makes them look brownish while the same effect in "cool" colors looks more grey. Therefore, GIA's system of describing saturation makes a distinction between cool and warm hues. Warm hues = green through red (desaturated to brown) Cool hues = purple through blue (desaturated to grey) Six degrees are recognized ranging from: 1 (brownish/greyish), 2 (slightly brownish/greyish), 3 (very slightly brownish/greyish), 4 (moderately strong), 5 (strong), 6 (vivid) **In the figures below, you can get a better idea of the saturation effect by looking at the flat end of the plastic gem replica, rather than the "gem part".

[GIA's six degrees of warm hue saturation]

[GIA's six degrees of cool hue saturation] 91

When giving a gem's formal color description in words, then, the gem below might be said to be: medium dark, slightly greyish, blue-violet. It sounds more natural to put the tone, saturation and hue in that order. In a numeric description as required in offical gem grading documents, however: the order would be: hue, tone and saturation, thus: BV 6/2

[Iolite: in words: medium dark, slightly greyish, blue-violet = official "grade": BV 6/2] One final point on the GIA color grading scheme: Two non-spectral colors are used (in addition to the officially sanctioned 31) and those are pink (pk) and brown (br). If one were to strictly follow the GIA system, all shades of pink are really lighter tones of red, and brown is simply desaturated orange. It is rather a matter of bowing to tradition and convenience to recognize pink and brown as "colors" in their own right. You will see evidence of this practice in the color description below.

[Spinel: medium dark, moderately orangey, strong pink--> mod o PK 6/5] Color Grading in Diamonds You will recall from Lesson 1 that within the gem industry, there are separate systems for marketing, grading, and describing colored gemstones and diamonds. For virtually all natural diamonds, discernable color is a negative attribute. The closer it is to an absolutely colorless condition, the more highly valued is the gem. In the case of what are called "fancy" diamonds, whose color is both intense enough, and attractive enough, to be desirable, color is described and evaluated in a similar manner to that used for colored stones. There is sort of a "U" shaped value curve for diamonds, whereby the highest values accrue to only the whitest, and then, again, to the most vividly colored 92

specimens, with value bottoming out in the central ranges where there is just a bit, to a moderate amount, of color. Although most of the diamonds you might see on a day-to-day basis are called "white" and appear so, a little study and comparison will verify that a truly colorless diamond is a thing of great rarity, and the vast majority of diamond gems are actually tinted with small but noticeable amounts of yellow or brown. I was taking some liberties, perhaps, by using the GIA system in the preceding discussion of colored gem descriptions, but without doubt, the GIA system is the one to learn if you are interested in diamond colors and value. It is understood everywhere in the world, and used for formal grading in most countries. Even competing gem grading laboratories either use the GIA system, or provide a key to translate theirs to it. For example AGS, The American Gem Society uses 0 - 10 for their color grading scale (0 = D, 0.5 = E, 9.5 = W, 10 = X - Z, etc.), but gives the customer an exact conversion scale to the GIA system with their reports. Before the GIA system was developed (beginning in the 1930's), there were as many diamond color descriptions as there were diamond sellers. Many of them used A, B, C and A+, AA, AAA etc. while others used adjectives like "river" and "cape". It is easy to see how difficult it would be to have a reliable system for trade under those conditions. GIA's scale did away with A, B and C because of their long histories and diverse useages, and developed a system based on color grades from D-Z for "colorless" stones, plus the term "fancy" to indicate those whose strong color made them more, rather than less, valuable. What the Letters Mean D, E, F: gems in this range appear colorless even in larger sizes, only a highly trained diamond grader can tell the differences between them. G, H, I: these grades describe gems that look colorless to most viewers in smaller sizes and if mounted. J, K, L: small and mounted stones of these grades look near colorless, but larger and unset gems begin to have noticeable color M-Z: gems in this range are worth much less than higher color grades and range from some color noticeable to distinctly light yellow (or brown). 93

Z+: beyond Z is the range of the "fancy" diamonds whose value is based on their hue tone and saturation, as in colored stones. In general browns are least valuable with yellow, orange, and green worth considerably more. The pinnacle of value for naturally colored diamonds is occupied by purple, blue, pink, and at the very tip-top, red. The images below may or may not be enlightening, based on the characteristics of your vision, viewing circumstances, and monitor calibration, but they will hopefully serve to illustrate at least some of the aspects of our topic.

[Image courtesy of www.yourgemologist.com]

[Image courtesy of R.F. Moeller, Jewelers] How Do they Do That? After straining your eyes to see the minute changes in the illustrations above, you might ask, how can a grader do it, especially when a great deal of money rides on the difference between, say an F and a G grade, or an L and an M? I might joke that the answer is "verrrry, carefully". In actuality, not everyone can become a successful diamond grader--> there is both exacting training and "raw talent" involved. In practical terms, the mechanics of the process is that the stones to be color graded are serially compared to the gems in a special "master stone" set, under controlled conditions of lighting and viewing. Gemology: Then and Now Pre-modern: What we could refer to as modern-style gemology began and developed in the period between 1930 to 1950. Prior to that time gemology was a simpler discipline to master and practice than it is today. The mains reasons for this are: •

Relatively few gem species and mining locales were known. Although gem exploration was certainly engaged in, the 94

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scale was much more limited, and as a result there were but a few dozen known species and varieties of gems, and a correspondingly small set of mine sites. The tools of the trade were limited. A magnifier, a hardness testers, some acid for detecting carbonates, and balances for determining specific gravity were all that was in the gemologists' kit. We might say that practicioners of earlier eras were "optical gemologists". Most of the gems' measurable properties were either physical (density, hardness, stability, crystal habit) or those which could be seen with the naked eye, such as, luster and color. Relatively few enhancement processes existed. Heating, dyeing and coating were long-familiar techniques which for the most part were easy for a trained eye to detect. Synthetics and simulants were few. Only a handful of gems had been synthesized prior to 1950 and those had clear cut signs indicating their "non-natural" origin. Simulants were common, but they were mostly either assembled gems, or natural substitutes, which, again, were relatively easy to detect with the knowledge and equipment of the day. To give an example, I'll relate a true story: Recently, a client came to a gemologist I know, with an antique ring that they had inherited. Along with the ring was a jeweler's certificate, dated 1870, certifying that the gem was an emerald. A variety of tests soon revealed that the stone was, in fact, a green tourmaline. Had the client's ancestor been duped by an unscrupulous jeweler? Most likely not. With the tools and knowledge available in the 1870's, a green stone of hardness greater than 7, and with a vitreous luster that came from South America (as this one did) would have been called an emerald. Thus it is, that a lot of the "rubies" in museum collections are actually red spinels, and much of the "jade" pieces among the displayed artifacts are serpentine or hydrogrossular garnet.

Gemology Today: Today's gemology is a very different sort of game--> I say "game" because it has quite literally become a tug of war, or an "arms race", if you will, between gemologists and those who seek to profit from misinformation or ignorance. In comparison with the list above we find:

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There are now hundreds of recognized gem varieties and species, and the rate of discovery of them is increasing. The world's hunger, and willingness to pay dearly, for gems has fueled an unprecidented rate of exploration for new sources of both colored stones and diamonds. As an example: a new species in the beryl group of gems was identified in 2002. The discovery of new varieties, and new sources for known varieties, happens very frequently, but a completely unknown species of gem mineral, is as big a piece of news to the gemological/mineralogical world as a new species of mammal or bird would be to the world of biology.

[Pezzottaite a new cesium rich species of beryl, discovered in Madagascar, cat'seye stone, uncut crystal] Check the web: Look here for more detail on the properties and discovery of this species: http://www.mindat.org/min-25652.html •

It is very common for different mine sites with different geological histories to yield the same variety of gem, but with slightly different chemistries and inclusions. Because identification often depends on subtle nuances of inclusions and/or chemistry, the definitions and identification criteria must constantly be modified to reflect and incorporate these new discoveries. To give a fairly dramatic example: until the 1960's an emerald, by definition, was beryl of medium to medium dark, strong to vivid slightly bluish to slightly yellowish green, colored by the element chromium. The discovery of African beryls which looked like emeralds but contained vanadium rather than chromium, led to vigorous (some would say bloody) debate, that culminated in changing the official definition of an emerald (to include vanadium as a possible chromophore). It also made the use of a standard gemological tool, the Chelsea filter, which reveals the 96

presence of chromium, pretty much obsolete for its, then, major purpose of separating emerald from most of its simulants. •

Enhancements have become huge business, and the temptation NOT to disclose them is as large as ever. Very sophisticated techniques of heating, dyeing, coating, stabilizing and irradiating have been, and are being, developed. These require ever more knowledge, and equipment on the part of the gemologist or gemological laboratory. The best recent example of this is the sudden appearance on the market around the year 2000 of an abnormal quantity of the rare "padparashah" variety of fancy sapphire (its color is pink/orange). Initially, collectors rushed to grab the abundance, as such opportunities are generally very transitory. The enriched supply continued, though, and increased--> raising the suspicions of gem dealers and gemologists world wide, and sending them scurrying to the field, and to their laboratories. It turns out that a brand new, very difficult to detect, type of enhancement, called "beryllium diffusion" was the culprit. The news stunned the gem world in 2002, and made the gem treaters who sold these bogus stones wealthy, in the short period before they were found out.

[Beryllium diffused, enhanced "padparashah" sapphire] •

Last, but to be sure, one of the most important new developments, has been the introduction of multiple new technologies for synthesizing gems. The easy to detect early methods are still being used, but an increasing percentage of high (and even lower) value gems are being synthesized by methods that so closely simulate natural formation conditions, that the gems they produce require extreme vigilance, and ever more sophisticated analyses to reveal. 97

Thus, today's gemologists, as much as those in any other rapidly advancing area of science, must constantly watch the literature, and keep themselves abreast of any new tools or techniques which they can use to keep "one step ahead" of those who would deceive. As we turn our attention to laboratory gemology, we'll be looking at several basic properties or "behaviors" of light and seeing how each, in turn, is useful in describing gemstones. The aim of this part of the lesson is to acquaint you with first, the basic facts of these properties, and subsequently show how they are measured, and/or how they can be used to solve problems in gem identity. Behavior of Light 1: Refraction We all know that the "speed of light" is the stuff of which cosmic measurements are made, and you may or may not have that famous figure in your store of readily retrieved facts. When we discuss the speed of light in an astronomical context we are thinking of the speed of light in a vacuum (the absense of matter), but light slows down when it travels through any medium denser than a vacuum. Air is not a vacuum, so light slows as it enters our atmosphere from space, in the same way, light slows from its "air speed" when it enters any material of greater density than air, which would include all gemstones. If a light ray enters the gem at any angle, other than directly perpendicular, to a surface, then it also bends as it slows. The degree of slowing is determined by the density of gem, and the degree of bending is determined both by density and by the angle of its entry. The ratio of the speed of light in air, to the speed of light in a gem, is called the gem's refractive index or RI. It differs, sometimes dramatically, between gem species, and is one of the most useful gem identification criteria. In natural gems it ranges from about 1.2 to 2.6. and can, in most cases, be measured by an instrument called a refractometer.

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[Refraction includes the slowing and the (usually) consequent bending of light as it enters a gem] Behavior of Light 2: Dispersion Dispersion (sometimes called "fire"), is the separation of white light into its spectral colors. It may be observed as specks of red, blue or green which flicker as the gem is turned. The cause of this phenomenon is the differential refraction (bending) of the various wavelengths of light as they travel through a gem. Red (long wavelength) bends less, violet (shorter wavelength) bends more. This causes the colors to become separated. Although dispersion, theoretically, occurs in all gems, the degree depends on the RI of the gem material, and only those gems with sufficiently high RIs, have dispersion which is pronounced enough to be actually visible. The exact figures for dispersion can be painstakingly measured in a laboratory setting using special equipment, and then calculated as the difference between the RIs of red light and violet light in a given species. Potential dispersion in gems, thusly measured, ranges from .007 to .280. Outside the lab, dispersion is generally judged visually, without instruments, simply as: absent, slight, moderate, strong or very strong. The degree of visible dispersion is affected by species (due to RI), but also by the body color, and cut proportions of the gem. In general, the denser the gem, the greater its potential dispersion. Light body color, and steep crown angles enhance the display, whereas dark body color and shallow crown angles diminish it. 99

[Dispersion of white light as it leaves a gem] Examples of gems with slight dispersion potential are: fluorite (.007), common glass ("crown" or silica glass) (.010), and quartz (.013). Regardless of color or cut, these gems just aren't going to show visible dispersion, the effect is too slight. Those with moderate potential for dispersion include: tourmaline (.017), corundum (.018) and spinel (.020). Such gems rarely show visible dispersion, but an occasional light colored specimen of substantial size with very high crown angles may do so. Examples of strongly dispersive gems are: zircon (.038), diamond and Benitoite ( both .044), and cubic zirconia (a synthetic), (.066). Gems in this range will usually show dispersion. Exceptions might be those of very dark body color, or small pieces cut with rather low crown angles. Very strongly dispersive gems include: sphalerite (.156), strontium titanite (a synthetic) (.190) and synthetic rutile (.280). There would be very few cases where a gem in this group did not show substantial dispersion.

[Benitoite and sphalerite both with cuts and body colors which permit their substantial dispersion to show]

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[Diamond a gem admired for its dispersion] Diamond is the most well known gem that shows dispersion, and it is one of that gem's most appealing attributes. The success of either a natural or manmade diamond simulant, depends to a large extent on how well the substitute matches diamond in this characteristic. Before the post-1950's crop of synthetic diamond simulants came on the market, the choices were limited to glass, foil-backed glass, or amongst crystalline gems: white sapphire, white beryl, white topaz or white zircon. Of that group, zircon made the best simulant due to its dispersion being much closer to that of diamond than any of the others. Quite a few synthetics have been created since then, but, only one, like the Baby Bear's porridge, is "just right" and that is cubic zirconia. Even though its dispersion figures are a bit too high, in the small sizes usually encountered, the difference is not obvious. YAG on the other hand is without noticeable dispersion and looks very "glassy", while synthetic rutile and strontium titanite have way too much to look convincing. The first set of pictures below shows, respectively, the two most convincing natural and man-made simulants. The second set shows a group of three temporarily popular, but unconvincing synthetics.

[Successful simulants: white zircon (natural) and synthetic cubic zirconia--> just about the right amount of dispersion]

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[Unconvincing simulants: YAG, (too little) sythetic rutile and strontium titanite (too much)]

Behavior of Light 3: Light is Influenced by the Optic Character of a Gem There are two groups of gems with regard to light refraction, each is said to have a different "optic character": SR or DR. SR stands for singly refractive. In such gems, each beam of light entering the gem stays as a single beam which has a single refractive index (travels at the same speed), regardless of the direction from which it enters. In this group we find all amorphous gem materials, such as opal, glass, amber, etc. as well as all crystalline gems belonging to the cubic (isometric) system. The most commonly encountered gems of the cubic system are: diamond, garnet and spinel.

[Gems whose optic charcter is SR: diamond, garnet and spinel (cubic system), opal (amorphous)] DR stands for doubly refractive. In such gems, single beams of light upon entering the gem, are split into two separate beams, which then travel perpendicularly to each other. Each of the resultant beams takes a different path through the crystal and, consequently, has its own speed. Such gems, then, have two RIs, one for each half of the original beam. In this group are all the gems of the non-cubic crystal systems.

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[DR gems: amblygonite (triclinic), citrine quartz (trigonal), pearl (orthorhombic), scheelite (tetragonal)] Important Note! Each DR gem, based on details of its crystal structure, has either one or two directions in which the light entering it behaves as if the gem is SR. These directions are known as "optic axes". Those species with a single optic axis are known as "uniaxial" and those with two are, logically, called "biaxial". It is sufficient to simply note this at present, but we will return to this fact and see that the existence of optic axes can constrain the methods by which we test some of the optical properties of gems, as well as serve as a valuable identification criterion in its own right. Birefringence: BR* Birefringence, a property of DR gems only, is measured as the difference between the high and low RIs of the split beams. It ranges from a low of .003 to a high of .287. When a transparent gem with high BR is faceted, and the view through the table direction of that gem is not in an optic axis direction, the slightly "out of sync" light beams can create an appearance of interior "fuzziness" or in larger stones, can show up as two distinct images of each facet edge. This is known as "facet doubling" and it can be a pain in the neck to a facetor who, in trying to prevent it, must find an optic axis direction for the table of the stone. But it can also be a valuable identifying characteristic that can often be seen with the naked eye or a simple 10x loupe. * For reasons unknown to me (perhaps it is a "British-ism"), the Hall text abbreviates birefrigence as "DR" in the tables at the back of the book and on the individual species pages. BR as used in this lecture, is the standard abbreviation used in most books.

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[Gems with high BR, showing facet doubling: calcite, synthetic Moissanite] The pictures below demonstrate the effect very clearly. The material below has been cut into a geometric form known as a "cuboctahedron" from synthetic rutile (which has extreme birefringence = .287). It has been placed above a single black ink dot on the surface. The left photo shows the view through the central face which has been cut on an optic axis. Note that the dot is clearly visible as "one" as are the reflections of its image in the other faces. In the second photo the piece of rutile has been turned so that we view the dot through another of its faces (one not on an optic axis). Now we see two images of the dot.

[Synthetic rutile above a single black dot: viewed in the optic axis direction, viewed in a non-optic axis direction: Images courtesy of Dr. Brad Amos] Food for thought: The newest diamond simulant on the market is called Moissanite. (That's the one that required the new generation of electrical conductivity testers discussed in Lesson 3). Fact: Moissanite is markedly birefringent; diamond, being SR, has no birefrigence.(Answers to the questions will be found at the end of the lesson) Question 1: When the sellers of Moissanite send their pieces of rough to be cut, they are very careful to mark the optic axis direction on each piece. Why? Question 2: Your friend shows you his new "diamond" ring. You look down through the table and you see no doubled facets. You take out your loupe (magnifier) and turn the gem at an angle so that you are not viewing straight

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through the table, and when you look at the stone, you see doubled images of all the facets. Could this be a diamond? Could it be a Moissanite? Behavior of Light 4: Pleochroism As we know, DR gems split light into two perpendicular rays, each taking different paths through the crystal: one ramification of this is birefringence, another is pleochroism. Pleochroism is the property of DR gems which results in their showing different colors, or different shades of the same color, when viewed in different crystal axis directions. How can this be? Think again of the crystal lattice of a DR gem, made of carefully laid out atoms of the gem's component elements (and the trace chromophore elements), with fixed distances and densities that can vary depending on direction. If two beams of light take a different path through this lattice, they may then be affected differently by selective absorption and emerge with different colors. This effect can be weak, moderate or strong, depending on the species of gem, the colors involved, and also on the color tone of the particular piece. A very light piece of a pleochroic species will show the effect less clearly than a more richly colored one. Unless the effect is extreme (as it is in iolite and Andalusite), we generally do not see it in a cut gem, because the bouncing and mixing of the light caused by the internal reflections from facets and edges blends the colors together and obscures it. Dichroic gems (like corundum) show two different colors while trichroic gems (like iolite) show three. Pleochroism will not be observed in SR gems, nor in DR gems when looking through an optic axis direction. In most cases, pleochroism can best be observed using an instrument called a dichroscope. This cleverly made little tool uses a piece of highly birefringent colorless calcite to split the incoming light into two beams which are bounced off tiny mirrors positioned inside so as to reflect each of the two beams onto a pair of side-by-side viewing windows. This placement allows the viewer to simultaneously see light that has traveled two different paths through the gem or crystal being viewed. Simultaneous viewing isn't absolutely necessary, but considering that these effects are often subtle and color memory is poor, it is certainly easier that way. All that is necessary to

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use this instrument is a good light source, and a transparent to translucent gem. Below you see a dichroscope (about 2" long) and a simulated view of a ruby gemstone, as it would appear through the dichroscope. For the sake of clarity I have emphasized the color differences, but they are not quite so distinct in reality. Ruby has an orangey red color axis, and a purplish red color axis.

[Calcite dichroscope, simulated view of ruby's characteristic pleochroism as it would appear looking through a dichroscope] One must view the gem being tested with the dichroscope from several different directions because: 1) Some directions will be optic axis directions, in which there would be no pleochroism shown, even if the gem were pleochroic. So, if you based your conclusion on one direction only, there would be a large chance for error. 2) Only two colors show at a time, so, although dichroism might be detected from a single directional view, it would take more than one to see all three colors in a trichroic stone. When strong, pleochroism may complicate the orientation process for a cutter and/or create setting issues for a jeweler. The cutter is going to want the most desirable or attractive color to be that seen when looking through the gem's table. For example, iolite has a lovely blue-violet axis, one that is grey, and a third that is a near colorless light yellow. Few buyers are interested in a grey or nearly colorless iolite. A large number of tourmaline stones have one axis that is an opaque black! The other directions may show a lovely green or pink, but if the gem is not cut so as to prevent light bouncing from the black direction into the green or pink, the color in the finished stone will look terrible--> a muddy brown. To prevent this, a special "tourmaline cut" has been devised whereby the sides of the offending axis are cut so steep (approximately 70 degrees) that light 106

from it is prevented from reflecting back into the gem. This leaves a gem with proportions that do not fit into standard prong or bezel mounts. Jewelers have had to devise a special "tourmaline mount" (as seen below) to accomodate such gems.

[Pleochroic Gems: an iolite showing a lot of its undesirable grey axis, an iolite oriented to show a near ideal blue-violet, a "tourmaline cut" gem mounted in a "tourmaline mount"] Tanzanite gems, which in the rough are trichroic, but after their standard heating process become dichroic, have a blue and a purple axis. Blue stones have a higher per carat value than purple ones, but, unfortunately, the shape of this gem's crystals dictate that the greatest yield comes from cutting a purple gem. The cutter, then, must balance these two factors and try to orient the stone so as to give the largest, best colored, and most valuable stone from an individual piece of rough. In some gems, most notably Andalusite, all the colors are attractive (brownish shades of green, red and yellow) and the mix of them in the finished gem is considered desirable.

[Pleochroic Gems: a Tanzanite with the purple color dominating, a Tanzanite with the blue color dominating, Andalusite showing patches of all its colors.] Check the web: For a neat web page discussing the use of a dichroscope by a professional facetor, look here:http://www.faceters.com/askjeff/answer36.shtml Food for thought: The tools you have are limited to a dichroscope and a gem reference book that lists the pleochroic colors of gems. You find that iolite is trichroic, sapphire is dichroic and spinel, which is SR, shows no pleochroism. You find that ruby is dichroic and, garnet being cubic, and 107

glass being amorphous, are SR and have no dichroism. You have no other equipment. Question 3: You have three blue transparent gems: an iolite, a spinel, and a sapphire, but they have no labels on them. Can you find the spinel? Can you separate the iolite from the sapphire? How? Question 4: You have three red transparent gems, also without labels: a piece of glass, a ruby and a garnet. Can you find the ruby? Can you separate the glass from the garnet with your dichroscope? Behavior of Light 5: Polarity of Light and the Optic Character of Gems The rays of light from the environment or from standard man-made sources are vibrating in all directions perpendicular to their individual directions of propagation. They are said to be non-polarized. With respect to this vibration, light is affected by the gem materials it enters in two possible ways: With DR materials, each of the two light rays that result from the splitting of an original beam, now vibrates in only one plane: it is said to be "plane polarized". Light goes into the gem non-polarized and comes out polarized. (The exception is light that travels through such a gem in an optic axis direction.) When we talk about such a pair of polarized rays, it is convenient to call one the E/W ray (East/West) and the other the N/S ray (North/South). SR materials have no such effect, the light remains non-polarized as it travels through the gem. That is, light goes in and comes out of the gem nonpolarized. We can also picture this by saying that light comes into the gem vibrating in all directions and exits the same way. This property is one that is useful in gem identification and can be readily detected with an instrument called a polariscope.

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[The effect of optic character on the polarization of light] Brief Review of SR -vs- DR Gems In singly refractive (SR) gems, light which enters remains as non-polarized beams, and travels through all crystal directions at the same speed. There is one refractive index (RI), no birefringence and no pleochroism. The SR gems can be amorphous or those of the cubic crystal system. In doubly refractive (DR) gems, light which enters splits into two perpendicular polarized beams. Each beam travels at its own speed and has a separate RI which depends on direction. Such gems have birefringence and may show pleochroism. A DR gem can belong to any crystal system, other than cubic. All DR gems have either one (uniaxial) or two (biaxial) optic axis directions in which they will behave as SR. Hint: when it comes to crystalline gems, if you commit diamond, garnet and spinel to memory as SR, then virtually all other crystalline gems you are likely to run into are DR. So, what is the optic character of topaz? amethyst?

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enstatite? diopside? etc. etc. Easy: Are they diamond, garnet or spinel--> No!, then they are DR. Food for Thought: Question 5: In the hint above, why did I stipulate "crystalline gems"? Testing for Optic Character

[A polariscope] The easiest way to test a gem for optic character is by using a polariscope. It is composed of two polarizing lenses with a light source below them. Each lens transmits only light that vibrates in single plane, either N/S or E/W. When the light in the base is turned on, normal, unpolarized light is produced, which becomes polarized, let's say N/S, as it passes through the lower polarizer on the base of the unit. The upper lens can be rotated freely. If the upper lens is parallel to the lower one (also N/S), then the light travels through it, and we see a lighted field. The picture below is a photo taken looking into the upper lens as just described.

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[Polariscope in the "open filters" position] If the upper lens is rotated 90 degrees, the N/S polarized light passed by the lower lens is blocked by the, now, E/W position of the upper lens. The view through a polariscope in this "crossed filters" position is shown below:

[Polariscope in the "crossed filters" position] The DR Reaction: Imagine taking a DR gem and placing it on top of the lower lens when the filters are in the crossed position. Since a DR gem actually functions as a small polarizing lens--> it now becomes a, third or middle, polarizer. Each 90 degree turn we give the gem changes the polarity of the light that goes through it, E/W to N/S, and vice versa. With one 90 degree turn, light that was blocked before can now get through, and we see the gem brightly lit. Turn it 90 degrees more--> the stone blinks dark as now it is producing light of the opposite polarization. This reaction, dark, light, dark, light is that which is characteristic of DR stones. The SR Reaction: Much less impressive, but equally telling is the reaction of an SR gem. Put an SR gem on the bottom filter (with the polariscope in the 111

crossed filters position) and it looks dark. Turn it 90 degrees--> still dark. No matter which direction you turn it, it is always dark. This type of material does NOT act as a polarizing lens and therefore doesn't change the polarity of the light that goes through it. It is logical for you to expect that since a polariscope tells the optic character of a gem, it should show either a reaction of either SR or DR when a gem is tested. Both SR and DR readings are possible, as described above, but there is a also a third possibility. Certain gems, when tested as described above, neither blink dark and light, nor stay dark. They are light as intially viewed and stay light no matter how they are turned!... What is going on? A gem with this reaction is an aggregate. (Remember, an aggregate is a gem made up of microscopic to sub-microscopic crystals all intermeshed together. Examples are various chalcedonies and jade). The AGG Reaction: All commonly used gem aggregates are DR, that is, the teeny tiny little individual crystals making them up are DR. But these little crystals are randomly oriented within the piece of material, so that on average no matter which way you turn the piece, about half of them are in their E/W position and half in their N/S orientation. Thus, turning the gem has no effect, a good amount of light is passed through it in any position. This reaction is called AGG. All of the above is MUCH harder to put into words, or to read and comprehend, than it is to observe and recognize. Let's do some tests. In the picture below are three pieces of gem material. One is quartz, one is glass and one is chalcedony. We'll observe their reactions under the polariscope and see what we can conclude.

[Items to test: one is chalcedony, one glass and one quartz] Specimen # 1: The first piece to be tested is the colorless one on the upper left. See its reaction below: (Note that you can, by looking at its shape, 112

determine which of the three pieces it is, and that it has been rotated approximately 90 degrees in the second picture.)

[Specimen #1 under "crossed filters" in two positions] Specimen # 2: The next piece to be tested is the light purple one on the upper right.

[Specimen #2 under "crossed filters" in two positions] Specimen # 3: The final piece to be tested is the light brown one on the bottom.

[Specimen #3 under "crossed filters" in two positions] Keeping in mind that glass is amorphous and therefore SR, quartz is DR and chalcedony is a aggregate, it is quite clear which is which. (If you don'tsee that, it would be time to re-study this section of the web lecture-> if that doesn't clear things up, it's time to email me for help!).

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[Clockwise, from upper left: quartz, glass, chalcedony] Food for thought: In the scenarios below, you have a gem reference book which lists the optic character of gems and a polariscope. You have no other testing equipment. Question 6: You have three transparent, red pieces of gem rough, (again, no labels): one is a ruby, one a garnet and one is glass. Can you find the ruby? Can you separate the garnet from the glass with your polariscope? Question 7: You are looking at two faceted, colorless stones that show visible dispersion and great brilliance. One is a diamond and one is a zircon. Can you separate them with your polariscope? Question 8: Two translucent white stones look very similar, one is a milky type of chalcedony, and the other is a white moonstone. Can a polariscope test be used to separate them? If so, what would each gem's reaction be? Testing Refractive Index The refractive index (RI) of a gem is one of the most important characteristics determining its appearance, and is also a very useful piece of data for purposes of determining the species of an unidentified gem. Without Equipment: Using no equipment it is sometimes possible to determine an approximate range for the RI of a polished gem. This is because RI generally correlates physically with the density of a gem, and visually with its luster, brilliance and dispersion. So, if I find a gem which is heavy for its size, has a higher than vitreous luster, is extremely brilliant and shows dispersion, I can just about conclude that its RI will be found in the upper ranges for gems. On the other hand, a notably lightweight piece with sub-vitreous luster, little brilliance and no dispersion, is probably to be found near the lower end of the RI range. I say it is sometimes possible, 114

though, because the degree of polish or lack of it, the number and types of inclusions, and the color or condition of the gem may make even a ballpark estimate difficult without some kind of equipment. Using Liquids of Known RI: You will recall from Lesson 3 how it is possible using liquids of known specific gravity to work out an approximate SG for a gem by immersing it and observing the reaction. There is a similar technique that can be used for RI. This technique called "Relative Refraction" uses liquids whose RIs are known. When a transparent gem is immersed in a (colorless) liquid, how clearly we can see details of the gem depends on the RI of the gem compared to the RI of the liquid. A critical concept here is "relief"; we say that a gem has high relief when it stands out as sharply visible in the liquid, and low relief when it doesn't. The greater the RI of the gem abovethat of the liquid in which it is immersed, the greater its relief. 1) A gem that is immersed in a liquid whose RI is well below its own shows high relief, the gem and its details are clearly visible 2) A gem that is immersed in a liquid whose RI is moderately to slightly below its own shows moderate to slight relief, the interior details and outline of the gem are harder to see. 3) A gem that is immersed in a liquid whose RI is the same as or higher than its own shows no relief, no edge, or interior detail is visible. The gem, if colored, looks simply like a hazy colored area in the liquid, and if it is colorless, it virtually seems to disappear! Using this basic idea we can compare the relief of two different gems in the same liquid, or we can test the same gem in different liquids. Each technique would give us information about the relative refractive index of the test pieces. Three common liquids used in this sort of testing are: water (RI = 1.33), a commercial compound called "Refractol" (RI = 1.56) and methylene iodide (RI = 1.74).

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[Liquid sold commericially for relative refraction testing: RI = 1.56] Before proceeding any further, let's see a demonstration: below is a bottle of "Refractol" and the gem petalite. The RI of petalite is between (1.50 - 1.51). Watch what happens:

[Going, going, gone!] Notice the reflections and detail visible when the gem is in air, compared to when it is immersed in the liquid. In the Refractol, it seems to disappear. You can tell that there is something in the jaws of the tweezers, but you can't make out any detail. This happened because the RI of the gem (1.50 - 1.51) was below that of the liquid (1.56). If I had not already known that the gem was petalite, but instead, was trying to identify an unknown, this test would have eliminated a great many possibilities. **Check the text: Look in the back of the Hall text and verify that diamond, white sapphire, and white topaz would all have been eliminated as possibilities by these results, but that we'd need to do additional tests to rule out quartz. Food for thought: Question 9: You have a colorless gem which you are told is phenakite (RI = 1.66). You have water, Refractol, and methylene iodide. You immerse the gem in each and get these results: in water: very high relief, in Refractol: moderate 116

relief, in methylene iodide: the piece disappears. Can you estimate the RI of this gem? Is it consistent with phenakite? Do these results prove it to be phenakite? Are there different possible results which would disprove it being phenakite? Another reason why gems are sometimes immersed in such liquids is that by diminishing the relief and reflections, internal characteristics like color zoning, fractures and inclusions sometimes stand out more clearly. If you ever go to a store or show where gem rough is sold, you can see potential purchasers dipping the rough into water the dealer has provided to get a better interior view (or less appealingly, licking the piece when no water is available!) Using a refractometer to test RI: The most commonly used type of refractometer can measure the RI of gems whose values fall between 1.30 and 1.80. This does not cover the full range of gems, whose values range between 1.20 and 2.60. When no reading can be obtained (almost always because the RI of the gem is above 1.80, the reading is said to be "OTL", or over the limits), which, in itself, is often useful information for identification purposes.

[Standard refractometer] This is a delicate and expensive piece of equipment which has numerous limitations, and is difficult to learn to use properly, yet it remains the single most useful tool for the gemologist doing gem identifications. Most models, like the one seen above, require a separate light source. The most important part of the device is a leaded glass "hemicylinder", seen as the slightly yellowish rectangle above, upon which the gem whose RI is to be read, is placed. A drop of very high RI "contact" fluid (methylene iodide saturated 117

with dissolved sulfur, plus 18% tetraiodoethylene), is placed on the hemicylinder to assure that there is no air between it and the gem. A system of internal mirrors reflects light which has been bent to a specific degree by the gem, so that it falls, as a shadow, upon a scale visible to the observer. All of this is based on firmly established principles of mathematics and optics that needn't concern us here (You can decode this as: "that your instructor doesn't completely understand"). RI Readings: • •

• • •

Can be taken on transparent, translucent or opaque gems. Are best obtained from a flat polished surface such as: o those on faceted gems
this includes some which are set in jewelry as long as the mounting doesn't prevent contact o gem rough with at least one polished face o flat polished areas of carvings or ornamental items. Can be estimated within a range for polished curved surfaces like those on cabochons or carvings. Are most accurate when a monochromatic (one wavelength only) source of light is used. Are taken with the gem in eight different postions.

[A refractometer that is ready to take a reading] In the picture above, a light source is in position, the recently cleaned gem is table down on the hemicyclinder with a drop of contact fluid in place. The 118

picture below shows what a such a reading might look like. The reading, shown is between 1.56 and 1.57. With practice it is possible to be quite accurate at estimating that third decimal place.

[Refractometer reading: Image courtesy of www.prettyrock.com] Due to the differential refraction of the various colors within white light, readings obtained with white light (as seen above) are somewhat fuzzy. Using a single wavelength source (usually yellow), produces much sharper shadows. An SR gem will give the same RI reading in all eight positions as it has no birefringence, but a DR gem will give different RIs in different directions. By subtracting the lowest from the highest, the gem's BR can be calculated. Check the text: In the texts, you can see additional pictures of refractomers in Hall on page 21, and in Lyman's book on page 47. There are also good graphics of the different appearances of DR and SR refractometer readings: (Hall, page 21; Lyman, page 49). Food for thought: Question 10: You have a group of colorless faceted gems, including: rock crystal quartz, white zircon, phenakite, white sapphire, diamond and white topaz. You'd like to find the diamond. They are not the same size or shape. You also have a gem reference book and a refractometer (and have been trained in how to use it). Which gems can be eliminated by learning their RI readings? Which ones cannot be eliminated that way? Using any test from this, or any earlier lesson, tell me how you'd find the diamond. Fluorescence

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You may recall from the topic of selective absorption, that gems may absorb parts of the visible light spectrum and convert them to heat. It is also the case that gems (due to the specifics of their chemical makeup or crystal lattices) may absorb other types of electromagnetic radiation (UV, Xrays) and convert them tovisible light. This phenomenon is known as photoluminesence. UV, or ultraviolet radiation is that part of the electromagnetic spectrum that has wavelengths just shorter than those of visible light. We divide the UV spectrum into two parts: longwave starting at 365 nm (LW), and shortwave starting at 254 nm (SW). Remembering that wavelength and energy content have an inverse relationship, this tells us that SW is the more energetic type. Although there are several expressions of the photoluminescence phenomenon that can be tested for in big gem labs, the type which is most useful to the average gemologist is fluorescence testing. Fluorescence: When a gem absorbs either SW or LW UV, or both, and immediately emits visible light, the phenomenon is called fluorescence. In order to test for fluorescence it is necessary to have a controlled source of SW and/or LW and a darkened viewing chamber. (It is also prudent to have UV protective eyewear as exposure to these rays can be damaging.) The specifics of the color and intensity of fluorescence can sometimes be a useful diagnostic test in identifying gems. A typical UV test lamp, as seen below, usually consists of a light source which produces the UV with a pair of filters covering it. On one side a filter blocks SW and permits LW to pass, and on the other end LW is blocked passing the SW. In the model below, a simple metal slider mechanism is moved from one side to the other to block out the undesired wavelengths. The test would be performed inside a viewing chamber that blocks out all visible light. The gem to be tested must be very clean as skin oil and dust particles often fluoresce brightly.

[Fluoresence tester: set up to test with SW, set up to test with LW] 120

Fluoresence can be absent, in which case we say the gem is inert, or present in weak, moderate or strong form. The light emitted by fluorescence can be the same color or a different one from the color of the gem itself, and a gem can have the same or different reactions to LW and SW. •

• •

Natural, white to light yellow diamonds often fluoresce blue--> about 30% of them do so. This can be a benefit or a liability in terms of value. In some cases the fluoresence (which happens to a slight degree even in daylight--(why?) can make a yellowish stone look "whiter". In other cases, the effect, if strong enough, can produce a kind of fuzzy or greasy look in the diamond and degrade its appearance. Most often, however, it has no noticeable effect at all. (There have been incidents where customers have been surprised or even angry at their jewelers when they've worn a diamond necklace or bracelet into, say a nightclub or other situation where "blacklights" we used, and found that some or all of their diamonds "lit up".) Fluoresence, then, is one of the aspects important to consider when replacing a lost diamond in a cluster setting, and trying to match color. Natural emerald is usually inert, whereas some of the most common types of synthetically produced emeralds fluoresce red. Natural Burmese and some Vietnamese rubies fluoresce red (even in sunlight). They do so because of the same chromium oxide that gives them their color. Rubies from other locales (Sri Lanka, Africa, most areas of Thailand) also are colored by chromium oxide, but they generally alsohave some iron oxide in their chemical makeup which "dampens" or prevents the fluorescence. The outcome of this is that a good quality ruby from a Burmese source has a special kind of glowing red color seen in no other gem, and it is the basis for their higher value compared to other rubies. Synthetic rubies often show this effect even more strongly than Burmese stones.

[Burmese ruby ring in visible light, fluorescing red under UV (no visible light is present)] 121

Fluorescence testing is usually, at best, supplemental, it is rarely defintive. There is one notable case, however, where the test can provide proof of identity: Benitoite. There is no other blue gemstone which shares its distinctive reaction of being inert to LW, and fluorescing a strong, chalky blue with SW.

[Benitoite under: visible light, LW UV, SW UV] Check the web: This page has a cool "mouse over" feature that reveals the appearance of a number of mineral species under UV:http://mineral.galleries.com/minerals/fluoresc.htm Testing the Absorption Spectrum of a Gem A "spectroscope" contains a prism (or a diffraction grating) which serves to disperse incoming light. This light, which has been reflected or transmitted from the gem being tested, enters the spectroscope, and is dispersed to display as a rainbow spectrum through the eyepiece. If significant selective absorption has taken place, then certain portions of that spectrum will be "missing" or reduced. Black or darkened lines or bands indicate which wavelengths have been absorbed by the gem and to what degree. The lines can be very distinct and quite sharp indicating that the gem has absorbed very strongly in a small region of the spectrum, or broad and indistinct indicating a more general absorption over a wider band of wavelengths. Hand held models are relatively inexpensive, but difficult to learn to use effectively, and to provide adequate lighting for. Desk models are very much more expensive (the one from GIA, pictured below, is $5000) but easier to use, and more accurate. The spectroscope is used with a handbook of printed gem spectra for comparison. Big labs have high tech versions, using specialized lighting (or other energy sources, like infrared or Xray), special cooling (liquid nitrogen), etc.

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[Procedure for using a handheld spectroscope: Image courtesy of www.prettyrock.com]

[GIA "Prism 1000"model spectroscope: Image courtesy of GIA Gem Instruments] By comparing the two spectra below, it is easy to see how distinctive an absorption spectrum can be. In such cases the spectrum may be diagnostic of species, coloring agent or even location of origin. Less than 25% of gem species, however, show clear, unambiguous, absorption spectra like these. The percentage of gemologists who can accurately use a pocket spectroscope is probably even smaller than that! (And I cannot be counted among them.)Usually, therefore, spectroscopic examination is a supplemental, rather than a diagnostic, test.

[zircon spectrum: Image courtesy of www.yourgemologist.com] [almandite garnet spectrum: Image courtesy of www.yourgemologist.com] Answers to the thought exercises for this lesson. (If you don't understand why these are the correct answers, then it's a good time to email me and ask!)

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1) They mark the optic axis direction so that the cutter can be sure to orient the table of the stone in the proper direction. When a Moissanite is cut with the table in the optic axis direction, its birefringence isn't noticeable, and it looks more like a diamond. 2) The table view looks as if the stone is SR. When you tilt the stone you are looking through it in a non-optic axis direction, and in this case you see doubled facets indicating that has birefringence and therefore is DR. Since diamond is SR, and the stone is DR, it cannot be a diamond. Moissanite, used as a diamond simulant is DR, so the gem could be a Moissanite. Another possibility would be a white zircon, a natural stone used as a diamond simulant which is also DR. 3) Yes, by testing the three gems with the dichroscope you would find the one which shows no pleochroism which would be the spinel which is SR. The other two would have pleochroism. You could compare the other two to separate them: iolite is trichoic so you'd see three colors, sapphire is dichroic showing only two. 4) Yes, the ruby would be the one that was dichroic. The other two, being SR gems wouldn't show pleochroism. No, using just the dichroscope and no other test or information you could not separate the garnet and the glass. (testing for RI or specific gravity would easily separate them, though.) 5) Because non-crystalline (amorphous gems) like opal, amber and glass are SR. 6) Yes, the ruby would be the only one which would give a DR reaction in the polariscope test. No, (as with the dichroscope in question # 4) both the garnet and the glass would give SR reactions. 7) Yes, the diamond would test SR and the zircon would test DR. 8) Yes, chalcedony (as an aggregate) gives an AGG reaction (always light) to the polariscope test, while moonstone (being a crystalline gem of the monoclinic system) tests DR (blinks light and dark when turned). 9) Since the gem shows no relief (disappears) in methylene iodide whose RI is 1.74, the gem has a lower RI value than that. Since it does show relief in Refractol whose RI is 1.56 you know that it has an RI higher than that. So its RI lies between 1.56 and 1.74. Since phenakite's RI is 1.66, the gem could be phenakite. These results do not prove it is phenakite, however, as there are 124

other colorless gems with RI's between 1.56 and 1.74, like Danburite, for one. Other results that could have disproven an identity of phenakite would have been: if the gem disappeared in Refractol (its RI would be below 1.56) or if it showed relief in methylene iodide (its RI would be above 1.74). Such results would be incompatible with phenakite. 10) All the listed gems (except diamond and zircon) have RI's below 1.80 and so could be ruled out as being diamond which has an "OTL" reading on the refractometer. So you'd be left with the diamond and the zircon. There are many correct ways to answer how can these two be separated but two of the ways would be 1) Specific Gravity (zircon is much heavier than diamond), since they aren't the same size and shape you couldn't do it by hefting or comparing measurements, but you could do it by hydrostatic weighing and 2) Optic Character (diamond is SR, zircon DR) you could do a polariscope test or check with a loupe for doubled facets to find the zircon. You have now completed the web lecture for the fourth lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Five: Magnification and What it Reveals

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MAGNIFICATION AND WHAT IT REVEALS A reasonable question which might be asked is, "Why magnify a gemstone"? After all, we don't go around with magnifiers looking at our gems and jewelry, we just view them with the naked eye. There are several very good reasons, though, why it's desirable and in some cases, necessary, to get an interior view: 1) Appraisal/insurance/repair: When you take gems or jewelry items to get them officially evaluated, perhaps due to an inheritance or insurance issue, or for investment reasons, there must be a way for the appraiser to both justify their analysis of the gem, and to document that particular stone, so that its identity can be verified in the future. In order to assign a value to any gem, it must be graded, that is, a determination must be made as to how fine, and how rare it is, and what its "market" or "replacement" value would be. Part of the grading process which determines these values, especially in diamonds, is done under magnification. The magnified view of any gem, plotted onto a diagram, can then serve as its "fingerprint". It is about as unlikely that two gems will have the same number, location, and type of inclusions and internal growth features, as it is that two people will have the same fingerprints, or the same DNA. Such a drawing will also give the jeweler who is receiving a valuable jewelry item for cleaning or repair, and the customer, a way to verify that the gem taken in is, in fact, the same one which is returned. 2) Gem Identification/Gem History: In general, the three questions a gemologist or appraiser (or a savvy buyer!) has to ask about an unknown gem are: What is it? Although this question can usually be answered by tests of those physical and optical properties discussed in Lessons 3 and 4, finding certain inclusions can make the job easier, and in some cases eliminate the need for further tests. In addition, some optical and physical properties are best revealed under magnification.

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[The characteristic growth tubes inside this gem narrow the most likely identification possibilites to beryl and tourmaline (it's a tourmaline)]

[The doubled facet reflections seen under magnification in this sphene and zircon, serve as clues to gem identity: few species have birefringence this high] Is it natural or synthetic? Once the question of the species or variety has been answered, then it is necessary to know whether the gem is natural or synthetic. (Remember, synthetics are the gem, and, therefore, have all the chemical, physical and optical properties of the natural version). One of the best tools at a gemologist's disposal, in trying to make this call, is magnification. There are certain inclusions found only in natural stones, and others found only in synthetics. In many cases, then, seeing a certain inclusion is definitive. Unfortunately, there are also inclusions which can be found in either type, and some gems that are so totally clean, there are no inclusions to use.

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[The triangular platinum crystals which were eroded from the crucible in which this synthetic Alexandrite was formed, give proof of its man-made origin] Has it been enhanced, and if so, how? Certain enhancements (and imitations) can be most easily detected by a magnified view of the surface, or the interior, of a gem.

[The intact "silk" (rutile needles) in this sapphire proves that it has not been subjected to high heat, and is of natural color, whereas the stress fractures in this heated sapphire give evidence of its treated state: Image courtesy of Martin Fuller] Where, specifically, did it come from? Though not a factor in most cases, there are a few important instances where the geographic location of a gem's origin is crucial in setting its value. In those situations, it is often possible by seeing diagnostic inclusions or growth features to specify the location. Only peridot from Arizona shows a characteristic stress fracture/included crystal combination known as a "lily pad", and only demantoid garnet from Russia, shows microscopic curving fibers of bryssolite asbestos known as a "horsetail".

[Lily pads in Arizona peridot, a horsetail inclusion in Russian demantoid garnet] 128

Check the web: This URL takes you to a news bulletin of the Gemmological Association of Australia, documenting the characteristic inclusions of rubies from a new source in Madagascar: http://www.gem.org.au/rubynews.htm 3) You can see very cool things! Looking into a gem can reveal a world of beauty and complexity that just isn't apparent from a surface view. Tools: The two tools most often employed in gemstone magnification are the loupe and the gem microscope. The loupe: A loupe is a small magnifying device, which, most commonly, magnifies the object to be viewed to ten times its size (10x). There are five major types used by those observing gems: handheld, eye socket, headpiece, eyeglass, and darkfield. Each has its advantages and particular best use. The handheld version is the most versatile, and the darkfield type supplies a source of specialized lighting important in some aspects of gem identification and/or grading. The eyesocket, headpiece and eyeglass types have the advantage in situations where leaving the hands free is important.

[Loupes: handheld, eye socket, headpiece, eyeglass (images courtesy of www.riogrande.com), darkfield]

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In general, the advantage of a loupe over a microscope is its portability and low cost. On the other hand, the loupe's capabilities of magnification and lighting are limited compared to most microscopes. A Warning! Some of you probably already own a loupe or have taken the advice from the course syllabus and recently acquired one. So, before we get any further into the technical aspects of magnifying tools and techniques, let me give a warning: Use this tool with caution--> the view can be scary sometimes! The first time a new loupe-user looks at their favorite piece of gemstone jewelry at 10x, they are in for for a rude awakening. A piece of gemstone jewelry which has been worn to any extent (and which looks perfectly fine to the naked eye) shows, to the examiner with a loupe, scratches and gouges in the metal, and glaring manufacturing flaws like incomplete solder joints. Upon turning his/her attention to the gem, what meets the eye is globs of dirt and grime surrounding the gem, and in most cases startlingly visible "crud" insidethe gem, and/or worrisome chips, scratches or fractures on its surface. By way of demonstration, let's look at a couple of perfectly lovely gemstones: a (rather expensive) Tsavorite garnet, and a modestly priced bicolored tourmaline cabochon.

The Tsavorite gem has no visible problems and looks great, completely transparent and full of sparkle and color. The tourmaline, as is the case with most cabochon gems, is of lower quality than a piece that would have been faceted, and is translucent, but still very attractive. The view using our loupe, is somewhat different:

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OK, now that I've properly warned you, let's look on the bright side and view some of the "very cool" things mentioned above: Just for fun! Here's a nice dendritic chalcedony which at 10x really shows the three dimensional nature of the dendrites and gives some insight into their growth pattern as well.

Two interesting drusy gems, but at 10x we can actually tell that their surfaces are lined with real crystals (albeit small).

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[Drusy quartz and drusy vanadinite]

[Rutilated quartz, same stone at 10x] The pair of pictures below is of the same inclusion within a gem--> the gem has been tilted about 30 degrees in the second shot. What you are seeing is the movement of a gas bubble within a pool of liquid within a cavity in the gem. The first time you look inside a rock and see something moving it's quite a thrill! Such a moveable bubble is referred to as an "enhydro" and is much sought after by collectors.

[An "enhydro" inclusion in quartz]

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Check the web: This website gives a visual demonstration of how interesting and different ordinary things can look when they are magnified:http://www.theimage.com/closeup/ The Hand Loupe: Triplet Loupes: The highest quality (and most expensive) loupes actually consist of a set of three glass lenses fitted together, and are referred to as "triplets". Together, the set of lenses corrects for the inevitable distortion introduced when a single lens is used. This distortion is of two types: chromatic and spherical, and both types are caused by the curved shape of the lens, particularly at the edges where the curvature is the greatest. In chromatic distortion, the unequal bending of the different color wavelengths creates dispersive color fringes at the edges of view. In spherical distortion, a similar mechanism causes the image itself to curve and be out of focus in those areas. Single lens loupes are available at very low cost, and are just fine for nonprofessional applications. If your loupe is not a triplet type, no need to worry--> all you need to do to compensate, is to confine your observations to the central area under view, and things will be fine. Hand loupes can be found from 2x to 30x magnification. It might seem a good choice to purchase the one with the highest power, but typically that isnot the case. There are three reasons: 1) The higher the power of magnification, the shorter the "focal length" --> the distance from the lens to the object so that it is in focus. For a 10x lens that distance is one inch, (20x = 1/2 inch, and 30x = 1/3 inch). It is difficult enough to work with a 1" clearance, let alone any of those shorter distances! 2) The shorter the focal length (higher power) the less light can enter the gem. Again, getting proper lighting at a distance of 1" can be a challenge, but it is very much more difficult at the shorter distances available at higher magnifications. 3) The higher the power of magnification, the smaller the "focal area" --> the size of the patch that you are magnifying. It can take quite a while to throughly examine all areas of a gem while using 10x, the job becomes harder, the smaller the "patches" you are looking at.

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It should not be surprising then, that the vast majority of loupes in use are 10x. Most loupes come with a metal cover that doubles as a "finger hold" or handle. The correct technique for using a loupe is pictured and described below:

1) Put the index finger of your non-preferred hand (left hand for righties, and vice versa) through the loupe cover and bring the loupe to rest against your thumb which is resting on your cheekbone. (This gives you just about the right eye-to-loupe distance. 2) In your other hand are your tweezers with the stone (either a girdle to girdle, or a table to culet hold is fine). The tips of the tweezers are between your middle and fourth finger. This allows you to easily and stably pivot the stone forward and back (with the hand holding the tweezers) to adjust the focal length to the 1" required. 3) Once you have mastered the basic "hold" you can actually focus on different "depths" within the gem by slightly increasing or decreasing the gem's distance from the loupe. First bringing the surface into focus, for example, then moving the focal area into the interior and finally to the bottom of the gem. 4) Unless you have severe astigmatism you do not need to wear your glasses.

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5) Keep both eyes open. If you haven't used magnifying devices before, this takes some discipline to do, as your natural inclination is to close one eye. You can view comfortably for a much longer period of time with the "two eye" technique, and as a bonus, you usually don't end up with a headache. The Darkfield Loupe: The ideal lighting condition for revealing inclusions in a gem is known as: "darkfield illumination". In this situation the gem is viewed against a black background with the light coming through it only from the side. The effect is to make any interior features stand out sharply in relief, and to be much more noticeable than with ordinary lighting. Although gem microscopes provide this lighting choice, most loupes do not. The exception is a device known as a darkfield loupe. The housing into which the gem is placed for viewing has a central, black baffle which prevents light from the source (usually a small "maglite" type of flashlight) from shining straight into the gem. Instead the light is reflected from the shiny sides of the housing to enter the gem sideways.

The technique for using a darkfield loupe, couldn't be simpler: the gem, in its tweezers, is simply rested in the opening and viewed at a comfortable distance. These are much more expensive than hand loupes, but for those who need to grade gem clarity on a regular basis, are well worth it. Gem Microscope: A gem microscope is similar to a biological or medical microscope in that it is binocular, and uses compound lenses. A binocular magnifying device has two eyepieces so that both eyes are used at once. This is ideal for getting a good three dimensional view. In a compound scope, there is a set of lenses 135

close to the object being magnified (objective lenses) and a set in the eyepieces (ocular lenses). With this set-up, magnification is compounded, meaning that, for example, if the objective lens is 5x and the ocular lens is 10x, the total magnification is 50x. Gem scopes differ from biological scopes in that the total maximum magnification is usually lower (about 70x as compared to as much as 1000x) and there are more lighting options. For example, a good gem microscope has: brightfield illumination, darkfield illumination, oblique lighting, overhead lighting, a light diffusing system, a system for immersing the object in liquid in a well for viewing, and a light polarizing set up. They also generally come fitted with a pivoting stone holder.

[ A typical gemological microscope, both eyes open is best] In the diagrams of the under stage areas of the microscopes below, you can see a comparison of brightfield and darkfield illumination. With brightfield lighting the light entering the gem comes from below as well as from the side. The amount of light entering the viewing area is manually controlled by an iris diaphragm, and frequently diffused with a special frosted glass coverplate. This type of lighting is ideal for seeing color zoning, dye concentrations, and the curved growth bands indicative of certain types of synthetic gems.

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When the moveable baffle plate is put into place, darkfield illumination is produced which enters the gem only from the side. The highlighted internal features are then viewed against the black background of the baffle, and stand out in high relief. This sort of lighting is best for examining and identifying inclusions in a gem.

**Check the text: On page 52 of the Lyman text, is a good analogy of what you are seeing via darkfield. Also important is overhead lighting (sometimes called reflected or incident lighting). In this case the light source in the well of the microscope is turned off, and an overhead light used instead. Such illumination is excellent for 137

examining the surface of the gem for blemishes, and for details of the finish, such as polish and facet meets. Compare the two pictures below taken of the same gem (at 10x magnification) under reflected light and darkfield. Notice how the surface features are so much more noticeable in the first instance, and the internal features better displayed in the second.

Food for thought: (Answers will be found at the end of the lesson) Question 1: You have been given a gem to examine microscopically. Which type of lighting would be best suited to determine each of the following: The likelihood that it is synthetic or enhanced with dye? The fine points of its cut and polish, and the degree of wear and tear it has sustained? Its clarity? What Can Be Seen? The clarity characteristics of a gemstone are divided into those that are seen on the surface (blemishes) and those in the interior (inclusions). Blemishes and other surface features: In this category are chips, scratches, knicks and abrasions, as well as attributes of the faceting or lapidary process such as degree of polish, or shape and placement of facets. A survey of the outside of the gem can yield several important results. 138

1) Gems are graded for color, clarity and cut. Some of the surface features are used in setting the gem's clarity and/or cut grades. Surface features, in general, affect the clarity grade less than do inclusions, but there are some important exceptions. A surface-reaching fracture, for example, is considered a blemish, but it greatly diminishes a gem's clarity grade because it decreases durability. 2) The surface view can yield important gem identification information. Examples would be abraded facet junctions which give hardness clues, or characteristic surface features like the "engine-turned" effect that is diagnostic for elephantine ivories. 3) Telltale signs of imitation gems or gem enhancement are often observable on a gem's surface. This would include concave facets or mold marks as seen on glass and plastic, and dye concentrations in surface reaching fractures. Below are some examples of important surface features:

[An unpolished area of a diamond girdle (a "natural") showing "trigons": triangular growth marks that prove diamond identity: image courtesy of Joe Mirsky, the "engine-turned" effect proving natural, specifically elephantine, ivory, a surface reaching fracture in a sapphire which substantially lowers its clarity grade: image courtesy of Martin Fuller] Inclusions and other internal features: Internal clarity characteristics of a gemstone are represented by four major groups: solids, cavities, cracks and growth phenomena. 1) Solids: Solid material seen inside a gem is usually some type of included crystal. Crystals can be large or small, they can have an RI similar to, or quite different from, their host, and they can be many different species, including the same species as the host. 139

Not only are the crystals likely to affect the clarity grade of the gem, they also can be suggestive or diagnostic of its species, enhancement status, or location of origin. Included crystals with rounded, rather than sharp edges, can be indicative of high temperature heating for example which might occur naturally or during certain types of treatments. The majority of crystals are either formed at the same time as the gem, from other minerals present in the melt, vapors or fluids, or pre-existing ones which the growing gem captures. Less frequently, the crystals appear after the gem is first formed. A noteworthy process, in this regard, is "exsolution". It occurs after the initial formation of the gem, and involves re-crystalization of materials which may, initially, have been dissolved in the gem. As you will recall from Lesson 3, gems may have several stable points of temperature and pressure at which they can crystallize. Picture a gem forming at one set of conditions and then later being partially, or wholly, remelted and subjected to new conditions. Rutile, for example, can be dissolved in corundum, or exsolved. When it exsolves it crystallizes as discrete needles. This phenomenon is used by gem treaters to add or subtract rutile needles from sapphire at will, respectively ehancing the potential star in a gem, or clarifying a cloudy one. Another "after the fact" way in which crystals get into a gem is by invasion of cracks by fluids. This is the mechanism by which the dendrites in chalcedony form, as well as that which is responsible for the seams of precious opal in a matrix rock.

[Spinel crystals in spinel, diamond crystal in diamond]

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[Goethite "sheaf" in citrine, cubic and prismatic crystals in beryl]

[Fibrous hematite cyrstals in strawberry quartz] 2) Cavities: Voids within a gem can contain liquid, gas (bubbles) or solids, and as remnants of the gem formation process, are quite often important in determining identity or the location of origin. Since bubbles are extremely rare in natural crystalline gems, they are very good indicators of either amorphous gems like glass, or synthetics. Bubbles usually can be distinguished by their rounded or oblong shapes, and their very high relief. In cases of doubt as to whether something is a bubble or a rounded off crystal, polarized light can generally be used to discriminate.

[Bubbles in Moldavite (a natural glass), and in cubic zirconia (a synthetic)] Food for thought:

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Question 2: Why would bubbles have particularly high relief, and why would they generally be distinguishable from rounded crystals by using polarized light? Cavities with both a liquid and a gas trapped inside are called "two phase" inclusions, and those that also contain a solid crystal are termed "three phase"inclusions. In the vast majority of cases, two and three phase inclusions are indicative of natural origin.

[Classic three phase inclusions in emeralds from Chivor, Colombia: images courtesy of www.gemtec.com, two phase inclusion in emerald: image courtesy of Martin Fuller] 3) Cracks: It's time to learn a new euphemism! Cracks, which can be either fractures or cleavages, are, in the gem world, given the disarmingly attractive name of "feathers". It does sound nicer, doesn't it, to say that your gem has several feathers, rather than using harsher (but more realistic) language? Feathers can occur during the formation of a gemstone, perhaps as a result of rapid heating or cooling, or through pressure or mechanical stress. They can also occur long after the formation process, for the same reasons. They can be entirely within the gem or can reach the surface. Under some conditions such a break within a gem can act as a diffraction grating and create a small dispersive rainbow of color, known as a "cleavage rainbow".

[Cleavage rainbows in a quartz specimen, and a piece of diamond rough, with an internal fracture] 142

Surface-reaching fractures not only impair durability, they also are portals for fluids to enter which may cause stains or, in the case of enhancement, accept and concentrate dyes.

[A non-surface reaching feather within a tourmaline, a surface reaching crack in a sapphire showing natural staining material]

[The fractures in these Indonesian chalcedonies have allowed iron staining to create fortuitously meaningful patterns] Feathers that exist within a still-forming gem, can be partially healed by penetration of growth fluids, or later by partial remelting of the material. Such partially healed cracks often show up under magnification as a series of tiny dots in rows or arcs. They look quite a bit like their namesake: "fingerprints".

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[A natural ruby containing multiple fingerprints, closeups of fingerprints in Kunzite and in Tsavorite garnet] This healing process, in essence, acts like a set of tiny "spot welds" which hold the sides together, and prevent the crack from enlarging. For this reason, the presence of fingerprints in a gem does not negatively affect its durability, and usually, unless there are so many of them that they impede light, have little effect on the gem's transparency. Most knowledgeable observers are happy to see at least a small fingerprint in a gem, as it is very strong evidence that a gem is natural rather than synthetic! There are some inclusions in synthetic gems which superficially look like fingerprints, but close examination by a trained eye can usually identify them not as fingerprints, but as remnants of the solid fluxes used in the synthesizing process. Several gem ehancement processes exist whereby surface reaching feathers in a gem can be "filled" with oils, resins or glass. The goal here is to disquise the crack by replacing the air in it with something closer to the gem's RI, thereby reducing its relief. This is a standard practice for emeralds, and occasionally seen in rubies and diamonds. Similar techiques are in use to fill the cracks caused by "crazing" in opals. In diamonds, lasers have been used to tunnel inside to reach internal feathers and treat them.

[Oil-filled fractures in emerald, image courtesy of Martin Fuller] 4) Growth Phenomena: This "catch-all" category includes visible evidence of twinning, and other features of the gem's growth . Examples include "swirl marks" which occur in amorphous materials, primarily glasses, and either curved or straight growth or color zoning patterns which may help distinguish natural from synthetic gems. In single crystal gems, curved growth lines (striae) or color patterns always mean synthetic, whereas straight ones can be found in either natural or synthetic gems. Growth and color zones are best observed with diffused light or under immersion in a liquid. 144

[Definitive: swirl marks in Moldavite, indicating glass, and curved growth striae proving the synthetic origin of this ruby]

[Inconclusive: straight growth zoning in synthetic flux grown ruby, straight color zoning in natural sapphire.] The columnar or "chickenwire" pattern of color blocks in opal is a sure sign of a man-made product.

[Chicken-wire and columnar opal color blocks proving man-made opal] **Check the text: Pages 52-53 in Lyman and 24 and 25 in Hall, have some nice pictures of inclusions and growth features. Clarity Grading of Gems: Nature's reality is that the clarity of gems runs as a continuum from completely flawless to extremely highly included. Humans, though, always like to make boundaries and put things into discrete categories, and so it is with clarity grading of gems. Grading systems, especially for colored stones vary widely in the exact terminology they use, but all such systems describe at least four major categories of clarity:

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1) Flawless: No inclusions can be seen, even at 10x magnification. Very few gems are in this category as the geological and biological processes which create gems usually leave some visible evidence. Some types of laboratory synthesis processes routinely produce flawless stones, while others yield gems with inclusions. (Flawless natural-origin gems come at a premium price, and it would be prudent for anyone contemplating a high value purchase of a gem without inclusions, to have the gem certified as natural by a gemological laboratory, as there will be no visible internal evidence as to origin.) 2) Eyeclean: In this category, gems, as seen under the normal viewing conditions: face up, in normal lighting, and about 12-14 inches from the viewer, look clean. Increasing the light or turning the gem on its side or bottom (which cuts down on reflections) may reveal visible inclusions, though. When viewed at 10x, gems in this category range from having few and hard to find inclusions, to having large, rather obvious ones. To many, this is the ideal condition for a gem--> the reason being that there are internal signs of its natural origin, yet it still looks great. 3) Slightly Included: Gems given this description, or some variant of it, have eye visible inclusions or blemishes, but they do not notably spoil the beauty of the gem, nor markedly degrade its durability. Some types of gem materials are rarely found with greater clarity than this: examples would be emeralds and many red and pink tourmalines. Often gems with visible inclusions are good bargains as they can still look very nice, but are usually available for lower per carat prices than those of higher clarity. 4) Included: This category covers the gems with such overtly visible or numerous inclusions as to moderately to severely impair beauty or durability. Usually only very rare collector gems, or extremely inexpensive pieces are acceptable in this condition. Food for thought: Question 3: Why did I stipulate "certified as natural" by a laboratory in the above? These four main groupings can be subdivided into a larger number of groups by using terms and phrases like: "very slightly", "moderately", "almost", "better than", just short of", etc., to modify the main terms. So, for example, a colored gem that has few and tiny eye visible inclusions might be called "very, very, slightly included" while one that has only one or two

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barely findable inclusions under 10x might be termed "better than eyeclean" or perhaps "just short of flawless at 10x". Colored Stones -vs- Diamonds: Colored stones are frequently clarity graded with the naked eye, and to less exacting standards than are diamonds. GIA, for example, uses seven categories for colored stone grading, while with diamonds, which are clarity graded at 10x, eleven different clarity groupings are made. Within colored stones, the standards for clarity vary by species. Some types of gems occur commonly with few inclusions, while other types generally have many. Emeralds are an example of a gem that rarely, if ever, is found in clarity greater than eyeclean, while amethyst is often quite clean, even at 10x. Emerald clarity, therefore, is usually graded on a less rigorous scale than that used for amethyst. The inclusions that rate a clarity of: slightly included for an emerald, might generate a grade of "moderately included" for an amethyst. Within a species, then, the grade is set, by the overall number, position and type of inclusions. Those that affect beauty or durability will be the most important. Examples of inclusions or blemishes which have a minor impact on grade would be: a group of tiny crystals located under a bezel facet where reflections make them hard to see, a poorly polished table, or color zoning which cannot be seen face up. (In general, blemishes have slight impact on the clarity grade due to the fact that a gem can be repolished or recut to remove them). Examples of serious inclusions would be: a surface reaching fracture, especially on the girdle or crown (where the gem is subject to the greatest stresses), a "reflector inclusion" (one whose position causes light reflections to create multiple images of it) or a "stab in the heart" (an inclusion clearly visible through the table of the gem).

[A single "reflector" inclusion which appears, by reflection, to be many, in a diamond: image courtesy of Martin Fuller, a black "stab in the heart" inclusion visible through this sunstone's table.(near center, right)] An Exception to the Rules: 147

A notable exception to the way in which gems are clarity graded would be in the case of those gems whose visible inclusions create its value, rarity, or beauty. In that case, only the surrounding gem material is clarity graded. In the photos below, we see two such cases: the "trapiche" emeralds with their black "cog-wheel" inclusions are rare collectors items, and so the clarity grading would be done in regards to the green areas only, the "confetti" sunstone is desirable primarily due to its glittery hematite particles which flash gold, red and blue, so the clarity grade speaks to only other, extraneous, inclusions that might be present.

["Trapiche" emeralds, "confetti" sunstone] **Check the text: On Page 25 of the Hall text is a picture of a carved rock crystal perfume bottle labelled "Rutile Needles": I think this is an error and that these are tourmaline needles, to my knowledge rutile is never black. Regardless of which the needles are, though, this object is a good example of inclusions adding value. Answers to the thought exercises for this lesson. (If you don't understand why these are the correct answers, then it's a good time to email me and ask!) 1) a: Diffused brightfield lighting is best for this, as it can reveal color zoning and growth patterns that might indicate synthetic origin, or unusual concentrations of color that might indicate dyeing or diffusion. b: Overhead (or reflected) light would enable you to see nuances of polish and the exact number and placement of facets. Any scratches, nicks or chips on the surface would also show up clearly. c: Darkfield illumination is best for clarity observation as it displays any inner structures at the highest possible relief. 2) Bubbles are filled with gases which are less dense and therefore of much lower refractive index than gems, their relief, therefore, would be high. Most crystals (with the exception of those in the cubic system) will flash dark and light when polarized light is shone through them and a polarizing lens is turned above the image. The gases inside bubbles would not do that. 3) A flawless gem, by definition, has no inclusions or other microscopically visible internal characteristics that might help an ordinary gemologist or jewler 148

identify it as of natural origin and/or unenhanced status. The specialized equipment of large laboratories, like those of GIA, would therefore be necessary. In rare cases, there are no current tests which can absolutely rule out certain enhancements, and the best such labs can guarantee if this is true is "no signs of enhancement or synthetic origin were determined". You have now completed the web lecture for the fifth lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Six: Optical Phenomena in Gemstones

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OPTICAL PHENOMENA IN GEMSTONES I initially thought to title this lesson "Phenomenal Gems", but recalling an incident from a few years ago, I opted for the longer title. I was the evening's speaker for a local Rock and Gem Club meeting, and as I was being introduced to folks prior to the meeting, a young boy asked me what I'd be talking about. My reply "Phenomenal Gems", brought a perplexed smile to his face, and the query: "Do you mean really, really, BIG ones?" Optical phenomena encompass the light-dependent properties of a gem, which are not due to its basic chemical and crystalline structure, but rather, due to the interaction of light with certain inclusions or structural features within the gem. Major Optical Phenomena in Gemstones: •

• • •

•

Iridescence, including: o Orient o Labradoresce nce o Play of color Adularescence Aventurescence Chatoyancy, including: o Simple chatoyancy o Cat'seye effect o Asterism Color change

**Check the web: Optical phenomena are not limited to gemstones, for a neat overview of other interactions of matter with light (like rainbows and the aurora effects: borealis and australis): go to this URL:http://en.wikipedia.org/wiki/Optical_phenomenon (warning--> you could get stuck here for hours, it's so interesting!)

Iridescence: This phenomenon is seen as a multicolored, surface effect. It is caused by diffraction. As white light passes through very small openings such as pores or slits, or through thin layers of material which differ in refractive index, a prism effect causes it to separate into spectral colors. 150

These may then be seen on the surface, or in some cases in the interior, of the material. Iridescence is responsible for the everyday observations of the spectacular colors seen in the metallically shimmering neck plumage of male Mallard ducks, peacocks and some hummingbirds, or as light catches the surface of a soap bubble. When combined with interference, where the slightly out of phase color waves bouncing off different layers overlap as they reflect, a loss of some colors and a reinforcement of others can take place giving rise to dramatic color blocks, which may shift with viewing angle. Iridescence is the most widespread of the optical phenomena, we see its effects in: the "orient" of pearls, the displays of fire agate, "rainbow calcite", certain obsidians, and iris agate. It also creates the rainbow display of fractures, the beautiful colors of Labradorite, and, probably most well known, the "color play" of precious opal. Pearls: The "orient" of pearls, is a delicate, shifting, iridescent color layer that is distinct from the basic body color of the pearl or from its luster. Both luster and orient are a function of the thickness and perfection of the layer of nacre on the pearl's surface. Nacre is composed of thin plate-like layers of aragonite (CaCO3) crystals accounting for over 90% of its weight, along with conchiolin protein, and water. Although most pearls have that characteristic "pearly luster", only fine quality pearls have orient. It can also be present in the "mother of pearl" lining of shells, and is especially vivid in the shells of some species of abalone.

[Displays of orient: baroque freshwater cultured pearl, cultured Tahitian black pearl, abalone shell doublets] Fire Agate: The aggregate quartz gem known as fire agate, gets its iridescence from thin coatings of iron oxide (limonite) layered over its botryoidal chalcedony surface. The best specimens of this material can be 151

very striking, and will command some of the highest prices of any aggregate form of quartz.

[Fire agate cabochon in a pendant, a close up view of some fire agate colors] Ammolite: This gem is the result of the fossilization of extinct, shelled mollusks, called ammonites. Although many ammonite fossils are found, only a certain type from a restricted area in Canada shows the iridescent effect, which has preserved, and enhanced, the thin, tablet-like aragonite crystal layering of the shell. Although delicate, and not suitable for some jewelry uses, the gem has many admirers and top quality pieces will fetch high prices. The thickness of the preserved layers controls the colors that will be seen. Thicker layers produce red or orange colors, and thinner ones, the blues and violets. Due to the fragility of the thinnest layers, specimens with blue or violet color are especially rare and costly.

[A fine specimen with rare blue and violet colors, and one with the more commonly seen red, a 10x view of green, blue and red iridescence on an ammolite] **Check the web: For a tour of one of the World's largest ammolite mines, visit this URL:http://ammolitemine.com/mine_tour.htm Phenomenal obsidian: Most obsidian is pretty plain looking, in mostly drab shades of brown and black. Certain types, however, display iridescent patterns due to dense congregations of minute suspended inclusions that act

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like diffraction gratings. Fanciful trade names like "velvet" or "rainbow" obsidian are used to market these lovely gems.

[Rainbow obsidian cab, rainbow obsidian cut as a "cat'seye", velvet obsidian] Fractures/Cleavages: As noted in the lesson on magnification, an internal cleavage can give evidence of its presence by a "cleavage rainbow". The picture below, showing impressive iridescence, is a magnified view of a very thin conchoical fracture in a gem.

[Conchoidal fracture in aquamarine: Image courtesy of GIA] There are other cases, where rather than revealing a defect, the presence of microscopic fractures or cleavages is responsible for the beauty of a particular gem. Two examples which are admired by collectors are known as "rainbow calcite" and "iris quartz".

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[Iridescence due to internal micro-cleavages: "rainbow calcite";"iris quartz": Image courtesy of GIA] Labradorescence: This phenomenon is a type of iridescence caused by repeated, microscopically thin layer (lamellar) twinning in Labradorite feldspar. One of its most notable characteristics is that the twinning is quite specifically oriented within the crystal, making the iridescent display highly directional. (Another is that it is seen in only this one species.) At some angles the light encounters no thin layers and no effect is seen, in other directions of view we see a bright blue, gold, green or multicolored surface. Looking at the sample of Labradorite rough pieces below you can see that only some of the "faces" are showing color at the angle at which they were photographed. The finest pieces have strong displays which skilled cutters take care to orient to best advantage for the face-up view. The lovely cabochon pair and brooch below show how bright and attractive the display can be, but if they were turned to a different angle, that beauty would temporarily be lost, only to return again as the pieces were moved in another direction.

[Labradorite feldspar rough, Labradorite cabochons, Labradorite brooch] **Check the web: One of the newest sources for attractive Labradorite is in Madagascar: go to this URL to see some of their specimens and a photo of the mine: http://www.madagascarminerals.com/pd_labradorite_rough.cfm Play of color: Iridescence in precious opal is correctly called "play of color" or "color play". The incorrect term "fire" is often misused instead--> recall from Lesson 4 that "fire" is an acceptable synonym for dispersion. But, at 154

least in this course, it is not an acceptable synonym for "play of color". What is taking place in opals, is not dispersion, but iridescence. We divide all opals (a huge group of gems) into precious and common, based on whether they have color play, or not, respectively.

[Precious opals: black opal:Image courtesy of GIA, precious Mexican opal, white precious opal pendant, matrix opal, "contra luz" opal (a rare type with a different display of colors in reflected versus transmitted light)] Play of color is seen as shifting patches of spectral colors on the gem's surface and/or in its the interior. This phenomenon is caused by the unique ultrastructure of the opal. The graphic below represents an interior view of opal at 25,000X via the electron microscope. Opal is made of spheres of cristobalite silica, SiO2(a polymorph of quartz). These are arrayed in closely stacked layers and have air, or more rarely, liquid, in between them. (To picture something similar on a larger scale, think of a crate of oranges with the fruit neatly arrayed into rows.) The openings act as diffraction gratings which split the light into colors, and the layered structure creates interference. As the light is reflected from the various layers the, now slightly out of sync waves overlap, decreasing or removing certain spectral colors, and reinforcing others. Thus, we get a shifting group of colors which flicker on and off, and move as we twist and turn the gem altering the light path and viewing angle. Which colors are seen is a function of the size and regularity of the spheres (with smaller spheres more blue is seen, with larger ones more red) and of our angle of view.

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[25,000x magnification of the structure of opal: Image courtesy of usgs.gov] In common opal, the openings between the spheres are so large that light doesn't have to bend when traveling through them, so that no diffraction takes place. Rather, the scattering and bouncing of light off the inner particles creates a sort of hazy effect commonly known as "opalescence". (Actually, opalescence is an example of another phenomenon called adularescence, see below.)

[Yellow common opal, showing typical opalescent haze] **Check the text: Pg. 222 in Lyman has pictures contrasting common and precious opal as found in the rough. **Check the web: This website has an in-depth discussion on the cause of color play in opals, with beautiful pictures:http://www.opalsdownunder.com.au/articles/colour Man-made iridescence: Taking a clue from Nature, humans have deliberately applied thin coatings or films of various kinds to the surfaces of gems to create iridescence. Although fragile, and to some tastes, a bit gaudy, these gems are popular. Two examples are the various iridescent topazes, the most common of which goes by the trade name "Mystic Topaz", and "titanium" drusy. In each case, a natural gem (a topaz or a quartz drusy) is coated with a microscopic layer of material (usually metallic) which creates the effect.

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[Mystic TopazTM, "titanium" drusy]

Adularescence: When a gem displays a billowy floating light which appears to come from below the surface it is showing adularescence. The name comes from the most prominent gem displaying the phenomenon: moonstone, known historically as "adularia". The term "shiller" or "schiller" is sometimes used to describe the light. Moonstone: In moonstone, adularescence is due to a layer effect, where thin inner strata of two types of feldspar intermix, (exsolution regions of sodium feldspar in potassium feldspar). These layers scatter light either equally in all spectral regions producing a white shiller, or as in the most valuable specimens, preferentially in the blue or the blue and orange. As in so many cases of optical phenomena the size or distance from layer to layer influences the colors we see.

[Adularescence in moonstone: white, blue and rainbow moonstones] **Check the text: The Hall text, (pg. 123) has a beautiful picture of a blue moonstone cameo-style carving (technically it might be termed a cuvette cameo-->but more about that in Lesson 7) Adularescence in other species: In other gems, the scattering shows up in a less dramatic form due to minute inclusions that scatter multiple wavelengths of light . In certain quartzes and opals, golden shifting light can be seen in the interior, which is sometimes called the "girasol" effect

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["Girasol" opal and agate] This general scattering of light, often is not distinctive, but rather shows up as subtle haziness, as in the case of the opalescence of common opal. Frequently we see the term "milky" used to describe individual specimens of a usually non-hazy species which show this type of adularescence. An exception is rose quartz which is virtually always hazy, so it doesn't need a special adjective, like milky, to distinguish it.

[Opalescent haze in common opal, "milky"quartz with pyrite inclusion,"milky" aqua, rose quartz]

Aventurescence: Unlike the other phenomena discussed so far which owe their beauty and distinctiveness to structural features which diffract or scatter light, aventurescence is a consequence of reflection. When disk or plate-like inclusions of another mineral are present, and are of a highly reflective nature such that they act as tiny mirrors, the gem sparkles and glitters. This glitter is called aventurescence. The term shiller, is also sometimes used to describe this spangly glow. The most common reflectors are copper, hematite and mica. The name is derived from the Italian word for "chance" or accident, and has no "d" in it! Quite frequently, even among those who should know better (like shopping channel hosts), the word is mispronouced as "adventurine". The most commonly encountered species showing this effect are certain feldspars and one variety of quartz.

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["Shiller"sunstone (copper platelets in feldspar), aventurine quartz (mica platelets)] "Goldstone", a man-made aventurescent glass with copper particles deliberately added to it, has been an inexpensive and popular gem imitation since Victorian times, and remains commonly in use today.

["Goldstone glass" in a Victorian brooch, circa 1880, and in a contemporary pendant]

Chatoyancy: This phenomenon is also due to reflection, but in this case, rather than involving plate-like inclusions scattered randomly, it is due to parallel thread-like reflective inclusions such as needles or tubes. When the inclusions are either not highly organized, or the gem is not cut in such a way as to concentrate or focus the light from them, we see a silky glow called simple chatoyance. Simple chatoyance: Tiger'seye is the most common gem that displays this phenomenon. Most pieces are a yellow to light brown color, but enhancements can create reds or other colors, and a naturally occuring variant called "hawk'seye" has a grey-blue to greenish color. **Check the text: In the Hall text, pg. 86 are pictures of a cigarette box made of hawk'seye quartz and a piece of hawk'seye rough. Less familiar to many, but greatly admired for their displays of chatoyance are the purple Charoites and the silvery grey serefinites.

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Corundum often contains rutile needles but frequently they are not abundant or organized enough to produce a star gem, and instead show up as a general silky glow, as seen in the ruby and sapphire carvings below.

[Gems showing simple chatoyancy: tiger'seye, Charoite, serefinite, ruby in zoisite, sapphire] The cat'seye effect: When the reflective fibers that create chatoyancy are aligned within a single crystal axis, and when the gem is properly oriented and cut as a domed cabochon, the reflections concentrate into a single band of light on the dome known as an "eye". Viewing this phenomenon is easiest with a single overhead source of light like sunlight, or a spotlight or penlight, and less successful with multiple light sources, or in dimly lit surrroundings. The pictures below show a close up of the parallel growth tubes in a rubellite tourmaline and the effect seen in that gem when it is viewed with proper lighting.

[Parallel growth tubes in a rubellite, that gem displaying its cat'seye: Images courtesy of GIA]

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Cat'seye gems have been popular throughout history, especially in the Orient. Cat'seye chrysoberyl is the most valued of all, and it has traditionally been given the honor of simply being called "cat'seye", whereas all other types, technically require a species modifier like: cat'seye tourmaline, cat'seye moonstone, etc.

[Just plain cat'seye (chrysoberyl), cat'seye moonstone] **Check the text: Pg. 76 in Hall shows a cat'seye aquamarine Fine quality cat'seye gems show some translucency, have a strong, well centered and straight eye and "do tricks". By that I mean: 1) with the light overhead, we see a strong eye 2) by moving the light source to one side and lighting the gem laterally, we get the "milk and honey" effect, (one side light, one side dark) 3) by using two lights and moving them from the center to the side, the eye will split into two bands each of which follows one of the light sources (opening and closing). These effects are shown in the pictures of the cat'seye (chrysoberyl) gem below:

[Cat'seye tricks: single eye, milk and honey effect, the beginning of the opening and closing effect as the single eye is splitting into two] The most commonly encountered cat'seyes are tourmalines, moonstones, chrysoberyl and quartz. Below is a selection of some gems that are extremely rare in cat'seye form:

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[Rarities: cat'seye Tanzanite, zircon and precious topaz] (OK, I'm going to irrevocably date myself with this analogy, but seeing all three of these rare cat'seye gems together at one time is the gemological equivalent of going to a concert where Jimmy Page, Keith Richards and Jeff Beck are all playing guitar on the same stage.) Asterism: This phenomenon is essentially a special case of the cat'seye effect, where the inclusions responsible for reflections are oriented parallel to more than one axis in the crystal. As with cat'seyes, the stone must be both properly oriented, and cut in a high dome to display the star. Depending on the nature of the inclusions and the crystal system of the host, a four or six rayed star will generally be displayed. By far, the most common star stone species is corundum, with quartz a distant second. Stars are relatively rare in other species. **Check the text: Both pgs. 31 & 112 in Lyman have pictures of the second largest star sapphire in the world: "The Star of Asia : 330 cts".

[Star stones: ruby, sapphire, white sapphire, rose quartz, (6 rayed), moonstone (4 rayed)] Food for thought: (The answer to this question will be found at the end of this lecture).

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Question 1: Cat'seye and star stones are generally used in rings and bracelets, rather than in brooches, tie pins, earrings or pendants. Why do you think this is so?

Color change: A color change gem is one whose color is substantially different when viewed with an incandescent light source as compared to its color as seen under daylight or a daylight equivalent fluorescent source. Due to this phenomenon's strong association with the Alexandrite variety of chrysoberyl, it is sometimes termed the "Alexandrite effect", regardless of which species is displaying it. **Check the web: I'm not sure how accurate this account may be, as I am no scholar of Russian history, but go to this URL for the most detailed version of the often told "Alexandrite discovery story" that I've ever read: http://createduniques.com/history/alex.htm Distinct from pleochroism, where the direction of view causes the color difference, true color change stones do not change color with a shift in viewing axis, but only with a change in light source. Due to their distinctive chemistry, stones which show this effect have very strong selective absorption in those regions of the spectrum where the two light sources differ most (that is, strong absorption in both the red and the blue). Daylight is rich in blues and incandescent sources are rich in reds --> so, although the stone could absorb both strongly, there is little blue in incandescent and little red in daylight to absorb. Hence we get different patterns of selective absorption, and see different colors. The completeness of the change is usually designated by percentage, for example, we might say that a particular stone shows a 70% color change. Although natural stones rarely show a complete color change, synthetic and simulant color change stones have been made which create the effect very strongly. In addition to Alexandrite chrysoberyl, other species which are occasionally found in color change forms are: sapphire, spinel, garnet, tourmaline and diaspore.

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[Alexandrite: incandescent (blue-violet), daylight (teal)

[Color change tourmaline: incandescent (mauve pink), daylight (purple)]

[Man-made color change glass "Tourmalike" rough: incandescent (slightly orangey pink), daylight (slightly brownish green)] Answer to the thought question for this lesson: (If you don't understand why this is the answer, then it's a good time to email me and ask!) 1) Cat'seye and star stones are oriented in such a way that their phenomena are well displayed on the center of the dome of the cabochon when light is hitting it perpendicular to the base of the cabochon. This is what happens when you hold your hand out to see a ring or bracelet (or when they are viewed in a jewelry display case), but gems that hang or are worn vertically do not show their phenomena to good advantage, as the light is mostly hitting the gem obliquely or parallel to the base. You have now completed the web lecture for the sixth lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Seven: Gem Fashioning

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LESSON 7: GEM FASHIONING Preparing a gem for use in jewelry, or for display as an ornamental object, is known as fashioning. In certain cases no fashioning is done at all; the gem material is used just as it came from Nature. For example, attractively formed crystal specimens or metal nuggets are sometimes put on display stands, or mounted in jewelry as is. Perhaps the most common example is pearls. These gems, which are already in beautiful shapes as found, are occasionally put into their mountings without even drilling a hole in them. When metalsmiths mount an unfashioned gem, strategically placed prongs, or special adhesives are used to make attractive and secure settings. The pictures below show some of the ways in which unfashioned gems are used:

[Danburite and bicolored tourmaline crystals glued into bezel "cap"settings, a baroque freshwater cultured pearl set in prongs, an uncut/unpolished macle "twin" diamond crystal bezel set in a ring: Image courtesy of www.furthers.com, Tahitian pearl glued to a dangle setting, natural gold nuggets soldered into channel setting] ** Check the texts: On page 31 of Hall and page 281 of Lyman are pictures of one of the most famous jewels ever made, known as the "Merman", or the "Canning Jewel", dated to the 16th century. Although the brooch is adorned with some fashioned gems, the pearl forming the torso is unfashioned. Along the same lines as the "Merman" is the pendant/brooch I recently had made from an unfashioned baroque freshwater pearl whose shape reminded me of a horse's head.

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[Baroque American freshwater pearl set with prongs and adhesive in a custom piece by jewelry designer Alex Horst] The vast majority of gems, however, are fashioned before they are used. The art and craft of fashioning gemstones is called lapidary (or diamond cutting), and a practitioner is known as a lapidary, (sometimes lapidarist), or a diamond cutter. Here's another instance where we see evidence of the split in the gem world between diamonds and colored stones; this time it's in theterminology used to describe the fashioning process, and to name the craftsperson involved in it. The History of Lapidary The roots of lapidary go back to the earliest history of human culture. The first of our ancestors that we can rightly say had "human" culture, developed crucial skills of knapping (flaking rock edges to make tools and weapons) and stone masonry. It was not very long after the fashioning and use of stone and organic materials for survival needs, that we find evidence of the beginnings of bead making, carving and engraving using those same materials. Not only do these artifacts tell archeologists that our remote ancestors had an aesthetic sense, they also signify how remote are the beginnings of the social and economic hierarchies so characteristic of humankind. How long have personal computers been a part our life? Maybe 30 years at most: my own first machine was acquired in 1980. In those thirty years most of us living in the "modern" world have learned some rudimentary skills and are using them to accomplish basic tasks. Some individuals among us, however, have become expert users of the greatest talent and sophistication. In today's world it might not be too much of a stretch to say computer savvy is a survival skill. So....

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Imagine a world in which rocks, and certain organic materials like bone, horn and shell, are not only ubiquitous but also necessary for survival. That world lasted for many thousands of years and the consequences of not mastering the technology were far greater than not getting a high paying job or being unable to download a tune or write a blog. During this huge period of time, humans developed highly sophisticated and successful techniques for working with these minerals and organic materials. Once the abilities were present, they were passed on, and improved as part of a people's cultural heritage. But how did they get started? The most likely answer is that our ancestors put to use what they saw happening in Nature around them! Simple observations like the smoothing effect of flowing waters and their sediments on stones, the sharp edges formed when certain sorts of rocks broke open, and the realization that some rocks could make marks or grooves on others could be made every day. These observations contained the information that led ultimately to the controlled use of abrasion, cleavage, fracture and hardness differences to shape, drill and decorate stones.

[Erosion at work rounding the edges of rock] It is not surprising that many of the first tools and ornaments were of the relatively soft, easy to work organics or minerals, such as wood, shell, amber, coral, horn, bone, turquoise and soapstone. **Check the text: On page 30 of the Hall text is a picture of a Stone Age obsidian ax, which the author says is "attractive as well as practical". Is it just me, or does anyone else fail to see how this item could be used to actually chop anything with?? :-)

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[Early Paiute twist drill for making shell or turquoise beads] One of the most pervasive themes I've encountered in my own review of lapidary origins is that the dates for various innovations keep getting pushed back further into pre-history as new archeological discoveries are made. Here are some recent examples of that, which, you might find interesting: 1) 75,000 year old drilled snail shell beads, were recently discovered in S. Africa, pushed the origin of the first jewelry back 30,000 years earlier than previously documented. (Original article: Henshilwood et al., Middle Stone Age Shell Beads from South Africa, Science 2004 304: 404 ). 2) **Check the web: Archeologists recently found a polished axe head from China dated to about 2500 BCE. This tool with a mirror-like shine on its surface was made largely of corundum. Both logic and laboratory simulations supported the idea that diamond (the only mineral harder than corundum) must have been used as the polishing compound--> prior to this find, diamond had not previously been documented to be in use until thousands of years later. View a summary with picture, of this article at:http://news.bbc.co.uk/1/hi/sci/tech/4555235.stm 3) **Check the web: The first documented use of a "compound machine" (two or more simple machines used in combination to do a job), in this case a lathelike device, comes from the recent discovery of ancient Chinese jade burial rings, dated to about 700 BCE, This find, pushes the use of such tools nearly 800 years back from the previously known date of the first century CE. Original article: Lu, Early Precision Compound Machine from Ancient China, Science 2004 304: 1638. View a summary, with picture, at:http://news.bbc.co.uk/1/hi/sci/tech/3792819.stm

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[Ancient Babylonian "melon" bead of lapis lazuli, circa 3000 BCE] Lapidary Products Tumbled stones: The simplest of way of fashioning gems, and that which serves as introduction to a lifelong hobby for many, is tumbling. The tumbler simulates, but speeds up many-fold, the natural events that make river stones smooth. It is accomplished by mixing the rough gems with water and a series of ever finer abrasives, and either tumbling them in a motorized, rotating rubberlined barrel, or subjecting them to prolonged vibrations.

[A rotary tumbler, a vibratory tumbler] As the stones hit each other and the abrasive materials, tiny cleavages and fractures occur slowly rounding sharp edges and corners. Each stage (usually 3 or 4) typically takes about two weeks so that from rough to tumble-polished gems takes considerable time. Tumbling is not a craft for the impatient. It can also be noisy and messy, but the product at the end is very pretty.

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[An assortment of tumbled stones] The smooth, shiny tumbled stones can be used as accents in aquaria, or as decorations in the garden, or in the pots of houseplants. They can also be glued to "bell cap" findings, and made into pendants, charms or keychains. They are sometimes drilled to make baroque beads. **Check the text: In the Hall text a tumbler and some tumbled stones are shown on page 28 Food for thought: (Answers to these questions are found at the end of the lesson.) Question 1: On page 28 of Hall in the discussion of tumbling, the statement: "gem fragments of similar hardness may be turned..." Why does the author specify that they must be of similar hardness? Slabs and slices: Sawing, with the exception, perhaps, of tidying up a mineral specimen or slicing open a geode, is seldom an end in itself, but rather a preface to polishing or further lapidary work.

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[Sawn amethyst geode weighing 10.5. lb: Image courtesy of Treasure Mountain Mining] Lapidary saws come in a variety of sizes from tiny facetors' trim saws with four inch blades, to standard rock slicing saws of 8 - 18 inches, to giant behemoths used to cut boulders.

[A small lapidary saw, a giant saw used in preparing jade boulders during the mining process: Image courtesy of www.jademine.com] Unlike the blades of more familiar wood saws, lapdiary saw blades do not have teeth per se. In fact, what we call sawing, in lapidary, is really a grinding process. The blades are generally thin round disks with an abrasive grit such as silicon carbide, emery, or diamond embedded into the rim.

[Lapidary saw blades, plain and "notched"] The rocks may be hand held or, more commonly, secured with a vice. Such saws must be used with coolant, usually some type of oil, to dissipate the great heat from the friction generated during cutting. Grinding and Polishing Once a gem has been sawn into slices or trimmed into manageable size, it is then ground to smoothness and polished to a luster. The grinding machines employ a metal, or in some cases resin, disk with its surface or edge covered with abrasives or polishes of various grit sizes and types. These disks come 171

in two basic styles: flat "laps" which are used horizontally, and upright "wheels" which are used vertically.

[A horizontal "flat lap" used primarily for slices and the bases of carvings and cabochons, a combination grinding/polishing unit with vertical "wheels" used primarily for producing cabochons] The basic idea here is the same as in tumbling, in that the gem is subjected to grits of increasing fineness as it is shaped and made smooth, then finally a polishing compound is applied which produces the finished shiny surface. The polishes are usually metal oxides or extremely fine grits of diamond. Various abrasives and polishes must be used to achieve success with different types of gem materials, based on their hardness and surface characteristics. Polished slices are sometimes used in jewelry, but more often are displayed as specimens, or ornamental objects such as bookends, wind chimes, or with translucent material, "sun catchers".

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[Polished slices of a bicolored tourmaline crystal will make lovely jewelry, like this contemporary brooch: Image courtesy of www.Fraleigh.ca, specimens of nodular variscite and chiastolite with cut and polished front surfaces used for display] Cabochons: Second only to faceted stones in familiarity as lapidary products, are cabochons (cabs for short). Most commonly cabs have flat bases and smoothly domed tops, and are fashioned from translucent to opaque materials. The cabochon form is particularly good at emphasizing the patterning of a gem, or for displaying most types of optical phenomena. They are usually produced with a slightly beveled bottom edge which makes for easier and more secure setting in jewelry. Sizes range from tiny accent gems to large pieces appropriate for use as belt buckles or in bola ties. Standard shapes such as ovals and rounds are commonly produced in "calibrated" sizes that fit exactly into commercial mountings. In other cases, particularly with rare or valuable material, or those intended for designer jewelry, the sizes aren't standard, and the shapes may be freeform.

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[Lapidary Keith Horst, cutting a cabochon of chrysoprase]

[Cabochons of standard form: round fossil ammonite, cat'seye apatite, carnelian set, long oval hydrogrossular garnet, boat shaped Bruneau jasper] Some common variants of the cabochon form include gems cut with a series of curves that meet on top to form an apex rather than a standard smoothly curved dome, and those whose top is a flat table, a type usually referred to as a "tablet". Cabs of very dark translucent material, like deep red almandite garnet, are sometimes cut with the back hollowed out to lighten their color. 174

[Covellite cab with an apex top, tablets of amethyst and dendritic chalcedony] Beads: Beads are one of the most ancient types of fashioned gems, and are enjoying an enormous resurgence in popularity today. There are beading magazines and books galore, and most towns of any size have stores that sell beads along with supplies for stringing them. The Lapidary Journal, the most widely read, monthly general lapidary magazine, each year devotes it's October issue to beads. Beads are simply gems with holes in them. The fashioning of a round or other symmetrically shaped bead can be done by hand with cabbing equipment, but in commercial operations is usually done with a device called a "bead mill". Sawn slabs are cut into cubes (for a round bead) and fed into the mill which has grindstones that operate at angles to the cube removing its edges until it is uniform. Most mass produced beads then go into a tumbler to be polished and are drilled with a lapidary drill press, using diamond tipped drill bits. The hole can be completely through the gem, or only part way through, in which case it is said to be "half drilled". Most commonly half drilled beads are used for stud earrings, rings or dangles. Depending on which direction they are drilled (side to side or top to bottom), and whether the drilling is centered or not, full drilled beads find various uses such as in bead strands and as dangles. Beads can be virtually any shape: round, oblong, tubular, flattened circles (rondells), briolettes, fancy or baroque.

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[Side to side drilled pearls, half drilled pearls, tubular turquoise beads with pearls]

[Top to bottom drilled jet beads for dangles, non-centered side to side drilled carnelian briolettes for dangles]

[Fancy cabochon bead, rondell strand of Mexican opal, baroque (tumbled) bead strand of howlite] Engraved and Carved Gems: Gems fashioned by engraving are incised, so that a design is cut (shallow or deep) into their surface, whereas carved gems are fully three-dimensional. Engraving and carving should be considered lapidary arts rather than crafts, as the vast majority of styles and pieces can only be done well if the maker has some degree of artistic talent, an ability not required of those doing tumbling, cabbing, or bead making. Although the majority of such pieces are orginal works of art, more and more use is being made, especially in commercial production of gem carvings, of ultrasonics and lasers which are sometimes computer-assisted, and may be used to produce many exact replicas of a single original carving. Engraving and carving gems is, like bead making, a very early form of lapidary. Historically, such pieces were done by hand with bone, stone, or metal tools and suitable abrasives. The choice of tools was dependent on what was locally available, and on the hardness of the material being worked. There are still a few hand carvers who carry on this tradition. For the most part, though, today's gem carvers and engravers use electrically powered tools with silicon carbide or diamond tipped implements. One of the most commonly used tools for carving and engraving is the "flex shaft" which consists of a motor which drives a pen-like device with a rotary 176

head that can be fitted with dozens of different cutting, drilling, carving, sanding and polishing tools.

[A flex shaft tool with an assortment of "bits"] When using a flex shaft, which is usually hung on a stand and operated by a foot switch, the item being worked is mounted in a vice or held stationary in some way while the rotary tool, held like a pen in the hand, is used to grind or polish it. Alternatively, many artists favor a reversal of this system whereby a "fixed arbor" which contains the rotating tools sits on their bench, while they hold the item to be carved in their fingers, and apply it to the tool.

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[Gem carver, Alex Horst, using a fixed arbor for carving a citrine--note water drip and the differently shaped diamond tools used in each picture] A great master in the art of gem carving, Donn Salt, who specializes in New Zealand nephrite jade and other local stone materials, provides, on his website, a step by step journey through the process of creating this artwork, "Uroboros" which is based on a Maori traditional form.

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**Check the web: Have a look: http://www.donnsalt.com/UROBOROS/Uros_docs/Uroboros_00_enter. htm With such a long history, it is not surprising that a large number of different carving styles, as described below, have been developed and made popular. 1) Intaglio: In these gems, a design is cut into the gem, so that it lies below the rest of the gem's surface. Historically they were worn in a ring which was also used to form a signature seal. Intaglios have always been most popular in men's jewelry.

[Circa 1st century BCE Roman chalcedony itaglio (set into a contemporary ring), and the impression made by it in clay: Image courtesy www.bcgalleries.com.au, Victorian Era man's hematite intaglio ring: Image courtesy of Sunday and Sunday Antiques, a sard "cuvette" (a type of intaglio or other carving which is cut into a concave depression in a gem)] 2) Cameo: Cameos are essentially the reverse of the intaglio idea, in which by cutting away the material around it, the design is raised abovethe level of the base. The most common subject matter was (and still is) beautiful ladies or historical or religious figures in profile, and the materials used frequently have differently colored layers which can be strategically revealed in forming or embellishing the image. Historically, shell and agate were two of the most commonly used cameo materials, although there have been bursts of popularity of a great many other materials like jet, coral, and even lava!

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[Contemporary shell cameo, antique "hardstone" agate cameo ring, Victorian lava and coral cameos: Images courtesy of Acanthus Antiques] 3) Scrimshaw: In this technique a design is shallowly engraved into the surface of horn, bone or ivory then inked, or painted to provide contrast or color. Scrimshanders have a long history, particularly among those peoples who traditionally hunt either marine mammals, elephants, or other herbivores with antlers, horns or sizeable teeth or tusks.

[A 19th century American sperm whale tooth scrimshaw pendant, a contemporary painted scrimshaw (on legally collected elephant ivory), a contemporary Native American scrimshaw (on legally collected whale baleen)] **Check the web: If you, by chance, have an interest in the current US and International regulations regarding the importation and/or sale of raw ivories and their artifacts, you can visit this URL for an authoritative report:http://www.boonetrading.com/Pg18.html 4) Surface engraving/carving: In this technique a cabochon is decorated with designs carved into it (front, back or all round). Highly transparent material is sometimes "reverse" carved where the design, usually left unpolished, is cut into the back to create a picture visible from the front. The three

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dimensional scenes which result require great skill to accomplish, and can be stunningly beautiful.

[Surface carved aquamarine, emerald, and moonstone cabochons, reverse carved rock crystal quartz, amber and rock crystal quartz (note inset opal "sun")] 4) True Carving: When the cutting or engraving work encompasses all sides of the piece so that it's truly three dimensional, it is said to be a carving. The four most common styles for carvings are hololith, representational, stylized, and abstract. Hololiths are hollow, three dimensional jewelry pieces, usually rings or bangle bracelets that have been carved from a single piece of stone. Some of the most charming of these consist of two or more interlocked pieces. Food for thought: Question 2: The vast majority of hololith gem creations (especially the interlocking ones) have historically been made from jade, with a smaller number constructed from jaspers or chalcedonies. Why do you think these materials are favored? Representational carvings are meant to resemble the subject as closely as possible. In stylized carvings, we recognize the subject matter, but the artist has put their own interpretation on it. Abstract carvings are made as pure expressions of form with no overt reference to real objects.

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[Hololiths: jadeite interlock bracelet, a "poppy jasper" bangle bracelet]

[Representational carvings: chalcedony octopus, coral roses]

[Stylized carvings: lapis lazuli rattlesnake tail, turquoise horse]

[Abstract carvings: blue chalcedony, sugilite, jasper] Faceted Gems: The most popular fashioning style for transparent gem material is the faceted gem. Because colored stones and diamonds are cut by different methods, and graded and marketed separately, we'll look at each in turn, although some of what is covered below applies to both. Colored stones: When discussing a faceted stone, the first distinction that is often made is shape (face up outline). As is also true of diamonds, colored stones are either rounds or fancy cuts. So ovals, pears, freeforms, etc. are all "fancy". Going beyond the outline shape, one might next look at the cutting style. There are three traditional basic styles (brilliant cut, step cut and mixed cut), with many old and new variations upon them. 182

The brilliant cut which is especially suited for producing light return to the eye (brilliance), has triangular and kite shaped facets. The step cut, which is more suited for emphasizing color in a gem, has tiers of rectangular to square facets. Mixed cuts usually have a brilliant style crown with a step cut pavilion, but the opposite arrangement can be seen as well. Occasional variants include faceted gems with an apex rather than a flat table, and those whose crown is formed of rows of parallel facets (opposed bar cut) or a field of intersecting squares or diamonds (checkerboard cut). ** Check the text: Pgs. 69 - 72 in the Lyman book, have top and side view diagrams of a large variety of faceted styles.

[Oval brilliant cut amethyst, square step cut amethyst, oval mixed cut blue zircon]

[Apex cut square Mexican opal, rectangular opposed bar cut citrine, rectangular cushion checkerboard cut iolite] Less frequently seen variations of the faceted gem are buff tops, briolettes, concaved cuts and fantasy cuts. A buff top gem has a faceted pavilion with a smoothly domed (cabbed) crown. An interesting magnifying effect of the pavilion facets is achieved by doing this. The briolette (mentioned earlier as a popular bead style) is a three dimensionally faceted gem, usually in a pear or tear drop shape. Concave cuts have, logically, concaved or sunken in facets on either the crown or pavilion or both. This technique increases overall light return and creates unusual reflective patterns and/or face-up outlines. The "laps" which are used for concave cutting are cylindrical. Relatively few facetors have the equipment and expertise necessary to produce stones of this sort. Extra time to attain a good polish, and more 183

expensive equipment are two factors which tend to set a premium price for such gems. Fantasy cuts have carved areas on the crown or pavillion, which may be polished, or left unpolished to create special effects. Food for thought: Question 3: Why would it take longer to get a good polish on a concave facet than on a flat one?

[Buff top pear shaped citrines, a selection of briolettes: Image courtesy of www.briolettes.com]

[Concave cut Swiss blue topaz, showing both the dramatic reflective pattern and the"scalloped" outline which can be seen in concaved gems, fantasy cut London blue topaz, fantasy cut citrine with unpolished carved channels on the pavilion to create a "bullseye" effect] The Faceting Process Faceting is the newest of the major lapidary crafts. Historically, we don't find the first faceted gems until the 14th century and faceted diamonds don't make an appearance until the 16th century. The earliest cuts were done by hand, and had just a few facets. An example of an early, but still occasionally used cut, is the rose cut which was often chosen for early diamond jewelry. The rose cut has a flat bottom like a cabochon, with a series of facets rising to form a dome or apex.

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Several hundred years ago the jamb peg faceting machine came into use, and faceting, as we recognize it today, began. In order to cut facets on a gem in an organized manner that results in a precise arrangement, three factors must be controlled: 1) the angle of the cut 2) the depth of the cut and 3) theradial placement of the cut. Although modern highly engineered faceting machines have replaced jamb pegs in much of the world, these older systems are still widely used, and a substantial proportion of the gems in commerce today have been cut by them. Check the text: Pages 59 - 61 in the Lyman text show diagrams of some early cutting styles

[Typical antique rose cut diamonds in a circa 1840 brooch (the diamonds in this piece were probably already antique when it was made): Image courtesy of The Fraleigh Collection, and a modern-day rose cut diamond in a contemporary "antique style" ring: Image courtesy of www.antiquediamond.com] Background Information on Faceting Pavilion and Crown: In the faceted gem, the pavilion and crown have different functions. The crown acts as a window or lens to collect the light which strikes it, and direct or focus it into the pavilion of the gem, whereas the pavilion must act as a mirror to reflect that light around the pavilion, and then back to our eyes through the crown. If the pavilion fails to do so, the gem lacks brilliance and is lifeless. Crown angles are much less crucial to the optical performance of a gem than are those of the pavilion, and can vary substantially from stone to stone without severely affecting a gem's brilliance. The crown and pavilion are cut in two separate sequences of operations. The gem is initially adhered to the "dop stick" until one side is finished, then removed, turned exactly 180 degrees, and attached to a new dop, to go through corresponding operations for the other side.

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The Critical Angle: Each gem species, depending (with an inverse relationship) on its refractive index, has a pavilion faceting angle below which it loses brilliance. Think for a moment of skipping flat stones on water. What controls whether the stone will skim and bounce along the surface, or go kerplunk into the depths?.......The angle at which it hits the water! So it is with light that enters a gem and strikes the pavilion facets. When that beam hits outside the crtical angle it will be reflected to another facet and/or to the crown, but if it hits inside the critical angle it will not reflect, but pass right out through the side or bottom of the gem, not to return to our eye-->the gem loses brilliance. In the graphics below we see two gems cut to the same proportions (pavilion main angles at 38 degrees) one is a diamond (RI = 2.42), the other is a fluorite (RI = 1.43). The critical angle for diamond is about 24 degrees, that of fluorite is 44 degrees. At 38 degrees on the pavilion facets much of the light hitting the fluorite is lost, whereas almost all that which hits the diamond is reflected. The diamond would appear bright and the fluorite lifeless, especially in the center: we would say it has a "window". If, instead, we were to cut the fluorite to a pavilion angle of 45 degrees or above, we would then eliminate the window and it would be brilliant, and conversely we would get a lifeless diamond if we were to cut its pavilion at 20 degrees or below.

[Reflection when the pavilion angle is above the critical angle, lack of reflection "windowing"when it is not: Graphic courtesy of Joe Mirsky] In the first picture below you can see two similar looking gems (each is light yellow and rectangular). The golden beryl gem on the left was cut with its pavilion facets above its critical angle, and it appears brilliant, the yellow spodumene on the right was cut with the pavilion facets below its critical angle and has a "window". We call it a window because the light passes right through it, like window glass, so that you can easily read the printing underneath. The second set of pictures shows a top and bottom view of a 186

badly windowed topaz. You can see how shallow (low angle) the pavilion is. In order for this gem to be fully brilliant, the necessary recutting would reduce it's face up diameter and carat weight substantially.

[Non-windowed and windowed gems]

[A windowed topaz gem with a very shallow pavilion: Images courtesy of thaiambergems.com] **Check the text: On pages 76 & 77 of the Hall text, note the large windows in many of the faceted beryl gems on those pages. Actually just about any of the gem pages in either text will show examples of windowed gems. Yield vs Brilliance, Clarity and Color: Faceting is a series of compromises. The yield, that is the carat weight, of the finished stone versus the carat weight of the rough, can be as high as 40 - 50% or as low as 1-2% depending on a mix of the attributes of the rough, and of decisions that are deliberately made by the facetor. For example: 1) The shallower the pavilion angles, the greater the yield (but the less the brilliance). 2) Included rough can be oriented (with loss of yield) to eliminate or minimize the appearance of inclusions. 3) Pleochroic stones will give different colors and different yields depending on how the stone is oriented for cutting. 4) Rough that happens to be somewhat "gem shaped" yields more than thin and flat, or highly asymmetrical rough. 187

Given a moderately well shaped, clean piece of rough, which is cut to correct pavilion angles, the average yield is about 20%. To put it another way: start with gem rough = 5 ct, end up with finished gem = 1 ct. Faceting Tools In the figure below you can see the basic set up of a traditional jamb peg faceter. The spinning lap provides the grinding and polishing surface, the wooden "dop" sticks to which the rough is adhered, serve to hold the stone in position as various cuts are made. The angle of the cut is controlled by placing the dop stick in a particular hole, the depth of cut is controlled by the amount of time the piece spends in contact with the lap and how hard the facetor presses down on it, and the radial position is controlled by removing, slightly rotating, and reinserting the dopstick in its hole as each different cut is made. Most stones that are cut on such equipment are referred to as "native cut".

[A jamb peg faceting machine] A modern, highly engineered faceting machine is seen below: such machines accomplish the same three goals (angle, depth, and radial position of facets), but do so with great accuracy. In machines of this type the dop stick with the gem attached to it, is fitted into a "quill" which can be postioned at various precise angles via the "protractor". The quill moves up and down on the mast, which gives great control over the depth of cut, and a slotted index gear gives accurate control over the radial placement of facets. Stones cut on such equipment are usually described as "custom cut". Before summarizing the differences between the products of the two types of machines (which is going to make the native cut gems sound pretty lame), let me say that it takes long training, and tremendous skill to be able to produce a 188

nice looking gem with a jamb peg, whereas virtuallyanyone who can read the lapidary equivalent of a cookbook can produce an acceptable stone with modern machinery!

[A typical modern faceting machine: Image courtesy of Ultra Tec, the main working parts of a faceting machine] Native cut gems: These are generally cut by eye, usually in Asia, Africa or S. America, on a lap, or more often a jamb peg or similar machine. The cuts are typically oval to cushion shaped with windows, low crowns and bellied pavilions. The "make" (proportions and finish) is "inferior" in that the table sizes, crown heights, pavilion depths, facet meets and degree of polish are not to custom standards. Such cuts give high yield from gem rough, and due to the increased volume/mass of the pavilion tend to deepen and emphasize color. For these 189

reasons the majority of the high value colored gem rough (ruby, sapphire, emerald, Imperial topaz, etc) is still cut this way-->even though the cutters could make smaller, brighter stones with the equipment they have. Frequently native cutters are paid by yield, another factor which perpetuates the native style of cutting. A few native cutters working in certain gem factories (such as the one pictured below) pride themselves on producing custom-style gems, a feat all the more impressive given the equipment available to them. Every angle and facet placement is determined by eye alone!

[Native cutters in Vietnam, working on spinel and ruby, one of their customstyle gems, a pink spinel: Images courtesy of www.gemsfromearth.com] Custom cut gems: These are usually produced on some type of precision engineered faceting machine (there are many brands), usually in N. America or Europe, using magnification. Cuts can be any shape, but are characterized by "superior make". The gems are usually fully brilliant with no windows and pleasing crown to pavilion proportions. The level of polish, and the precision of facet meets is very fine. Such cutting sacrifices yield, and may lighten the color tone of gem material. On the other hand custom cut stones are generally easier to set in commercial mountings, and extremely beautiful due to their brilliance and symmetry. Faceting Paraphernalia: Various adhesives are used in faceting, such as epoxy resin, cyanoacrilate "Super Glue", and faceting wax. Different gem cuts require different index gears, the one below has 96 slots and can cut gems with 3, 4, 6, 8, 12 and 16190

fold symmetries (other indices would be used for gems with 5 or 7-fold symmetries). The dops are commonly made of brass and come in a large variety of sizes. Seen below are three: a flat, a cone, and a "vee". Each is used for rough of certain shapes, or during different points in the faceting process.

[Lapidary adhesives (epoxy, "super glue" and facetors' wax), a faceting index gear, brass dops] The laps used for cutting and polishing come in a variety of materials and sizes. The first picture below shows two diamond-surfaced cutting laps: the one on the left has a coarse diamond grit embedded into its metal surface, it would be used to lay in the basic shapes of the facets, the other one has finer grit and would be used to smooth the facets and prepare them for polishing. The second picture shows a polishing lap which is made of a plastic resin with fine metal particles embedded in it, very fine grit diamonds (in solution) are sprayed onto the lap surface for polishing the gem. Metal oxide slurries or sprays (such as cerium or aluminum oxides) can also be used for some gem materials.

[Diamond cutting laps: coarse and fine; resin-metal gem polishing lap with diamond sprays] 191

The "faceting cookbook": Although some facetors do freehand cutting or design and execute their own special cuts, most follow diagrams that indicate the angles, number and cutting sequences for the facets. (Due to critical angle differences, the directions for a round brilliant topaz would have slightly different angles than those for a round brilliant quartz). In the graphic below "B" = bezel facets, "M" = main facets, "S" = star facets, and "T" = table. ID indicates the "12 o'clock position" for the index gear. (On the left is the pavilion cutting diagram, and on the right the crown cutting diagram).

[Round brilliant faceting diagram: Graphic courtesy of www.theimage.com] For example, the first instruction in such a facetor's "cookbook" might say (for quartz) "Cut 8 equidistant 42 degree facets as the pavilion mains, so that they meet to form a culet". This would be followed by something like: "At index settings on either side of the main facets, cut 16 bezel facets at 44 degrees". The directions would continue through the entire cutting process-> like following a recipe in a cookbook! Actually, there is a bit of finesse to it, and quite a lot to learn, but faceting is nothing which requires high level mechanical, manual dexerity, or mathematical skills, and is enjoyed by many as an interesting hobby.

[Like magic! From rough sapphire to custom faceted gem: Images courtesy of www.customgemstones.com.] 192

**Check the web: To see the full sequence of steps involved in cutting this gem, go to: http://www.customgemstones.com/GEMCUT/GEMCUT.HTM To emphasize my point that faceting should not be viewed as an especially intimidating craft, here's a picture of a successful new facetor: the 10 year old grandson of well respected cutter, Barry Bridgestock. The stone shown is his second production, and he did have guidance from Grandpa but.....not bad!

[Jake Bridgestock, age 10, facetor, a blue topaz cut by Jake] Diamond cutting: Considerably more talent and expertise is necessary for diamond cutting than that required of the colored stone facetor. In order to successfully cut diamonds one must be able to look at a piece of rough and determine its crystallographic axes. This knowledge is then used in choosing the best cut to use, as well as in orienting and cutting the various facets, which must be ground in different directions on the lap, depending on their variable hardness. The cutters must be adept at getting maximum yield while still retaining good brilliance. A 1-2% difference in yield would be small potatoes for most colored gem cutters, but in the case of a diamond, many dollars could hinge on it. A "natural", a small unpolished area left on the girdle of a diamond, far from being a blemish, is a considered a sign of superior cutting--> meaning that the cutter has gotten the biggest stone possible from a particular piece of rough. In today's diamond cutting industry computerized angle analysis, 193

and computer assisted design (CAD), is often used to help cutters maximize yields. In order to get the highest yields, most diamonds are cut with slight to moderate deviations from the "ideal" proportions, resulting in some loss of brilliance and/or dispersion. There are diamond cutting firms, though, which specialize in "ideal cut" diamonds. These stones are, on average, at least 10% more expensive per carat than "run of the mill" diamonds. In truth, only a well trained eye can detect these subtle differences in proportions, dispersion and brilliance, but as with any product, there are those who are eager to have the "very best", and quite are willing to pay extra for it. **Check the text: Page 64, Figure 26, in the Lyman text shows how exacting in terms of angles and percentages is the "ideal" cut for a diamond. The equipment used in diamond cutting is heavy duty, reflecting the tremendous forces and long periods of time necessary to cut and polish this hardest of all materials. The lap, called a "scaife", is made of cast iron, and revolves at about 3000 rpm. Diamond "bort", in oil, is used for cutting and polishing. The stone is held by a "tang" which is a claw-like mechanism (no adhesive could withstand the intense heat generated by cutting). The cutting and polishing process is really one of simple (but painstaking) abrasion as the tiny diamond crystals in the oil, being forced against the rough with great speed and pressure, successively wear away minute bits of diamond from the surface, gradually making it more smooth and uniform. Because the bort particles are randomly oriented, there are always at least some whose exposed crytal faces are harder than the surface to be polished (this is true as long as the diamond has been properly oriented for cutting to begin with--> its own hardest crystallographic axis cannot be directly parallel to any facet.) The directions in which a diamond can be polished are called its "grain" and there are three basic types of rough (and many variations on those) each with a different pattern of grain directions. During the cutting process, as the different grain areas are brought to the scaife, the direction of the polishing must be altered. Twinning in diamonds can greatly complicate the cutting process as there will be an overlapping of harder and softer axes. Only a few firms specialize in cutting twinned crystals.

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Diamond cutting centers in New York, Bombay, Antwerp, and Tel Aviv produce the large majority of the world's diamond gems.

[Cutters in a diamond factory in Antwerp: Image couresty of Daems Diamonds] Although there certainly are "master" cutters who can start with a piece of diamond rough, and go through all the steps to produce a finished gem; in the commerical world of diamond production, the process is usually divided into stages, each of which is accomplished by a specialist in that part of cutting. 1) Marking: The "marker" studies and then marks the rough to direct the removal of inclusions, and indicate how the piece should be cleaved or sawn. For large, extremely valuable pieces, this stage may take weeks or months.

[A diamond being prepared for cleaving or sawing by the "marker": Image courtesy of Daems Diamonds] 2) Cleaving and/or sawing: Although most of us can picture that tense moment when the "cleaver" swings his mallet and strikes the wedge that will separate a diamond along its cleavage plane, in reality, few diamonds are cleaved today. The average piece of rough is sawn (by diamond blade or laser) into suitably sized and shaped pieces by the "sawyer". Cleaving is still important with large rough however.

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[A diamond being cleaved, one being sawn: Image courtesy of Daems Diamonds ] 3) Bruting: The job of the "bruter" is to create the face up outline of the gem: round, oval, marquis, etc. The time honored technique for doing this involves using one diamond to grind another and is done mostly by eye using a lathe-like apparatus. When bruting is done with too much force, or too much heat is allowed to build up, tiny whisker-like feathers can be seen around the girdle of the stone. This is a blemish called a "bearded girdle".

[The bruting process: Image courtesy of Daems Diamonds, a diamond with a "bearded" girdle] 4 & 5) Blocking & Brillianteering: The "blocker's" job is to create the basic shape and proportions of the gem by cutting the table and culet as well as the crown and pavilion main facets. The "brillianteer" (the cutting superstar), traditionally puts in the stars, and the crown and pavilion bezel facets, each one of which may require subtle adjustments of angle, direction and size, depending on the grain pattern of the individual stone, its inclusions, and the desired cut.

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[A diamond in the cutting process, note the tang holder and the spinning scaife: Image courtesy of GIA]

[Before and after: a rough diamond, a brilliant cut diamond: Image courtesy of thaigem.com] Answers to the thought questions for this lesson: (If you don't understand why these are the answers, then it's a good time to email me and ask!) 1): If the gems being tumbled together are not all of approximately the same hardness, the softer ones will not only be worn down by the abrasive grit in the barrel, but also by contact with the harder stones in the mix. In my own first tumbling effort many years ago, when I did not know this, I opened the barrel after a couple of weeks, to find some of the gems (the harder ones) just barely worn, and some of the softer ones almost gone! 2): Aggregate materials like jasper, agate, chalcedony and especially the jades: nephrite and jadeite, are very tough, which means that they will not easily break when the forces of the carvers' tools are used to make and/or separate relatively thin areas. This is particularly true for interlinked forms which require a lot of force on a small "thread"of material attaching one piece to another. Single crystal materials, being less tough, break much more easily. 3: In order for a gem to have a good polish the surface must be made absolutely uniform, and smooth to a microscopic degree. Polishing a curved surface to this level, is much more difficult and time consuming than doing the 197

same with a flat one. Picture as in woodworking, for example, trying to sand a flat table top, versus sanding a curving table leg and trying to get each of them perfectly, and uniformly, smooth. You have now completed the web lecture for the seventh lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Eight: Gem Enhancement

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LESSON 8: GEM ENHANCEMENT Enhancement is defined as any processing (other than fashioning) which improves the appearance or durability of a gem. Determining whether or not a gem is enhanced is part of the previously discussed aspects of gemological investigation: 1) Species: What is this gem? 2) Origin: Is it natural or synthetic? 3) Treatment: What enhancements, if any, has it received? Just to think about: Does it matter if a gem is enhanced? So what, if a gem is enhanced? If enhancement makes it prettier, or more durable, what's the big deal, and why do we even need to know? Here are some of the major issues to consider: •

Enhancement can alter the value of a gem up or down. If it makes an unuseable piece of gem material useable, or an ugly one pretty, then it has increased the value of that particular piece. On the other hand, the reality of the marketplace is that "absence of treatment"in itself, has value. (Why this is so has to do both with rarity, and with a certain philosophical value many accord to the unaltered products of "Mother Nature".) Take two equally clean, natural origin rubies of exactly the same size, cut and color: one has the color it came out of the ground with, the other is a piece that originally was a less attractive color, but has been color enhanced by heating. In today's market the unenhanced stone would bring from 10 - 20% more per carat. **In this case, the reasons for needing to know about a gem's treatment status are economic and philosophical.

•

Although many enhancements produce permanent changes, others are unstable and fade, wear away, or alter with time and exposure to environmental factors. The man-made iridescent topazes that were discussed in 199

the last lesson are good examples here. The coating is microscopically thin, and care must be taken to preserve it. On the other hand, the blue colors of irradiated and heated topazes (like Swiss and London blue), are permanent and stable, and these gems do not require any different level of care than naturally colored ones. **In this case the reasons for needing to know about a gem's treatment state are practical. The general feeling among gemologists and ethical gem merchants is that there is nothing wrong with any type of enhancement, as long as it is fully disclosed (including care instructions), and the gems are appropriately priced to reflect their treatment status. Unfortunately, there are many "ethically challenged" companies and individuals which seek to profit by doing neither of these. Two Important Organizations with an Interest in Gem Enhancement: FTC: The Federal Trade Commission regulates many basic aspects of marketing, advertising and commerce in general. For gems and jewelry, the pertinent regulations regard certain aspects of advertising and describing gems, as well as issues of gem weights and measurements. AGTA: The American Gem Trade Association is an industry organization of carefully screened colored gemstone dealers who are based in the USA. Attaining membership in this organization involves a lengthy and rigorous vetting process meant to assure that only dealers who ascribe to the highest standards of ethical business practices can belong. This organization has had extreme influence, world-wide, primarily by developing and publicizing standards of ethical business practices for colored stone dealers, especially as regards disclosure of enhancements. AGTA guidelines for gem advertising and marketing go well beyond the generalized and generic ones found in the FTC regulations. Because more and more countries are adopting the AGTA guidelines and their coding system, or patterning their own after it, we will be covering portions of it in this class. Background:

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Think of knowledge about gem enhancement to be as a series of positions on a continuum from 100% known to be enhanced, to 100% known to be unenhanced:

On the one end are gems that we know, 100% for sure, are enhanced. This might be because the treater has presented the material to us as enhanced, for example: the invoice says "heat treated sapphire" or "dyed chalcedony". It could also be because in examining the goods we find incontrovertibleevidence of enhancement. For example: microscopic examination of a diamond reveals the characteristic tunnels made by lasers for purposes of clarity enhancement, or testing the surface of a gemstone bead with a swab dipped in acetone removes some of the blue dye from it. On the opposite end are gems that we know, 100% for sure, are unenhanced. This category is pretty small actually, as unless you "dig it yourself", you are taking the word of someone else as to the gem's treatment status. (Even in this case, it is possible that the enhanced gem rough could have been "salted" into the natural source!) Not all enhancements can be revealed by current testing methods, so in some cases a thorough (and costly) examination by a trained professional might only give the equivocal result of: "no evidence of enhancement found", which is not the precisely the same thing as "unenhanced". Many low temperature heating processes, and some forms of irradiation are literally undetectable with today's technology. They leave no tangible signs distinct from those which might have been the result of natural environmental factors.

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Inbetween these extremes, lies our degree of knowledge of the treatment status of most gems: three major stopping points on the continuum might be labelled: • • •

Assumed to be enhanced Probably/Possibly enhanced Assumed not to be enhanced

Gems which are assumed to be enhanced are those species in which enhancement is the standard practice, or those which don't exist, to any extent, in Nature in the treated color or form . Examples would be blue topaz, and black onyx which are found in only tiny quantities in Nature, but produced in huge amounts by irradiation, and dyeing, respectively. This category would also include oiling of emeralds, a process used on more than 90% of emeralds in commerce. Gems which are probably or possibly enhanced are those for which known treatments exist, but range from being commonly to occasionally used. Examples would be resin "stabilization" of turquoise, bleaching of pearls, dyeing of jade, and heating and/or irradiation of beryls , quartzes and tourmalines. It is in this situation that familiarity with the detectable signs of enhancement can be most useful. A major goal of this lesson is to acquaint you with some of the most important of these. Gems which are assumed not to be enhanced include those for which no treatment has yet been discovered for the material (or at least none that is cost effective and non-destructive). This category is highly provisional as new enhancement processes may be developed or their safety or economics improved at any time. Examples of gem species which currently can be assumed to be unenhanced are: spinel, iolite, sunstone and most types of garnets.

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[2 general and 12 specific AGTA codes to be familiar with] History of Gem Enhancement: The quest to make gems look better, last longer, or sell at a higher price is nothing new!: •

• • •

•

As far back as 2000 BCE the Minoans applied thinly beaten gold foil to the back of transparent stones to make them more reflective. Amongst the treasures buried with "King Tut", circa 1300 BCE, were heat treated carnelian gems. Pliny the Elder (23 - 79 CE) in his famous work "Natural History" gives recipes for oiling and dyeing gems. An early "consumer advocate", Camillus Leonardus, an Italian physician and scholar, in a work called "Mirror of Stones" published in 1502 gives tips on spotting treated gems, like using a file to test for hardness, and hefting a gem to determine its specific gravity. By 1932 a gemological paper had been published listing fourteen known heating treatments.

Just as is true today, some of the motives of the gem treaters were honorable, and some were not. 203

Major Gem Enhancements The surveys that follow show a few examples (there are many, many, more) of some of the most common and economically important gem treatment processes. In some species the treatment is used occasionally, in others it is common, and in still others it is standard. The organization of the species presented, within each of these treatment type surveys, is simply alphabetical, not in order of dollar value, or frequency of use.

Heating: (AGTA Code = H) The most versatile and widely used treatment for gems is heating. Depending on the gem and the desired effect, temperatures used vary from those provided by placing the gems in direct intense sunlight, to near melting point temperatures of 2000 degrees C; periods of heating range from minutes to several days, and oxygen may be present or excluded from the heating atmosphere. The atmosphere in which the gem is "baked" is important, as it will influence whether its ions gain or lose electrons. That is, it will determine if a chromophore ion will be changing from Fe3+ ---> Fe2+ or vice versa. A "reducing" atmosphere (one without oxygen) which can either be supplied via a high tech furnace, or simply by placing the gems to be treated in a closed container with charcoal), causes the number to go down (+3 to +2 for example). In an "oxidizing" atmosphere (oxygen present) the number goes up. (**You will recall from the discussion of the causes of gem colors in Lesson 4, the importance of the ionic state of the chromophore.)

Heating amber: Amber is heated for three main purposes: to darken it, to clarify it, and to deliberately add stress fracture inclusions. When heated at low temperatures the surface of amber gradually darkens over time. Much of the clear amber found in nature is a light yellow to gold color, but shades from tan to gold to orange to dark brown can be obtained by heating. The color is usually confined to a surface layer and so is often done after the gems have been fashioned. If desired, the surface layer can then be partially polished or carved away to provide contrast or create a design. (Similar low temperature heating of ivory has been used, by unethical antique dealers, to darken its surface and create the illusion of great age). Low temperatures must be used on these gems as due to their organic nature, they will char, melt or burn!

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In its natural state, much amber is cloudy or milky, an effect caused by suspended air bubbles. (If you have ever seen "whipped" honey, the appearance is very similar). Heating such pieces in oil can clarify them to a great extent (solid inclusions, if present, will remain however). Finally, when amber is heated in oil and then "quenched"(plunged quickly into a cold liquid), characteristic stress fractures, that look like flat disks, form. These have been euphemistically called "sun spangles", and to some tastes, are an attractive enhancement. The brooch photo below shows clear and cloudy amber of a variety of colors. The carving illustrates the surface nature of the heated color (where some of it has been removed by the carving process), and the close up shows the "sun spangles" in a piece of amber jewelry.

[Amber brooch with a variety of heated and unheated amber cabs, heat treated amber carving, "sun spangle"stress fractures created by quenching heated amber]

Heating beryl: Two species of beryl gems are commonly heat treated. Aquamarine and Morganite occur naturally in shades of slightly greenish blue, and slightly yellowish pink, respectively, but the "market preferred" colors are pure shades of blues and pinks. Heat is used to obtain these preferred colors. (The temperatures necessary to accomplish the removal of yellow tones by changing one iron ion to another using a reducing atmosphere, are low, and therefore, generally leave no obvious signs.) Therefore, aqua and Morganite of pure blue or pink color should be assumed to have been heated, unless otherwise stated. The change is subtle and hard to capture with a camera, especially in Morganite as its color tone is so light, but the images below may give a general idea of the effect. 205

[Unheated and heated aquamarines]

[Unheated and heated Morganites: Morganite images, copyrighted, used with permission of http://www.mineralminers.com]

Heating chalcedony: Of the many forms of chalcedony, carnelian is the only one which is likely to be heated. The orangey brown color of carnelian comes from its iron oxide content, which, when unheated, is hydrated (chemically, it has loosely attached water molecules bound to it). This form of iron oxide is known as limonite and is yellow to orange to brown in color. The amount of limonite which stains the chalecdony will differ, making carnelian naturally highly variable in tone and hue. Heat removes the bound water from the limonite and converts it to the unhydrated form, hematite, which, as its name suggests, is blood red in color. Due to the low temperatures involved (the Ancients simply put it in the sun to bake) it is not possible to discriminate natural heating which might occur underground during, or after, gem formation, from that which is man-made. Therefore, if the color is significantly on the red side, assuming it to be heated, is erring on the side of caution.

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[Carnelian briolette beads showing variation in natural color due to variable limonite content, unheated carnelian cabochon, a pair of very red carnelian cabs, which should be assumed to be heated]

Heating corundum: Virtually all corundum gems (sapphires and rubies) have been heated. Many different outcomes from the heating processes are possible depending on the temperature, atmosphere, and the particular chemistry of the material being treated. Interestingly, in corundum, heat: 1) can either increase or decrease color intensity, 2) it can dissolve rutile to clarify a piece, or 3) exsolve it to create or emphasize chatoyance or asterism. 4) It can be used to partially heal fractures improving clarity, and 5) it can diminish the tell-tale appearance of "curved striae" in synthetics by paritally melting these layers into each other. We learned that heating can remove yellow tones in aqua, but by changing the conditions, it can emphasize them in sapphire. By using high heat and an oxidizing atmosphere, a pale yellow sapphire can acquire a deeper, richer color. Blue tones in corundum can be increased or decreased: which way it goes is controlled by altering heating and atmospheric conditions. High temperature and rapid cooling under reducing conditions can change the ions of iron and titanium in pale blue sapphires to a form which results in a stronger blue color, for example. On the other hand, some corundum suffers from too much blue color --> like certain quite purplish rubies and those "midnight" sapphires, so dark they virtually look black. Some of these gems are susceptible to conditions (oxidizing at high temperature) which removes some of the blue, making them much more attractive and saleable.

[Various color altering results of heat treating corundum gems: deepening yellow, deepening blue, lightening blue, removing blue, therefore correctlng purple to red] 207

Corundum is also heated to change its clarity status. This is accomplished in two ways. Rutile is a mineral which, depending on conditions under which the gem was formed, may be dissolved within the corundum, and therefore not visible to the eye, or may have crystallized within the corundum as discrete needles affecting clarity and the chatoyance phenomenon. "Silky" corundum can be heated and cooled under precise conditions which will cause the rutile needles to dissolve into the corundum thereby greatly clarifying the gem; or conversely, gems with significant dissolved rutile can be subjected to heat and temperature regimes which encourage the dissolved rutile to "exsolve" into solid needles. **Check the text: On pg. 94 of the Hall text there is a microphotograph of just the type of "silky" ruby that would benefit from dissolving its rutile needles -in this case they are too few for good star potential, so dissolving them would make for a more beautiful and valuable transparent stone. Due to the possibility of clarification, an increased percentage of potentially chatoyant corundum is now sold as transparent material, and the number of available star gems has decreased. Gems with significant fracturing that causes loss of transparency can be subjected to very high heat which, by melting the thin edges of the fractures causes partial healing and, therefore, clarification to occur.

[A ruby whose originally modest star potential was enhanced by controlled heating, a pair of once silky blue sapphires, clarified by heating] ** Check the web: This company's website shows their high tech corundum treatment furnace and a couple of cool before and after pictures: http://www.swdgems.com/HeatTreatment.html Evidence for heating in sapphires includes discoid stress fractures, singed (partially melted) surface facets, internal crystals with rounded, melted edges, and partially reabsorbed silk. Evidence against heating is shown by intact silk, highly angular included crystals, and lack of discoid fractures. 208

[Heated for sure: discoid fracture in sapphire: Image courtesy of Martin Fuller, proof of no high temperature heating: intact silk in a sapphire] Most corundum gems cannot be called either way, so it is prudent to assume heating, as it is so prevalent in the marketplace. **Check the web: Heating sapphires is SO common that even this company which calls itself "All Natural Sapphires" and boldy disclaims using gem enhancements can only go so far as to claim that "almost all of its sapphires are unheated". http://www.thenaturalsapphirecompany.com

Heating diamond: After diamonds have first been irradiated to green and blue green, they are often heated (a process termed "annealing") to further alter their color. Generally, such stones change to yellow or brown, but, rarely, some pieces with slightly different chemistry or crystallography, heat to highly desirable pink, purple or red colors. The brown diamonds shown below are examples of annealed stones. The second photo shows an irradiated blue stone before and after annealing. The annealing takes place at relatively low temperatures (well within the range of that produced by a jeweler's torch). Inadvertent cases of annealing have taken place when jewelers neglected to remove irradiated blue or green diamonds from their settings before repairs were made --> customers were not happy to find their diamonds had turned yellow or brown.

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[Diamonds that have been irradiated then heated to change their color, the brown stones were deliberately changed, the yellow one was an accident] A New Process to be Aware of: A new high pressure/high temperature process for color enhancing diamonds is beginning to impact the market. It uses the same equipment and conditions that are have long been used to synthesize diamonds, but the treatment time is far shorter than that used for synthesis. AGTA (Code = HP). Called HPHT for short, it can produce colorless, pink, and blue gems from some types of off-color rough or cut stones. Due to the very high temperatures used, only high clarity stones can be treated. Not all diamonds react to this treatment, but when they do the results are stunning and the value of the stone jumps significantly. About 5% of diamonds can be made colorless, and a larger percentage can be made into "fancies". The fancy colors, are more subdued and natural-looking than those produced by irradiation, and unlike the case with irradiated stones, there are no obvious signs to help identify them as enhanced, so laboratory analysis is required.

[HPHT "Press" used by Sundance, Inc. to color treat diamonds, an example of a "before and after" showing a dramatic improvement in color: Images courtesy of Sundance, Inc.] Although Sundance, Inc. is doing business honestly, and attempting to prevent fraudulent representation of its goods, you can see, I think, how tempted some might be to try to pass off these relatively inexpensive enhanced gems as the higher priced "real thing".

Heating quartz: As with corundum, heating quartz can have various effects. Gentle heating of dark or muddy amethyst lightens the purple, and 210

can reduce unattractive grey and smokey tones. At higher temperatures amethyst converts to yellow or orange citrine or, rarely, to yellow-green prasiolite. (Chemical or physical factors present in amethyst mined in only a few sites are of the sort that create prasiolite when heated, so it is much rarer than citrine. Citrine does occur naturally, in which case Nature has already supplied the heat, but in general, natural color stones are notably lighter in tone than those produced with human help. Smokey quartz when heated can turn yellow, also making citrine although this is less commonly done than heating amethyst. Tiger'seye which is usually a golden yellow color will become red upon heating.

[Various outcomes of heating amethyst: lightened amethyst, citrine, prasiolite]

[Unenhanced citrine]

[Heated quartzes: citrine from heated smokey quartz, enhanced red tiger'seye]

Heating topaz: Two types of topaz are routinely heated. 1) White topaz, as a first step in its color enhancement, is irradiated to brown, and it must then be heated to create a stable blue color. 2) Much natural ("precious") topaz of a yellow or orange color, some with subtle pink overtones, is unattractively muddied with brown, which can usually be removed or reduced by heating, a process traditionally referred to as "pinking". As can be seen in the photo of the four stones on the right below, the results are variable. 211

Both processes use relatively low temperatures, so there is little evidence left behind. Once again, it is prudent to assume that any blue or precious topaz has been heated unless it can be proven otherwise. Natural blue topaz is very rare, and when found it is generally quite pale, and pinking of precious topaz rough is standard practice virtually everywhere that it is mined.

[Heated (sky, Swiss and London blue topazes): blues are heated postirradiation, "pinked" precious topaz]

Heating tourmaline: Heating can be useful in lightening the color of some dark blue and green tourmalines that without such treatment, look almost black. Unfortunately, not all dark stones respond to the heating. In some cases, as with amethyst, muddy tones also can be lightened or removed. For these reasons, the majority of blue and green tourmaline rough is heated, so it is prudent to assume it. Some red tourmalines (rubellites) can be improved in color by heating, and though not common practice, it is occasionally done.

[Heated blue and green tourmalines, lightened enough to be attractive, a red tourmaline that might possibly have been heated] As with topaz, the temperature used for tourmaline is fairly low, so there are few telltale heat-altered inclusions to leave evidence of it. Such stones, however, can be more brittle than unheated ones which can sometimes be deduced by noticing facet junctions that are abraded more easily than the norm.

Heating zircon: Zircon which occurs naturally in orangey brown shades, has both a long history of use as a gem, and a long and creative history of enhancement by heating. 212

** Check the text: Page 73 of the Hall text has a very nice picture of a step cut rectangular unheated stone that shows the natural color very well. The same stones are sometimes put through a series of heat/atmospheric enhancement regimens in an attempt to induce a change to a more desirable color such as blue, blue-green, red, yellow, orange, or red. Individual stones (based on their own unique chemistry) react in various ways. The description that follows applies to the majority of zircon gems: In the first step of treatment, rough zircon is exposed to temperatures of around 1000 degrees C, in a reducing atmosphere where many brown stones turn blue, some turn white and others don't change.

[1st Round: before, brown, and after: blue or white] Those which do not respond may then be re-treated at slightly lower temperatures of about 900 degrees C, in an oxidizing environment. Results can vary from yellow to white to red.

[2nd Round: before: brown stones which didn't respond to initial heating, after: yellow, white, or rarely, red] Stones may sometimes go through several cycles of heating, and can get rather brittle, which may make facet edges susceptible to abrasion. Although shades of orange, red and yellow are occasionally found in Nature, white and blue occur so rarely that heating must be assumed for these colors.

Heating zoisite: When a transparent variety of zoisite was first found in Tanzania, Africa, there was little excitement due to its dull, brownish yellow color. Experiments with heating, though, soon yielded gems of a beautiful 213

blue-violet color. As it turns out, heating was turning one of the color axes of this naturally trichroic gem from yellow-green to colorless, and allowing the less dominant blue and violet colors to be clearly seen. "Tanzanite" was born. As is so commonly true of gem rough, some individual pieces have atypical chemistry or crystallography, and react differently to treatment than most. In the case of this type of zoisite a very small percentage of the gems heat to an attractive green to blue green color. Dubbed "Green Tanzanite" (a misnomer, but one that stuck), such specimens have high value as collector stones, and are quite beautiful in their own right.

[Typical unheated color of Tanzanian zoisite, the usual blue-violet result of heating, the rare green result]

Help! I want my gems unheated! There are two major groups of gems that aren't heated: 1) heat sensitive gems like opal, apatite, pearls, and turquoise, and 2) those for which heating makes no improvement, or isn't economical such as garnet, spinel, chrysoberyl, iolite, peridot, sunstone, moonstone, jade, and most collector stones. If unheated is what you want, that is fine, but outside of the groups listed, you can expect to pay a premium for unheated goods, and some types of gems like blue zircon and Tanzanite will be off limits entirely. Another point to keep in mind is that "unheated" doesn't mean the same thing as "unenhanced", although there are those who can profit from implying it does! I have seen several dealers on independent websites, online auctions, and at gem shows that proudly advertise their wares as "unheated" when their goods have been, dyed, coated, irradiated, oiled or in some other way enhanced. Naive buyers can be deluded into thinking they've purchased an unenhanced stone.

Irradiation: ( AGTA Code = R) After heating, the most commonly used treatment for gem enhancement is irradiation. With some important exceptions (like diamonds), treated stones are usually not distinguishable 214

from untreated ones, as gems are often subject to similar, but natural, irradiaton effects during, and after, their formation. A variety of sources of, and processes for, irradiation have been tried, some, proving unsatisfactory, have been abandoned, others are still in use. The earliest experiments with irradiating gems used alpha particles (helium nucleii) which worked as desired, but left the gems with strong and highly persistent residual radiation. Today, beta particles (electrons) generated in linear accelerators, neutrons from nuclear reactors, and gamma rays usually from radioactive cobalt sources are used. Although the bombardment with neutrons and, to a greater extent, with electrons, can leave some residual radioactivity, its duration is relatively short. Government agencies in the USA, and other gem irradiating nations, have strict regulations for the holding and testing of irradiated gems to assure that they are not released to the public until they are safe to handle and wear. As we saw to be the case with heating, different types and durations of irradiation produce different results. Combining this fact with the idea of individual variation in gem chemistry, and that irradiation may or may not be followed by some sort of heating process, and we can begin to appreciate the tremendous diversity of possible results.

Irradiating beryl: Colorless beryl (variety = Goshenite) can be irradiated to stable shades of yellow to gold (variety = golden beryl or heliodor). Unenhanced golden beryl is also common, and it is essentially impossible, outside of a large gemological laboratory, to tell whether it was man or Nature that supplied the color producing irradiation.

[Goshenite, golden beryl] A boondoggle perpetrated on the gem buying public several decades ago, is still remembered by some wary dealers and buyers. Some beryls, with an unusual chemistry, turned a vivid and attractive blue when irradiated. They were rushed into the market with much fanfare under the tradename "Maxixe" beryls. The fly in the ointment was that these stones 215

were unstable in light, and reverted to their intially colorless state relatively quickly under normal use conditions. There would be little point in bringing up this unsavory memory, except that in 2003 explorers in Canada unearthed a bright blue deposit of beryl reminiscent of the Maxixe color. This material is colored by iron (not irradiation), and the color is stable. As of yet, the mining efforts have not yielded any facet quality rough, but exploration is proceeding. The only known deposit is presently owned by "True North Gems" and their material, already popular with collectors, has been christened "True-Blue Beryl".

[Unstable irradiated "Maxixe" beryl, natural color, stable, "True-Blue Beryl": Image courtesy of True North Gems]

Irradiating diamonds: As presented in the section on heating gems, diamonds irradiate to green or blue green. Another color which is commonly produced via irradiation is "black". Well, actually, it is not black but a very, very, dark green, and the visual impression is definitely black. Diamonds do occur naturally in black (if they are highly included), but irradiated "black" diamonds, when subjected to very concentrated light source, like a fiber optic light, show green color at the extreme edges where the girdle or facets are thinnest, whereas this is not true of unenhanced black diamonds. Virtually all the black diamonds used in jewerly today are the irradiated type.

[Typical blue-green color of many irradiated diamonds, very dark green "black" irradiated rose cut diamond]

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You will recall that these irradiated stones can then be annealed (heated) to brown, yellow or, less often, some of the rarer fancy colors like red. These heated and/or irradiated colored diamonds tend to have more vivid (some might even say "garish") colors than naturally colored fancies. Unlike what is seen with the majority of species which are irradiated, the process does tend to leave tell-tale signs in most diamonds. Patterns of color zoning that show up microscopically, with certain lighting conditions, can usually give the trained observer evidence of the treatment. With enhanced blue colored diamonds, though, there is a definitive test--> electroconductivity. Diamonds that come by their blue color naturally contain boron impurities which allow them to conduct electricity, irradiated blues get their color by the effect of irradiation on their crystal structure, and like all other diamonds, don't conduct.

Irradiating pearls: One of the many possible enhancement processes that are used to change color in cultured pearls, the use of gamma irradiation has different effects on fresh and saltwater cultured pearls. When saltwater pearls, like Akoyas, are irradiated, it turns the bead nucleus (made of shell) dark, which then shows through the unaffected translucent nacre layer making the pearl look grey or perhaps grey-blue. In the case of cultured freshwater pearls, the irradiation actually affects the nacre layers creating silver, gold, black and even multi-hued, often intensely metallic looking colors. (This difference is due to the slightly different trace element chemistry of nacre produced in fresh vs saltwater.) The treatment in both cases is stable. With saltwater pearls it is usually possible to get a magnified view down a drill hole which will reveal the darkened bead nucleus. Identifying irradiated freshwater cultured pearls (which usually have no bead nucleus) can be as simple as becoming familiar with the natural color range of these gems. Once that is accomplished, the completely unnatural looking irradiated stones jump out at you and identify themselves!

[Irradiated freshwater cultured pearls: Image courtesy of www.earthstone.com] 217

**Check the web: This GIA report was done shortly after the 9-11 incident. At the time, some letters and parcels were being irradiated by the US Postal Service as a counter bio-terrorism measure. The before and after pictures show how sensitive pearls are, even to low levels of radiation:http://www.gia.edu/newsroom/608/384/news_release_details.cfm

Irradiating quartz: Colorless quartz, rock crystal, is irradiated to produce smokey quartz in shades from light to very dark brown or greybrown. The smokey quartz found before modern irradiation techniques were developed, and a proportion of that mined and sold today, comes preirradiated by Mother Nature. A relatively recent discovery of a unique type of rock crystal at a particular series of mines in Brazil gives quite different results when irradiated. The resulting material known variously as "neon" "lemon" and "oro verde" quartz has a highly saturated, slightly greenish yellow color. Due to its striking color and its availability in inexpensive, large, clean pieces, it has become the recent darling of carvers, concave facetors and fantasy cutters, as well as a staple of the home shopping channels, and internet gem auctions. Once again, with smokey quartz, we have a case where it is difficult to impossible to determine the origin of its color, and it is best to assume it has been irradiated by man, in the absence of proof to the contrary. Not so, with the yellow material, as its only known source is from the irradiator's factory.

[Rock crystal quartz, smokey quartz (could be natural color or irradiated), "oro verde" quartz (always irradiated)]

Irradiating scapolite and spodumene: Although these two gem species are likely to be unfamiliar outside of gem circles, they provide some interesting examples of the effects of irradiation. Scapolite is found naturally in light to medium shades of yellow, and also in pale lavender. The yellow

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material can be irradiated to a much deeper, and more brownish, shade of lavender than that which occurs naturally. Spodumene occurs naturally in colorless, light to medium pink/lavender (Kunzite), and very rarely in a chromium colored, grass to emerald green stable variety known as Hiddenite. Kunzite can be irradiated to a light to medium green color which is often given the misnomer of Hiddenite, and sold for inflated prices to naive collectors. Not only is the irradiated material not Hiddenite, as its color does not come from chromium, but it fades quite noticeably in the light, a fact too rarely included in the sales pitch. **Check the web: This web page from the North Carolina Museum of Sciences, shows and discusses the very rare gem Hiddenite with a photo of the original specimen collected by William Hidden in 1905:http://www.naturalsciences.org/funstuff/notebook/geology/hiddenite.html

[Yellow scapolite, irradiated purple scapolite, Kunzite (pink spodumene), irradiated green spodumene: image courtesy of www.faceters.com]

Irradiating tourmaline: The world's supply of attractively colored pink to red tourmaline has recently been greatly increased by new discoveries. Some Brazilian tourmalines, formerly rejected due to poor color, and the majority of the large new deposits being found in Africa, are irradiated to diminish brownish tones. The permanent improvement in appearance (alas, not all pieces are susceptible) is similar to that displayed in the two stones below:

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[Typical "before and after" colors of some low grade tourmaline that is susceptible to drastic improvement in color after irradiation ]

Irradiating topaz: In terms of sheer carat weight, and probably also in terms of economic value, blue topaz is the most important irradiated gem. Colorless topaz is plentiful and inexpensive, but not all of it will irradiate successfully. Treaters generally screen the rough with an inexpensive gamma ray treatment which identifies the rough which will benefit from further irradiation, before proceeding with more costly and time consuming treatments. These "good candidates" then go to either a linear accelerator to be bombarded with electrons, or to a nuclear reactor to be exposed to neutrons. Depending on the duration and type of irradiation, and the sort of heating process used afterward, the results vary from sky, to Swiss to London blue. Other slight color variations have been produced and given their own tradenames like "electric blue" and "neon blue". London blue is the scarcest and most expensive type because it requires neutron exposure (most expensive process), and the longest holding times. Now that so many other types of gem materials are being irradiated, topaz treaters are having to pay more to "book" accelerator or reactor time, and prices for these once quiet inexpensive gems have correspondingly risen. With most gem materials, much, if not most, of the cost of the finished gem, is associated with the gem rough itself. Blue topaz is an interesting exception to this, as the rough is the least expensive part, with fashioning, and even more so, treatment, responsible for the bulk of the costs. The irradiated colors are stable, and the gems are perfectly safe to wear, but the dual heat/irradiation processing does leave them somewhat more brittle than unirradiated stones. Added to the natural tendency for cleavage, this makes blue topaz one of those gems which, despite its hardness of 8, is not a good choice for daily wear rings or bracelets.

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[Unenhanced white topaz, sky blue, Swiss blue, and London blue irradiated/heated topazes]

Unintended Consequences! The introduction of huge amounts of blue topaz into the market place in the last several decades has had some interesting side effects on other gemstones. 1) For a time, it depressed the prices of aquamarine, as sky blue topaz made a pretty good aqua simulant at about 1/10th the price. With time, though, most aquamarine lovers went back to their original gem choice, with the ironic twist of a noticeable decrease in the traditional preference for heated "pure blue" stones. More and more aqua fanciers are now seeking out the greenish blue unheated stones--> possibly because these are less likely to be mistaken for the ubiquitous and inexpensive blue topaz! 2) The other effect has been to literally wipe out the identification of the word topaz with the color yellow. Yellow, or precious topaz, was, until the advent of irradiated blue, the most common and familiar type, and is still the traditional birthstone for the month of November.

[For centuries, these were the colors that the word "topaz"evoked!] Food for thought: (Answers to the questions are found at the end of the lesson) Question 1: Your friend wants an untreated gemstone and has found a dealer with some beautiful golden beryls. The dealer assures him that they have not been heated. He asks for your advice. What do you tell him? 221

Waxing: (AGTA Code = W) When the surface of a gem is coated with colorless wax, (or oil) the process is termed waxing. Generally, this treatment is used with stones with a vulnerable, porous surface, or those with microscopic surface imperfections whose polish luster can be boosted with it. Porous materials like turquoise that have been waxed, are thereby, at least partially, protected from absorbing skin oils and other environmental contaminants. Although, not permanent, the gem community tends to adopt an extremely forgiving attitude toward this treatment, as it is both a very long standing tradition, and a simple matter to re-wax the gem. (Paraffin and beeswax are the traditional materials used, and re-doing a gem can be as simple as painting on melted wax and buffing off the excess). Most of the world's highest grades of turquoise and jadeite can be assumed to have been given this treatment. It is also occasionally used with lapis lazuli, rhodocrosite, serpentine, variscite and Amazonite.

[Persian grade, waxed turquoise earrings, waxed "A" jadeite, moss-in-snow cabochon, waxed lavender "A" jadeite ring: Image courtesy of Mason-Kay, Company]

Dyeing: (AGTA Code = D) Dyeing is relatively easily accomplished with porous gems and those crystalline gems which are aggregates. The pores and the spaces between the microcrystals allow the dye to be taken up. Single crystal gems, however, arenot good candidates for dyeing as they will only take up dye where they have surface reaching fractures. There is really only one case in which dyeing is an "accepted industry standard", and has no effect on the value of the gem: black onyx. All other instances of dyeing (when disclosed) negatively affect the value of the gem, in some cases, dramatically. Examples of porous and aggregate gems which are frequently dyed are chalcedony, jade, coral, pearls, and howlite.

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There are some cases where the absorption spectrum of a gem can identify specimens which are dyed, but they are rare. The usual ways of detecting dyed gems are: 1) By microscopic examination: looking at pores, bead drill holes, and surface fractures for dye accumulations. 2) Testing with a solvent, a destructive test, yes, but one which can usually be done in an inconspicuous area. Useful solvents are acetone and denatured alcohol, but not all dyes are soluble in them, so a negative test in not conclusive. 3) Comparison to the normal range of gem colors and evaluation of the avialability and cost --> naturally colored chalcedony in unknown in hot pink for example, and Nature doesn't yield neon green pearls. Saturated, medium dark, lavender natural color jade is worth a King's ransom, so pieces of that color seen on ebay for $10 are very likely to be dyed. (Compare the color of the inexpensive jade beads below with the picture of the very expensive natural color lavender jade ring above).

[Dyed "C" jadeite green earrings, and lavender beads: image courtesy of www.mbbeads.com, a microscopic view of dye accumulations in jadeite: image courtesy of Martin Fuller]

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[Dyed coral beads, dyed freshwater cultured pearls: image courtesy of www.mbbeads.com]

[Typical natural color of chalcedony, typical non-natural color achieved by dyeing] One of the most commonly dyed materials in today's marketplace is howlite, an inexpensive, porous, white mineral that generally has grey to black veining. It has been used to simulate turquoise, lapis, rhodonite, and other opaque gems. The dye penetrates only a short distance into the gem, so scratches and chips are revealing, but when undisturbed, a piece can be quite convincing.

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[Howlite in its natural color: image courtesy of Bill Wise, dyed to imitate lapis lazuli: image courtesy of www.earthstones.com, dyed to imitate a turquoise nugget, the nugget sawn apart to reveal the undyed interior] When single crystal gems are dyed, they must be fractured first. In order to achieve this, the age old method is "quench crackling". Generally this is done by heating the gem, and plunging it in cold water, but strong ultrasonic vibrations have been used to accomplish the same thing. Dye can then be absorbed into the fractures which, when numerous enough, give the piece an overall color.

[Two pieces of quench crackled, dyed rock crystal quartz, the pink one has been magnified and shows clearly that the dye is only in the fractures] In the great majority of cases, the dye is a chemical or pigment of either natural or synthetic origin. An example is the use of silver nitrate, a chemical that darkens on exposure to light, which has been used on pearls for many years. There are a couple interesting cases, however, which involve "carbonization". Chief among these is the production of "black onyx". Here's one of those cases where a misnomer continues in use, just because of familiarity and convenience. (Onyx by definition is has color bands, so a solid black material just doesn't qualify). There are very small amounts of black chalcedony found in Nature, but the virtually all of that in commerce is carbonized chalcedony. Colorless to light grey chalcedony is soaked in a sugar solution until its internal pores are filled with it, then it is boiled in sulfuric acid which "carbonizes" the sugar turning it black. There are now microscopic sized 225

black specks throughout the piece, giving it a uniform and stable black color. When I was first learning about gems, I just couldn't believe that this primitive method, developed hundreds of years ago, was still the major mode of production...but it is!

["Black onyx" ring, technically "carbonized chalcedony"] **Check the web: Here's a web page with a quite detailed "recipe" for making black onyxhttp://www.ganoksin.com/borisat/nenam/black-dying-agate.htm A similar process is used to color certain matrix opals (particularly those from Australia's Andamooka region), whose matrix is a light color, giving little contrast to the patches of color of the opal within the matrix. The result of the darkening of the matrix is an improvement in contrast and therefore in the appearance of the color play.

Bleaching: (AGTA Code = B) Probably the most routinely bleached gem, is pearl. Historically, long before cultured pearls were invented in the early 20th century, pearl fisherman would spread their treasures out in the bright sunshine, carefully rotating them over a period of time, which tended to lighten and even the color, and diminish some unsightly dark spots. Light is still used in some pearl processing facilities. (Anyone whose hair gets lighter in with long exposure to sunshine, or whose window drapes have faded over time, will realize how effective a bleach light can be. Besides its use in removing blemishes and evening out color, bleaching is a tremendous aid to manufacturers in matching pearl colors. Today's pearl consumer demands that each and every pearl in a strand, is exactly the same shade---> Mother Nature prefers to make a wide variety of shades, even within the same species of oyster or mussel, living in the same body of water. In addition to light, chemicals such as hydrogen peroxide (Lady Clairol, anyone?) and chlorine (as in Clorox bleach), speed up the process, but on delicate organic gems like pearl and coral, must be used at low strength and with care.

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[Large scale bleaching of pearls with chemicals and/or under lights: Images courtesy of www.man-sang.com] Golden coral is rare and valuable, so is black coral. Depending on the ups and downs of the market, the vagaries of supply, and prevailing public tastes, there are times when black coral is bleached to gold (peroxide is used).

[Bleached black coral beads: Image courtesy of www.stonesnsilver.com] Jade is another frequently "bleached" gem, but in this case strong acids are used which really aren't bleaching the color to a lighter shade, they are literally dissolving away discoloring inclusions. Such bleached jade requires further treatment to seal the cavities formed by bleaching. (See below.) Acid bleaching is also used in conjunction with laser drilling in diamonds to remove "carbon" spots and other discolorations. The laser creates a narrow channel by which the acid can penetrate the interior of the diamond and do its work. As with jade, this process is generally followed by one which "fills" the cavity. (Again, see below)

Impregnation (aka "stabilization"): (AGTA Code = I) When a colorless, hardened, resin is suffused throughout a porous stone to make it more durable or improve its appearance, it has been impregnated. A 227

common market term for such gems is "stabilized". There is only one imporant type of gem for which this treatment is essential--> without impregnation, ammolite is too fragile to withstand fashioning or wear. Unenhanced specimens, exist, but are suitable only for display. Other gems like jade or turquoise are commonly treated in this manner. Low grades of highly porous turquoise that may have nice color, but are excessively fragile, or near impossible to polish, can be greatly improved by resin impregnation. "B" and "C" jades, after being acid bleached have resin infused into the resulting cavities (if the resin is colored, then the piece is considered dyed, "C" jade).

[Impregnated gems: ammolite pair, turquoise cabochon, "B" jade ring]

Oiling: (AGTA Code = O) and Filling: (AGTA Code = F) Both of these types of treatments involve the filling of surface reaching fractures or cavities with colorless oils, resins, or glass. They are done for the same reason: to clarify a gem, bydecreasing the relief of the fracture or cavity. The difference between them hinges on whether the filling material is essentially a liquid (oil or unhardened resin) or solid (hardened resin or glass). Of the two, oiled gems are more accepted in the gem marketplace and do not depress value greatly. Even though the oil treatment is temporary, the favorable viewpoint comes both from the long standing and widespread use of gem oils, and the fact that it can be successfully be re-done if necessary. Virtually all emeralds are oiled, some as rough at the mine site, others only after they are cut. Certified unoiled emeralds bring a 10% - 20% price premium. If the oil is colored, then the emerald is considered to be dyed, and its price is much more severely affected.

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[Emeralds: routinely oiled to improve clarity] Filled gems are another matter. Although it can be argued that the filling, being hardened, is less likely to evaporate or be dislodged by cleaning and wear, several factors create a generally negative impression that translates to a drastic effect on gem prices. The solid resins can discolor and become more opaque with age, and since they cannot be removed, will then permanently degrade the gem's appearance. Fairly large areas can be filled with solids, which are less durable than the host gem and can become scratched, chipped or dulled with wear. This process is primarily used with rubies and diamonds, both very valuable gems, so it must not be forgotten that these chunks of glass or plastic resin are adding weight to the gem. That is, adding weight of a material which is not valuable, but which the customer is paying for. Until just recently, diamonds were the only major gem for which glass filling was a concern. Now, however, the number of glass filled rubies in the marketplace has risen to the point where gem professionals and alert buyers need be wary. Glass or plastic filled gems are worth only a small fraction of the value of their unenhanced equivalents. Fortunately, there are several ways to detect glass or plastic areas in gems. Under reflected light, the luster difference between a ruby or diamond, and its glass filler are easy for the trained observer to spot. Some fillers fluoresce and give themselves away. For those which are confined to thin fractures, the "flash effect" is a tell-tale sign. The Flash Effect: As a gem is rocked and tilted under appropriate lighting and magnification, these thin filled areas will first flash one solid color like orange and then, at a different angle, a different color like purple. Novices may confuse this with the cleavage rainbow seen in unfilled fractures, but in the flash effect, only one color is seen at a time.

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[Fracture filled diamonds showing the "flash effect": Images courtesy of Martin Fuller] Gems which are properly disclosed as oiled or filled, should include appropriate care instructions. For example, oiled emeralds should not be steam or ultrasonically cleaned. Jewelry containing filled rubies and diamonds should not be repaired or resized without removing the gems from the settings, as heat from a torch or immersion in metal cleaning solutions can cause melting or etching of the filler. Food for thought: Question 2: You walk into a jewelry store with your brand new gift ruby ring, and the emerald brooch you inherited from Aunt Minnie. You want the ring sized, and a new closure soldered onto the brooch. You ask the jeweler for the estimated charges including dismounting and remounting the gems. She says dismounting will not be necessary. What should you do?

Laser drilling: (AGTA Code = L) Thus far, this treatment, a type of clarity enhancement, has been seen only in diamonds, and is virtually always combined with acid "bleaching" and fracture filling. The purpose of the tunnel created by the laser is to provide a channel for the acid and glass, or resin, to enter. The entry points are tiny, as seen in first photo (red arrows) and can be easily overlooked, but microscopic examination (usually 10x is sufficient) makes this treatment one that can be positively identified.

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[Laser drilled diamond, surface view and magnified view: Images courtesy of Joe Mirsky, laser drilled diamond, note flash effect being shown by filled fracture at the base of the laser tunnel: Image courtesy of Martin Fuller]

Diffusion: (AGTA Code = U) When gems are diffused, they are heated to very high temperatures, just to the verge of their melting points. This heating is done in the presence of a material which contains chromophores such as titanium, chromium or other atoms, which are then able to diffuse into the stone's surface or interior to change color or create phenomena. Two such processes are currently in use: 1) surface diffusion, and 2) bulk or "lattice" diffusion. Surface diffusion has been around for decades and, until recently, was pretty much confined to use on blue sapphires and the occasional ruby. By packing already faceted, light colored stones into a container with powdered titanium and iron, and heating to very high temperatures, a thin surface layer rich in these chromophore elements is formed, which through selective absorption, greatly darkened the apparent blue color. Such stones must always be repolished afterward as the high heat tends to mar the surface. In the repolishing process it is inevitable that some of the thin layer is unevenly removed, so that when viewed under immersion and/or in diffused light, an uneven pattern of color--> paler on some facets than others and darkest at the edges of the facets, can be seen. If the diffused stone has inclusions at all, these will also show the typical signs of high heat, such as partially resorption of silk, partial melting of crystals, or stress fractures. With such obvious signs of treatment, only the unschooled or unwary buyer is likely to be duped.

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Below is a picture of a 1.53 ct. sapphire. A beautiful stone: top color, eyeclean, and reasonably well cut. In today's market one might expect to pay between $1000 and $1500 per carat, retail, or even more in an upscale jewelry store for a sapphire with this kind of appearance. This stone's actual retail price was $150 for the piece, or less than $100 per carat. What a bargain, you say --> and why so cheap? (No, it is not a synthetic!)

[An attractive, color enhanced, natural sapphire] The price paid, was, however, appropriate to the stone. It is a natural origin sapphire, but it is has been color enhanced by surface diffusion. The lovely color layer has a thickness of much less than one millimeter, the rest of the stone is either colorless or an unappealing pale blue or grey. Such stones represent a bargain, as long as the customer understands the limitations inherent to them. Any scratch, chip or nick will remove the color layer revealing a light spot, and the stone cannot be recut or it would lose its color entirely. As a stone to be used in a pendant or earrings or even a ring worn once in a while, it will look beautiful for many years, but it is not an appropriate choice for a frequently worn ring or bracelet. You can see from the photo, that looking at the stone in ordinary light doesn't tell you the source of its color. Below are two 10x magnified photos of this same gem, (you can do this kind of observation with your loupe, no fancy microscope is necessary). In the first, the gem is seen in diffused light, in the second, it is immersed in water and viewed with diffused light. Both photos give unequivocal evidence of surface diffusion. Look closely and note the color differences from facet to facet (natural color zoning does not follow facet shapes), especially telling is the way the color is darker along the keel and at many of the facet boundaries.

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[Magnified views of a surface diffused blue sapphire: under diffused light, under immersion in water with diffused light]

Making Stars When titanium dioxide (rutile) is surface diffused into a sapphire, and the heating and cooling is controlled so that it exsolves into needles, asterism is created in the stone. Again, you are looking, in the photo below, at a natural sapphire, but one that has been surface diffused with rutile. Such gems are very inexpensive compared to unenhanced, natural star sapphires. In comparison to an unenhanced star stone, the star figure is stronger, more even, and seems less mobile as the light source shifts direction.

[A surface diffused star sapphire] A recent entry into the world of surface diffused gems is topaz, now available in bright colors such as green and red as well as bi-colors. The advertisement below is from an ethical company (RioGrande), which is one of the major suppliers of gems to jewelers: notice the enhancement code (U) and the appropriate warning about recutting.

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[Graphic courtesy of RioGrande Corp.] In 2004 Leslie and Company introduced the first surface diffused bi-colored topazes to complement their existing line of tradenamed diffused topaz gems.

[Surface diffused topazes: Images courtesy of Leslie and Company] Bulk or lattice diffusion was discovered to be occuring in 2003 when stones that began appearing the market in 2002 were critically examined. The gems were sapphires of an extremely rare and valuable color called "padparashah" (orangey pink). The inexplicably large numbers of fine colored stones suddenly available, raised questions that led to a fervor of activity among the staff gemologists in organizations such as AGTA and GIA. Athough the treaters were freely acknowledging that the gems had been heated, they insisted that that was the end of the story. Adding to the 234

confusion, the stones did not fit the profile of diffused gems as the color penetrated well into the interior--> in many causes completely throughout the stone. Suffice it to say that they were finally demonstrated to be the result of a new diffusion process using the light element beryllium (Atomic number = 4) as colorant. With its small atoms, the beryllium chromophore was able to diffuse much further into the heated stones than titanium or chromium with their much larger atoms. The source stones were primarily light pink African sapphires which were then being were treated in Thailand.

[Bulk diffused "padparashah" sapphires] The "pre-discovery" prices were extremely reasonable for naturally colored, or simple heat treated paparashahs, but outrageously inflated for diffused goods. In the interim between the time the stones were stealthily introduced into the market, and the time their true nature was understood, quite a few greedy collectors and dealers re-learned the old lesson "If it seems too good to be true, it probably is". Viewed under diffused light and /or immersion, most of these gems show normal color patterns. Although they do have inclusions typical of high heat, positive identification of a particular gem as being beryllium diffused, requires the services of a large gemological laboratory. Although they are considerably more durable than surface diffused stones, recutting could still be a risky proposition, especially on larger stones.

Coating: (AGTA Code = C) Coated gems are those that have been treated with surface enhancements such as laquering, inking, painting, foiling, or sputtering of a film to enhance color, improve appearance or add phenomena. Coating has a long history: from use of gold foils in antiquity, to the painted back Rhinestones of the 19th century, to today's iridescent metallic coatings. 235

Coatings are usually fairly easy to detect, but can escape notice if they are applied only to back of the gem (as in a "foilback") and the gem's setting is fully closed. The coatings of foilbacks range from crude and obvious, to sophisticated and well hidden, as seen below.

[Contemporary "gumball machine" quality foilback ring (glass with metallic paint), circa 1910 high quality Rhinestone brooch (glass with metallic paint)] Perhaps the most nefarious of the fraudulent uses of coating is an old (but still in use) trick of putting a tiny drop of indelible blue ink or paint underneath the prongs holding an off-color diamond in its setting. The prong hides this dot of color from all but the most experienced eyes. The effect of the light reflecting off those blue areas and mixing with the generally yellowish light emerging from the gem, makes the yellowish stone appear shades whiter. (As an example, this technique might raise a stone's apparent color grade from M to F allowing the seller to make an undeserved profit.) The most common coatings in today's gem market are the metallic vapor films that create iridescent gems.

[Metallic vapor coated iridescent quartz ("aqua aura"), magnified view of metallic vapor coated "mystic topaz"]

Care of Enhanced Gems There are no overall rules, as some enhancements increase durability, while others decrease it. But these general precautions will protect almost any enhanced gem: avoidance of solvents, ultrasonic and steam cleaning, gentle 236

wear, protective settings, avoidance of recutting, and removal of gems from their settings prior to jewelry repair. Answers to the thought exercises for this lesson. (If you don't understand something in these answers it's time to email me and ask!) 1): You might make sure that your friend understands the difference between "unheated" and "unenhanced." Most likely he is under the impression that they mean the same thing. Few people who have not studied gems realize the vast number of treatment possibilities there are. You could also mention that a lot of the golden beryl in the market has been irradiated. A possible suggestion would be that he ask the dealer, point blank, whether the gem has had any enhancement at all. (On the other hand you might like to just keep your mouth shut, and smile, and agree that they are lovely). 2): The safest thing to do would be to walk right out and find another jeweler. The new ruby ring could be glass filled, the emeralds are almost certainly oiled--> in either case the heat from the jeweler's torch (even when methods are used to keep the gems isolated from the heat) can do major damage. Even if the gems were completely unenhanced, there is still the possibility of damage from inclusions due to thermal expansion. You have now completed the web lecture for the eighth lesson! Go back the the course website to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Nine: Synthetics and Simulants

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LESSON 9: SYNTHETICS AND SIMULANTS

Synthetics Synthetics are man-made gem products. The Federal Trade Commission is quite specific in forbidding the use of the term "gem" or "gemstone" (or any recognized species or variety thereof), unless that product is solely and exclusively the work of Nature. All other products offered for sale must be clearly identified with a readily understood adjective that indicates their synthetic status. Acceptable terminology for synthetics is variable, but would include product labels similar to the following: "synthetic gemstone", "laboratory-grown ruby", "cultured pearl", "created emerald", "manmade sapphire", "reconstituted turquoise". Synthetics can be exact copies of natural gems, or they can be unique materials which are not found in Nature. 1) Examples of the former include the synthetic rubies and emeralds. Such creations have virtually the same optical, chemical and physical properties as their natural counterparts.

[Synthetic, Chatham brand, emerald crystal cluster set as a pendant] (Also placed in this category are those created materials which are accurate copies of natural gems, except that they are produced incolors not found in Nature. Examples would be blue quartz, and white spinel-->except for color, these give all the same test results as the natural versions of that gem.)

[Synthetic blue quartz: quartz, yes, but in a color not found in Nature] 238

2) Man-made wholly "artificial" gemstones with no natural counterparts at all, include cubic zirconia (CZ) and YAG (yttrium aluminum garnet).

[YAG, a popular synthetic widely used in industry and as a gem, can be made in a variety of colors from white to pink to green, and has no analog in Nature] Check the text: See page 354 in the Lyman book for a picture and description of another artificial garnet GGG (Gadolinium Gallium Garnet) History Unlike enhancements and fakes, synthetic gems are a relatively modern development. Although there were some successful laboratory experiments earlier, the economically viable commercial production of a synthetic gemstone began with synthetic ruby produced in France in 1902 by Auguste Verneuil. By 1907 production was 5 million carats per year. The fact that synthetic gems were produced so early often comes as an unpleasant surprise to those who inherit or purchase a vintage jewelry item. The heir, or buyer, is expecting that the age of the piece, alone, guarantees natural origin. Although in more recent years synthetics are, at best, found in "entry level" jewelry, in the first two or three decades of the 20th century, synthetics were sometimes used by noted designers, and high end jewelers, who appreciated them as signs of "scientific progress" or "modernity".

[Circa 1910 gold, natural pearl and synthetic ruby ring] Why make synthetics? Outside their use as synthetic or simulant gems, physicists and chemists make large quantities of both copies of natural gems, and totally artificial ones, for industrial and research purposes.

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At present over 90% of the diamond abrasives ("bort") for industry, used in everything from the saws that cut through pavement, to dentists' drills, are synthetics produced in a laboratory. Laser and electronic technologies depend strongly on the properties of laboratory created crystals. Even a cheapie "quartz" watch has, at its heart, a synthetic quartz crystal. Lasers based on synthetic crystals are used in medicine in a wide variety of ways from surgery to removing tattoos to improving vision.

[Magnified picture of synthetic diamond crystals used as abrasives: Image courtesy of Dr. Jill Banfield] Beyond these practical applications, laboratory study and production of synthetic mineral crystals allows scientists to test hypotheses, and extend knowledge in many areas of the physical sciences. **Check the web: This company produces a variety of synthetic mineral crystals for laser and optical use: http://www.enlight-tech.com/crystalsYAG.shtml Crystal Formation Processes Both in Nature, and in the laboratory, there are three basic ways in which crystals form. 1) Melt (a molten material solidifies) 2) Solution (a solid is precipitated from a liquid in which it was dissolved) 3) Vapor (a solid material condenses from a gas in which it was dissolved) For each of these we can think of everyday examples: if you have ever made hard candy, you will be familiar with the melt/solidification process, the calcium deposits on faucets and the water spots on dishes are examples of crystals derived from a solution, and frost on the window pane is a commonplace example of the vapor mechanism. In this class we will survey the most widely used gem crystallization processes, and the types of gems they produce: 240

Melt Processes: 1) Flame Fusion 2) Czochralski "Pulling" 3) "Skull" Melting Solution Processes: 1) Hydrothermal 2) Flux Vapor Process: 1) CVD Melt Processes: In each of the melt processes the powdered solid ingredients necessary to make the gem are brought to their melting point and then allowed to cool in such a way that a single large crystal or cluster of large crystals is formed. The three processes, each suitable for making different materials, differ primarily in the temperatures used, the type of container, the heat source and the nature of the surface on which crystallization occurs. 1) Flame Fusion: The process commercialized so successfully by Verneuil, is termed "flame fusion". It is simple in theory and in practice. Corundum is Al2O3, crystallized in the trigonal system. All that is necessary is to melt the raw material, aluminum oxide powder, and allow it to crystallize. If you want ruby, you just need to add a small amount of chromium oxide to the mix (Cr is the chromophore that creates red in ruby). Although the process has been scaled up for today's large factories, it is, in essence. unchanged since Verneuil's time. Synthetics produced in this manner are the least expensive, and most commonly used types. So much so, that over one billion carats per year of flame fusion synthetic corundum, synthetic star corundum, and synthetic spinel are made.

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[The Verneuil "flame fusion" process for production of synthetic gems] The powdered ingredients fall into a chamber heated to 2200 degrees Centigrade by an oxygen-hydrogen torch flame. As they fall they melt. Upon reaching a ceramic rod in the bottom, cooler, area of the chamber, they crystallize. Slowly the ceramic rod is turned and lowered creating from the melted corundum a carrot shaped crystal called a "boule". The shape of the boule is characteristic, and is not one that is found in Nature. This unnatural curved shape results in severe strain in the crystal lattice which necessitates splitting the boule in half before it can be cut. This somewhat limits the size of synthetic gemstones. It is possible (at considerable extra expense) to use a special slow cooling regimen, (similar to that used in glass blowing factories) to reduce strain, so that whole boules can be cut. The Verneuil process takes about 4 hours and results in boules, at maximum, of about 20 x 70 mm (3/4" x 2 3/4"), weighing approximately 4500 cts. Various elements can be added to create different colors (Ti and Fe for blue, for example) and rutile (titanium dioxide), can be added to create star stones. A special heating and cooling regimen is necessary for the star 242

stones in order to force the rutile to exsolve into needles, rather than remaining dissolved.

[FF synthetic ruby: split boule, faceted stone, star stone] Food for thought: Question 1: Think back to what you learned in Lesson 7 about faceting: Will a 20 mm wide split boule yield a 20 mm round brilliant? Flame fusion synthetics are among the easiest types to identify. Their most characteristic feature is curved growth rings (called curved striae) that can be seen under magnification with appropriate lighting. In addition, sometimes coloring is uneven and follows the growth, making for curved color zoning. In the single crystal gems made by Nature, there are never any curved growth features or curved color zoning, so their presence is a dead give away. The presence of bubbles is also occasionally a tell-tale sign.

[Curved striae seen in a cut synthetic ruby at 25X, under diffused lighting] Wouldn't you know it? It is sad but true that, as consumers and marketplace watchdogs become more knowledgeable and sophisticated about gems, the deceivers get trickier. This is the case with flame fusion synthetics which are being passed off as natural--> by reheating the cut gems to near their melting point the growth layers can be partially fused with the result that the appearance of the curved striae is diminished, making these pieces harder to identify. 2) Czochralski "Pulling": It was the needs of science and industry, rather than those of the jewelry trade, which prompted the development of the Czochralski "pulling" melt process. Emerging laser technology demanded 243

larger diameter, strain-free, higher clarity crystals than could be produced by the flame fusion process. Only later did the jewelry market begin to eagerly absorb some of the production. In this process, the gem source materials are melted in a metallic (usually platinum) crucible using radio frequency energy. A thin, flat, seed crystal (either natural or synthetic) is lowered to just touch the surface of the melt, then slowly rotated and withdrawn ("pulled"). The slower the rate of pulling, the larger the diameter of the resulting crystal boule. The seed gives the solidifying materials both a surface on which to crystallize, and an an atomic scale "pattern" to follow. This seed area is generally removed before the rough is sold. Although many exotic materials (like gallium arsenide) are made for exclusively for industry, YAG, corundum, Alexandrite, and cat'seye Alexandrite are the major gem materials produced by this method. Production expenses are much higher than those of the simple flame fusion process, so the products are more costly as well.

[Green YAG: a simulant for emerald and Tsavorite garnet, and a durable, brilliant material in its own right] Pulled synthetics are very difficult to identify microscopically as the crystal that forms on the seed is usually flawless, and the large diameter of the boule makes observing the curved striae difficult. On occasion, they may contain triangular or hexagonal platinum crystals eroded from the walls of the crucible, which will conclusively identify the piece as synthetic.

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[The very subtly curved striae seen on a magnified photo (25X) of the pear shaped green YAG shown above, would be easy to mis-identify as straight, the triangular platinum crystals in this magnified synthetic Alexandrite are a dead giveaway, though: Image courtesy of Martin Fuller] Food for thought: Question 2: Why should larger diameter boules make for less obviously curved striae? Question 3: If you were an honest seller of synthetic ruby jewelry why might you pick flame fusion material, and if you in the same business dishonestly, why might your choice be pulled synthetics instead? 3) "Skull" Melting: The commercial production of cubic zirconia, first accomplished by Russian scientists in the 1970s, required some ingenuity. The melting point of CZ is well over 2300 degrees C, which rules out the use of metal or ceramic crucibles. The problem was solved by using an externally cooled crucible filled with the powdered ingredients and then heating it with focused radio energy that melted only the center. The unmelted material formed its own insulation, or "skull". As the melt slowly cooled, large, usually flawless, crystals were formed. **Check the text: see page 327 in the Lyman book for a figure representing the basics of the skull melting set up. At present, CZ is the only material produced in this way, and costs are kept down by the large yields from each batch (currently the retailprice of CZ rough is about $.05 per carat). Various colors are produced, but for the great majority of CZ is sold in its colorless form as a diamond simulant. Although it is easy to identify by its optical and physical properties like density, thermal conductivity, and dispersion, microscopically, there are few signs of CZ's synthetic origin. Rarely, tell-tale bubbles can be seen. (I had to examine quite a few CZ pieces before finding this one lone bubble to photograph).

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[Colorless CZ, today's diamond simulant of choice, few inclusions or growth features, other than an occasional bubble, give clue to the synthetic origin of CZ] Solution Methods: The characteristic feature of these processes is that rather than being melted, the source materials are dissolved in a solvent (not always water), and put under high temperature and pressure. The supersaturated solution is slowly cooled, and the gem crystallizes onto a natural or synthetic crystal "seed". If the solvent is water, the process is termed "hydrothermal", if it is another substance, then the process is called "flux". Because of the high temperatures and pressures involved, strong sealed metal containers are used to hold the solutions. Some gems, like emerald and quartz, can only be made by solution methods. In other cases, such as with ruby and sapphire, solution methods are an alternative method of production. Perhaps some of you remember crystal-forming demonstrations in junior high school science class. If not, the basics of this idea can be summarized by thinking of the formation of "rock candy".

[Rock candy: Image courtesy of www.michigan.gov]

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This old fashioned treat is simply very large crystals of table sugar (sucrose) on a string. It is made by dissolving sugar in hot water until the solution is supersaturated (more sugar than will dissolve at room temperature). A wet, rough surfaced string, is rolled in dry table sugar, then hung in the solution, which cools and from which the water slowly evaporates. The dissolved sugar then crystallizes on the string. (If no string is present, the sugar will simply crystallize as a mass on the bottom and sides of the container.) **Check the web: Here is a web site with a step-by-step recipe and directions for making rock candy--> this might be a fun family project: http://www.michigan.gov/hal/0,1607,7-160-15481_19268_2077852395--,00.html Food for thought: Question 4: What is the purpose of rolling the string in the dry table sugar, wouldn't the string itself provide a surface for crystallization? 1) Hydrothermal: As the name indicates, this type of process uses water as the solvent. The vessel in which the gems form is lined with silver and referred to as a "bomb". (One can only speculate as to how it got this nickname, however, if you've ever misused a pressure cooker in your kitchen, you might have an idea!). Hydrothermal synthetics are relatively expensive, as the equipment used is pricey, and the yields are small and slow to form (weeks to months). Because this process so closely mimics what occurs naturally in the Earth's crust, the majority of inclusions in such gems are natural looking, making them hard to identify. Occasionally, cut gems will show part of the seed plate or a distinctive non-natural looking inclusion called a "nailhead spicule". The primary gems produced by this method are emeralds, corundum (especially ruby) and quartzes in a variety of colors including blue.

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[Hydrothermal synthetics: emeralds: Image courtesy of www.thaigem.com, rubies: Image courtesy of Tairus Corp. and a large chuck of colorless quartz: Image courtesy of www.faceters.com] 2) Flux: In some cases the solvent in which the gem source materials are dissolved is not water, but another material like lead fluoride or boron oxide, called a . These materials have in common that they have a lower temperature of cystallization than the gem. As the temperature in the crucible is lowered, then, the gem crystallizes first, separating out of the stillliquid flux. The process is slow and expensive. The highly corrosive nature of the fluxes means that crucibles must be made of a very resistant metal like platinum, iridium or gold, and the process can take months. Ruby, sapphire, quartz, emerald, Alexandrite, YAG and red spinel are the major gems produced in this way. Although expensive as synthetics go, the resultant gems have natural looking inclusions, the most notable of which are sometimes called "wispy veils". Consisting of crystalized flux within minute cracks in the gem, they are so like natural fingerprint inclusions in their appearance that it takes a well-trained eye to discriminate them.

S [Flux rubies, magnified "wispy veil" inclusions in a flux grown synthetic ruby Images courtesy of www.thaigem.com ] Vapor Method: The third possible way to make gems synthetically is by vapor deposition. At present only diamonds (see below) have been made this way. "Synthetic" Cabochon Gems* *(In discussing the following types of man-made materials, I will be putting the term, synthetic, in quotes. Although these gem substitutes are chemically and physically as close to the real thing as it is currently possible to make them, they still lack some of the crucial attributes of their natural counterparts. To 248

strictly observe the niceties of gemological jargon, I should call them simulants, but as they are sold and generally discussed as synthetics, I'll simply use the quotes.) Into this category go "synthetic" corals, turquoise, and opals all of which, (compared to the true synthetics above) are relatively easy to separate from natural. Under magnification each of them reveals its man-made characteristics: the coral lacks the characteristic biological ultrastructure of natural coral, the turquoise has a slightly bumpy surface, reminiscent of Cream of Wheat cereal that is most unlike that of natural stones, and the opal, shows an unnatural and distinctive "chicken-wire" hexagonal structure that gives it away.

["Synthetic" coral, "synthetic" turquoise]

["Synthetic" white opal, characteristic "chicken wire" color pattern of "synthetic" opals, 25X magnification] Diamond Synthesis The first successful synthesis of diamond was accomplished in 1955 by scientists at General Electric Corporation. These were tiny, .15 mm. crystals meant for industrial use. By 1958 the cost of synthetic diamond "bort" was competitive with natural, and today industrially produced diamond abrasives dominate the market. Besides their obvious superiority as abrasives, industrial diamonds find other applications as heat sinks and corrosion protectors. GE is still a major player, but shares the world market for industrial diamonds with Sumitomo and DeBeers Corporations. HTHP: General Electric was also the first to produce gem synthetic diamonds in 1970. These were small and quite yellow. The nitrogen in 249

atmospheric air incorporates into the diamond during the formation process, and acts as a chromophore giving the resulting crystal a yellow color. GE's method, in essence, attempts to replicate the conditions deep within the Earth's mantle where diamonds form naturally. Called HTHP (high temperature, high pressure), this, still somewhat secret process, involves a metal solvent/catalyst, 60,000 atmospheres of pressure, and temperatures of at least 1500 degrees C. The machines in which the diamonds are formed are called "presses". For the last thirty years or so, synthetic gem quality diamonds have been largely a laboratory curiosity as they cost more to produce than it would cost to obtain equivalent stones naturally. All this is about to change! Several companies are now involved in producing, or gearing up to produce, gem synthetic diamonds for the jewelry market. Gemesis and Chatham are two manufacturers of note->Gemesis is already in the retail sales mode, specializing in intense yellow colors with gems nearing 2 cts, while Chatham is poised to enter the market shortly with pinks and blues as well as yellows. To date, the high expenses and difficulties in attempting to keep the yellow color out, have given little motivation for the HTHP manufacturers to try to compete in the colorless diamond market. Fancy color diamonds are a much more profitable product. It remains to be seen if the public will be willing to pay the, still very high, prices (about 30 - 40% the price of natural fancy color stones) for synthetics.

[Gemesis created fancy color diamonds: Image courtesy of Gemesis Corporation, Chatham created fancy color diamonds: Image courtesy of Tom Chatham]

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[Diamond "Presses" engaged in producing synthetic diamond by the HTHP method: Image courtesy of Gemesis Corporation] CVD, Chemical Vapor Deposition: The third of the possible gem synthesis processes (condensation from a vapor) has been pioneered, by Apollo Corporation, for the production of diamonds. In this approach, a vacuum chamber (at .1 atm of pressure) containing a thin diamond seed crystal is filled with methane gas (CH4) at 1000 degrees C. At that temperature and pressure regime, the carbon in the gas separates from the hydrogen, and crystallizes upon the diamond seed surface. Early on, the resulting crystals, which were wafer thin, were intended for industrial applications, primarily as the future generation of heat resistant computer chips. As the methodology has improved, thicker and thicker crystal wafers have been formed. At present, Apollo gem quality diamonds of .25 ct have been cut. Compared to HTHP diamonds, they are relatively white and have high clarity. It looks as if it won't be long until gem synthetic diamonds are a profitable side-line for this company.

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[Vacuum chamber used by Apollo Corporation for CVD diamond synthesis: Image courtesy of Apollo Corporation]

[The first batch of cut "gem" synthetic diamonds produced by CVD: Image courtesy of Apollo Corporation] **Check the web: Apollo's novel approach, and good looking results have gotten several rounds of media coverage since the first gem diamonds were submitted in August, 2003 to GIA for analysis: Here's an early example from USA Today:http://www.usatoday.com/money/industries/technology/2005-10-06man-made-diamonds_x.htm What does the diamond world think of all this?? One of the hottest topics of discussion in gemological and jewelry marketing circles these days, is synthetic diamonds and their potential impact on the natural diamond market. Although some analysts have been quick to cry doomsday, and predict the fall of the natural diamond industry, the majority opinion is that created diamonds were inevitable, and having arrived, should be viewed as a positive development. Enhanced and manmade diamonds are expected to share the market with natural origin/natural color stones, as have synthetic and enhanced rubies, sapphires and emeralds with their natural counterparts. The major concerns within the industry have been those of 1) disclosure 2) identification and 3) cost.

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1) Disclosure: At present, the major companies producing gem synthetic diamonds have taken pains to identify their products as synthetic, and are selling them only through reputable and licensed jewelers. Gemesis for example, puts a laser inscription on the girdle of all its .25 ct or larger gems. (Unfortunately, it is a relatively simple matter to remove this ID after the gem leaves the store, and there is evidence that this is already happening).

2) Identification: The conclusion that the market is large enough for both synthetics and natural stones is based on the assumption that the two can be reliably discriminated. Although HTHP gems have tell-tale features that enable a well trained and well equipped gemologist or jeweler to identify them, CVD diamond recognition currently is possible only for major laboratories. The statement below was issued as part of official press release by GIA. "The major laboratories can conclusively identify gem synthetic diamonds" William Boyagian, President of GIA, 9/19/03 3) Costs: Unlike diamond simulants which can be detected with a simple, inexpensive electrical conductivity tester, synthetic diamonds, are diamonds and therefore pass all the standard physical and optical tests, as diamond. DeBeers Corporation (the company that controls the majority of worldwide diamond rough sales) has been in the forefront of synthetics detection, and offers two table model devices (costing over $20,000) that can identify HTHP stones. TheDiamondSureTM which tests for a specific 415 nm absorption line, and gives a reading of either: "natural" or "refer", and theDiamondViewTM which detects characteristic strain patterns and can conclusively identify the HTHP synthetics amongst the "referrals".

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[Licensed for sale through GIA-UK, this "DiamondView"TM instrument can be used to conclusively identify HTHP diamonds: Image courtesy of GIA-UK] CVD diamonds cannot be reliably detected even with these instruments. The average neighborhood jeweler is understandably concerned about the costs that will inevitably ensue as verification of natural origin in diamonds becomes the sole pervue of the big labs. (Testing with Raman Laser Spectroscopy and Fourier Transform Infrared Spectroscopy at the temperatures of liquid nitrogen, doesn't run cheap). To grade or not to grade, that is the question... Very heated arguments can be started among those involved in the diamond business over whether synthetic diamonds should be graded (for color and clarity) or not. GIA, AGTA and most other big gem labs have taken the position that they will identify synthetics, but will notgrade them. It is their assertion that synthetics, have no inherent value, and, as such, should not be graded. EGL (European Gem Labs) and its American subsidiary, EGLUSA are grading the synthetic stones for clarity and color. Their philosophy is that customers want their stones graded, and they are providing a desired service. Cultured Pearls: Before discussing cultured pearls, let's take a brief look at natural pearls. Natural pearls are very rare today, but they were always rare. The product of a mollusk's reaction to an irritant, such as a stray bit of shell or a parasite, they take many years to grow to useable size, and few individuals within a population of mollusks will ever make them. Beyond that, the majority of pearls in Nature are small, baroque in shape, and few are blemish free. Throughout most of history, natural pearls were the rarest and most highly valued of all gemstones.

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Here are some examples of natural pearls and how they were used. As the vast majority of pearls that were collected were tiny, those who could afford pearls, but didn't have the budget of Cleopatra or a Roman Emperor, often used seed pearls (2 mm or under). Matched strands of larger round pearls, though quite expensive, were very small by today's standards, and not perfectly uniform in either size or color.

[1870's seed pearl necklace, the tiny pearls are sown onto a mother-of-pearl backing with horsehair to make the pendant, and strands of them were twisted for the chain: this was a popular style among elite brides in Victorian England, a 16" Art Deco Era natural pearl strand, the pearls grade from 3 mm to 4.5 mm] **Check the text: The picture on page 278 of the Lyman book will give you a good idea of the color and size variability of natural pearls and the pictures on page 281 will show their typical baroque shapes. Then along came Mr. Mikimoto! At the turn of the 20th century, there were several individuals experimenting with culturing pearls, and in 1906 the first batch was grown. It remained, however; for Kokichi Mikimoto to both scale up the process to mass production, and market the products successfully to an initially skeptical world. By the end of the 1920's cultured pearls were an accepted part of the pearl marketplace, and today they are the marketplace. Except for those found in some antique and vintage jewelry items, and a few natural pearls sold to collectors, all the pearls in commerce are cultured. "Cultured" was a term that was hotly debated initially, with many feeling that the term "synthetic" should be used to clearly specify their non-natural origin, but Mr. Mikimoto won that fight. (Regardless of terminology, though, cultured pearls are not natural gems, their origin is the result of human intervention.). 255

Different Types of Pearls There are two basic types of pearls (be they cultured or natural). A pearl that forms within the body cavity of the mollusk, and has a three dimensional shape, sometimes round, is a "cyst" pearl. One that forms attached to the shell of the animal, and therefore has a flat back surface is known as a "blister" pearl. Possible colors of pearls vary with the species of mollusk, but usually are some shade of the color of the shell lining of the animal. An assembled, cultured, blister pearl product is known as a "Mabe" pearl. They are grown by gluing a plastic or shell half dome or other shape (nucleus) onto the inside surface of a mollusk's shell. Once the nucleus is coated with nacre, the blister pearl is cut away from the surrounding shell. The nucleus is removed and the cavity is filled with an epoxy resin, and backed by mother-of-pearl. Mabe pearls are quite attractive, less expensive alternatives to cultured pearls of the same diameter.

[Cultured pearls: cyst pearl, blister pearl, Mabe "pearl" pendant] Natural pearls come from mollusks native to both saltwater (oysters) and freshwater (mussels), and cultured pearls can be produced from both types of mollusks. Two different strategies are used in culturing: bead and tissue nucleation. Saltwater: Saltwater cultured pearls are "bead nucleated", meaning that a round bead of shell is used as the "irritant" around which the oyster secretes the nacre. The company that Mikimoto founded is still going strong, and specializes in the highest quality saltwater cultured pearls from the Akoya oyster. Such pearls are white to silver or cream, often with pink overtones. They tend to top out at about 8 mm in size, and those pieces with relatively thick nacre layers due to long cultivation periods, have a fine luster. 256

Larger pearls, such as Tahitian blacks and Indonesian golds, are cultured in oyster species from the tropics, and can attain sizes of 20 mm or greater. Saltwater cultured pearls can be rather expensive depending on size and quality.

[Mikimoto Akoya saltwater cultured pearls: this 18" strand of 8 mm round pearls retails for about $3000]

[10 mm cultured Tahitian black pearl ring, 10mm is considered small for a Tahitian and this piece can be had for under $200] In the picture below an oyster is being nucleated with a shell bead. You can see the animal in the holder, and the dish of beads. Expert nucleators command respect within the industry as skilled professionals, and are very highly paid.

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[Pearl nucleation: Image courtesy of Dr. Jill Banfield] Freshwater: Freshwater cultured pearls are almost always "tissue nucleated" which means that only a slice of mantle tissue from a donor mussel is used to start the culturing process, there is no shell bead. As is the case with natural pearls, a tissue nucleated freshwater pearl is virtually all nacre. Historically, freshwater pearls were first produced from Lake Biwa in Japan, but today most come from China. The original "Biwa" pearls, introduced in the 1970's were small with flat, baroque shapes--> they were sometimes referred to, dismissively, as "rice crispies". You can see in the second photo below that things have changed, and today's freshwater cultured pearls are large and approach a perfectly round shape. Freshwater pearls remain inexpensive: the strand at the left retailed when new (1980's) for about $30 and the 18", 7.5 mm strand to the right currently retails for under $200.

[Freshwater cultured pearls: Original-type Biwa pearl strand, contemporary near round 7.5 mm strand] 258

Identification: Many saltwater cultured pearls can be identified by microscopically viewing the drill hole and observing the demarcation between the shell nucleus, and the nacre layer on top of it. In difficult cases, and with freshwater cultured pearls, Xrays will do the job. The bead nucleus shows up clearly in the radiographs, as does the smaller area where the mantle tissue was placed in a freshwater cultured pearl. There is actually little chance, though, that today's fresh or saltwater cultured pearls would be mistaken for natural pearls. To anyone who has studied natural pearls, today's creations are so large, so round, and so well-matched in color, that the difference is obvious. Making the call between enhanced and unenhanced is another matter though. As you recall from Lesson 8, most cultured pearls are enhanced in one way or another.

Simulants Also known as imitation or faux gems, simulants look like what they imitate, but they don't have the chemical, physical and optical properties of the gem they mimic. (**Just a reminder from Lesson 1, simulants are only fakes if they are not properly disclosed.) Some are man-made, and some are natural gems in their own right. Early Simulants The history of gem simulation goes back every bit as far as that of gem enhancement. Since before 3000 years ago Egyptians have been making faience, a beautiful blue to green non-clay ceramic material. The colors are derived from copper or other metals and, although used and admired for its own sake, it has also commonly been used to imitate turquoise and lapis lazuli.

[Faience "mummy" beads, circa 300 BCE (newly re-strung to wear), 1880's Victorian "Egyptian Revival" brooch featuring "plique a jour" enamel and an ancient faience scarab]

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The technology required to make faience is similar to that necessary to make glass, which the Egyptians also mastered. Glass making skills are believed to have traveled to the Greco-Roman world from Egypt, and by 1000 BCE, the Romans began casting glass. (Glass blowing came along much later).

[A fragment of circa 500 CE Roman glass made by blowing molten glass into a mold (the iridescent surface patina was not a glaze or paint put on by the Romans, but has been slowly created by chemical reactions, between the glass and soil, occuring over centuries of burial, these reactions creates a thin layer of metal oxides)] Simple glass beads and cabochons were in used in jewelry--> in fact they were enjoyed only by the wealthy, as these technological marvels of the day were more valuable than most natural gems!

[Circa 1000 CE Chinese glass bead (on modern chain), Roman bronze and glass cabochon ring circa 100 CE] Natural Gems as Simulants: It is very common for one natural gem to be used to imitate another of similar appearance. For example serpentine, aventurine quartz and hydrogrossular garnet, all have long histories as jade simulants. Likewise, bone is a common substitute for ivory, and white zircon has long been enjoyed as a natural diamond simulant. Red spinel commonly is substituted for ruby, sodalite for lapis lazuli, and copal for amber.

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[Natural Simulants: bone carving (ivory), red spinel (ruby), sodalite (lapis lazuli), copal, a natural, geologically younger, partially fossilized tree resin (amber)] Man-made Simulants: Glass and Plastic Glass: Although its historical roots go way back, glass is still one of the most popular gem simulants today. Glass, itself, is an amorphous material, but its main raw material, silica sand (quartz), is crystalline. In glass-making sand is mixed with certain other materials and melted; then it is cooled so quickly that crystallization doesn't occur. Some scientists describe glass as a liquid that is so stiff that it behaves, superficially, like a solid. This assertion is supported by the observation that very old glass windowpanes are thicker at the bottom than at the top, and the older they are, the more this effect is seen. Two quite different forms of glass are used to simulate gems: crown glass and flint glass. Crown Glass: is used for ordinary windows and bottles, and is also known as common, or silica glass. When gems are made from it, it is often called "paste". This sort of glass is relatively soft, has a low refractive index, a low specific gravity, and virtually no dispersion. Due to its lack of brilliance (a consequence of the low refractive index), a metallic foil or paint was often applied to the back facets of such gems (called "foilbacks") to increase reflectivity. Flint Glass: is also known as "crystal", "strass" (named after the 18th century inventor), or "leaded glass". This very soft, easily scratched glass has a high refractive index, high specific gravity, and high dispersion. ** Check the web: Just about the most famous producer of gem "crystal" (highly dispersive leaded glass) is the Swarovski company, visit their site at: http://www.swarovski.com/ The natural color of glass is a light green (perhaps you have seen or remember the color of the original "Coke" bottles), but it can be de261

colorized or colorized chemically. By adding different colorants (chromophores), spectacular hues can be achieved, like purple (manganese), dark blue (cobalt), and red (gold). Identifying glass: Many paste gems are molded rather than faceted, and as such, have notable surface characteristics, such as sunken facets, an orange peel surface, or mold lines. Even if glass is faceted, its softness often results in facet edges that are slightly, to noticeably, rounded compared to the knifeedge facets of harder gems. Physical and optical characteristics are also useful in identifying glass. The typical bubbles and swirls, seen under magnification, have already been mentioned in Lesson 5. Added to this are the low hardness (4-6, depending on the type of glass), the characteristic brittleness, and the conchoidal fracture with its vitreous luster. Furthermore, the relatively low thermal conductivity of glass makes it feel somewhat warmer in the hand than crystalline materials. As an amorphous substance, glass will give a polariscope reaction of SR, and in terms of density the specific gravity of crown glass is less than most common gems, while the specific gravity of flint glass is higher. Historically, glass has been used to imitate just about every kind of gem. Today, however, glass is most commonly used to simulate translucent gems such as opal and chalcedony, and opaque gems like jet, lapis and coral. (Over the last 100 years or so, the availability of synthetic gems has dramatically decreased the popularity of glass "rubies" and other faux transparent gems). Even phenomenal gems such as moonstone, sunstone and pearls have glass simulants. Faux pearls had their heyday of popularity before the advent of pearl culturing, but many types are still made today. Commonly they are made of translucent glass beads that get a many-layered coating of lacquer containing pearly looking "essence d' orient" (made from ground fish scales!). The moral of the story for the gemologist is: "Always suspect that the "gem" you are looking at is glass--> and test for this possibility."

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[Foil-backed glass "Rhinestones" circa 1950, a glass jade simulant showing typical bubbles under magnification: Image courtesy of Martin Fuller]

[Man-made aventurine glass, "goldstone", obsolete glass opal simulant, "Slocum Stone": Image courtesy of Dr. Jill Banfield, carvings made of a modern glass opal simulant, "Opalite": Image courtesy of Las Vegas Jewelry and Mineral, a glass faux pearl showing scratches in the painted-on surface coating] Plastic: Most people would be surprised to learn how far back the manufacture of plastics goes. By the late 1800's the "plastic age" was well into its beginnings. The earliest plastics, like vulcanite, Bakelite, celluloid and lucite were used for a wide variety of purposes, including among them gem simulation. Some of these early materials found use as imitations of jet, ivory and tortoise shell, making copies of these luxury organic gems available to a large audience. Plastic jewelry peaked in popularity in the 1950's, but still finds use today, mainly in the cheapest of simulants (the sort you might get from a gumball machine, or as a prize at a carnival). Visually, plastics can be recognized by the greasy to sub-vitreous luster, rounded facet edges, surface craters or pits, and the presence of mold marks. The surface of its fracture has a dull luster. Microscopically, plastics have swirls and bubbles similar to those seen in glass. They give an SR reaction to a polariscope test. 263

Plastics are quite soft, with hardnesses ranging from 1.5 to 3, and both the refractive index and specific gravity are low. Even more so than with glass, the low thermal conductivity of plastics makes them warm to the touch. When touched to the surface of plastic, a "hot point" tester will release an acrid chemical smell that is quite distinctive. (Here's a method of identification that I wouldn't recommend with a prize antique: drop the piece from about 5 inches onto a hard surface like a desk top. Plastic makes a hollow sound compared to the higher pitched, sharper sound made by either glass or crystalline gems.) Glass is a more convincing simulant of transparent gems, but plastic does a good job imitating translucent and opaque stones like amber, turquoise and coral. (A sizable percentage of the least expensive Southwestern sytle "turquoise" jewelry is actually plastic.) Certain optical properties of some types of plastic can be utilized do a good job of simulating phenomenal gems like opal and moonstone.

[Contemporary plastic gem simulants: imitation opal, faux pearl (note mold mark), molded plastic "cameo", simulated plastic moonstone drops on a glass"crystal" bead bracelet]

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[Antique and vintage plastic simulants: circa 1870's vulcanite brooch (jet), 1890's celluloid brooch (ivory), 1940's plastic "moonstone" dress clip] Diamond Simulants The bad news in regards to diamond simulants is that there are a multitude of them, no other gem has been so often imitated. The good news is that allof these mimics can be discriminated by either simple observation, or by basic gemological testing-->no big labs needed! The oldest diamond simulants were glass, and colorless natural gems. With glass, first came the older crown type (usually with a foiled back to increase reflectivity), and later the more brilliant and dispersive flint glass. The natural gems white topaz, sapphire, zircon and quartz were also used, but at a higher cost than glass. (If you are skeptical that glass or quartz could make a reasonable approximation of a diamond, consider that with the simple early diamond cutting styles, and the polishing technologies available prior to the 20th century, diamonds were not the blindingly brilliant gems of today.) Synthetic diamond simulants enter the picture around 1910 when colorless sapphire was first produced by the flame fusion process. This was followed by the introduction of colorless synthetic spinel (1920), synthetic rutile (1948), strontium titanate (1955), YAG (1960), CZ (1976), and Moissanite (1996).

[Diamond simulants natural and synthetic: white zircon, synthetic rutile, strontium titanate, YAG, CZ, Moissanite] Identifying Diamond Simulants

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Glass: Crown glass is notably softer, less dense, less brilliant, and less dispersive than diamond. Flint glass though dispersive, is more dense, and much softer. Both types have a vitreous luster, as opposed to the adamantine luster of diamond. Natural Gems: Depending on the species, the RI, the density, or the dispersion would be the give away, and all the commonly used colorless natural gems are DR, so a polariscope test would easily separate them from the SR diamond. Zircon, the closest to diamond in appearance is not only DR, but so strongly birefringent that it shows doubled rear facet images when viewed with a loupe. Synthetic Sapphire/Synthetic Spinel: Although hard, corundum is a DR gem and its RI of 1.76 (diamond's is OTL), and lack of dispersion is telling. As spinel is an SR gem a polariscope test wouldn't help, but its RI of 1.72, hardness (8), and low dispersion would be the best indicators. Synthetic Rutile/Strontium Titanate: These gems enjoyed a period of brief popularity after their introductions, and are sometimes seen in vintage pieces. Indentification is a simple matter though, as their extremely high dispersion makes them very easy to spot, and their softness makes them noticeably fragile compared to diamond. YAG: Although hard (8.5) and SR, YAG is so lacking in dispersion that it, too, can be easily separated from diamond. CZ: The remarkable popularity of CZ is, in my opinion, well deserved: hard (9), SR, and not too noticeably more dispersive than diamond, it passes most visual tests well, but testing for density will reveal it every time, as it is much heavier than diamond. (In addition, all of the simulants above will "fail" a thermal conductivity test.) Moissanite: This is the latest contender, and like CZ, it is hard (9.5), and not so overly dispersive as to be obvious. It will pass a thermal conductivity test as diamond, but its electrical conductivity will invariably identify it. In light of this, a new generation of "diamond testers" is being highly promoted as indispensable to those concerned with guarding against bogus "diamonds". Such equipment not really necessary though, as Moissanite is DR, and will flash "on and off" with the polariscope test described in Lesson 4. Even without fancy gemological equipment, all that is needed is a loupe, and a 266

little knowledge. Moissanite gems are deliberately cut on an optic axis so that when you look down through the table you see sharp facet reflections (no doubling) as if the stone were SR. By tilting the gem on its side, and viewing the back facets with a loupe, the strong birefringence of this DR gem will reveal itself by the presence of doubled facet images, something you'd never see in a diamond-->no matter which direction you turned it.

[Magnified view of doubled facet reflections in Moissanite]

Assembled Gems Also known as composite gems, assembled gems are made of two or more pieces of gem material joined together. They can be used as to simulate (or fake) another gem, or just for their own sake, for example to make an artistic gem creation, or to make a particular gem material more durable or useable. Assembled Gem Art Intarsias, insets, inlays, pietra dura and micro-mosaics fall into the category of making something beautiful out of what would otherwise have been waste products. These lovely works of gem art are often made of the small bits and pieces left over from, or too small for, other lapidary activities.

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[Contemporary pieces: black onyx/precious opal intarsia, black onyx/rock crystal assembled carving, faceted citrines with garnet insets, multigem intarsia]

[Antique pieces: 18th century "pietra dura" (hard stone) style intarsia locket: Image courtesy of www.fraleigh.com, and micro-mosiac (glass) brooch, 10X close up of micro-mosaic: Images courtesy of Acanthus Antiques] Increasing Durability Doublets and triplets are generally made either to increase the durability of a fragile gem or to support and protect a thin slice of gem material. Usually a doublet consists of a thin layer of some valuable, fragile, or rare gem material backed with a thicker layer of something sturdy, and less expensive. If the piece is unmounted, or set in prongs, it is usually very easy to see the demarcation line between the top and the bottom. Sometimes the backing is simply used to provide contrast or create an artistic effect. A triplet is a doublet with a third, top, layer made of a tough transparent material like colorless quartz.

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[Black opal doublet, the same piece viewed from the side at 10X, opal triplets (note black bottom layer and colorless top layer): Image courtesy of Gary Lowe, rutilated quartz doublet with a green Gaspeite bottom layer] Assembled Gems as Simulants and Fakes Historically, assembled gems were more important as gem simulants and fakes in the days before synthetics became widely and inexpensively available. You are more likely to see them in vintage and antique jewelry pieces., but there are still a few cases, where assembled stones are used as gem stand-ins, and some unscrupulous folks are still trying to pass some types off as something they aren't. Not for Deception Mabe pearls, as described in the cultured pearl section above, are examples of assembled gems which are produced with no intent to deceive. They always have flat backs and mother of pearl bases which easily distinguish them from regular cultured pearls.

[Black Tahitian Mabe pearl earrings] The green stone below is a simulated "Soude" emerald such as is regularly used in the marketplace today. Usually, at least at the retail level, there is no intent to deceive, and these are sold widely and openly as an imitation May birthstone (emerald). A Soude is actually a three piece assembled gem--> a triplet. The top and bottom layers are made of colorless synthetic spinel created by the 269

inexpensive flame fusion process. The middle layer, depending on the manufacturer is either green glass or, as in the stone below, green glue. Because the stone is faceted, when viewed from the top with light reflecting throughout its interior, selective absorption from the green layer makes the stone look uniformly green. It is not uniformly green, though, as you can see in the second photo, where the stone has been immersed in liquid and is viewed from the side. The colorless top and bottom are clearly visible. Once the stone is set however, such a test is difficult to do. Another "tell" for an unmounted or prong mounted piece of this type, is the magnified view of the girdle area. As the third photo below shows, the "join" or seam between the crown and pavilion, is visible. In a single-piece gem, no such line would be there, the girdle area would be unbroken.

[Not for deception: imitation "Soude" emerald (a synthetic spinel triplet), immersed side view, magnified girdle view] Deception Intended The classic case of deception with an assembled stone is the "garnet and glass doublet" which was used throughout the 19th and early 20th centuries to mimic various colored transparent gems. In these clever concoctions, the bottom and most of the top of a piece of "rough" is constructed from colored glass to which a thin slice of natural (red) garnet has been fused or glued. The rough is then faceted so that the thin sliver of garnet forms some of all of the crown area of the gem. The color of the glass pavilion is all that shows face up, especially when the doublet is mounted. The garnet top provides high luster and good durability that the glass bottom lacks. By microscopic examination, or immersion and viewing from the side, the deception can be seen, but once mounted, these frauds almost always escape detection.

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** Check the text: The Hall book has pictures and information on classic G&G doublets on both page 37 and page 61. (She calls them "garnet-topped doublets") In today's marketplace there are still a few doublets and triplets being manufactured to fool the unwary, but due to the low cost and easy availability of synthetics, they are not as common as they once were. Some examples that jewelers and auction houses occasionally still see are YAG/strontium titanate doublets (as diamonds), synthetic ruby/ruby doublets (as ruby), and beryl triplets (as emerald). Food for Thought: Question 5: Why would a YAG and strontium titanate doublet be a better diamond simulant than either material by itself?

[Contemporary synthetic ruby/ruby doublet showing "join" at the girdle: Image courtesy of www.thaigem.com, vintage garnet and glass "sapphire" shown under immersion and as a microscopic view of the crown area: Image courtesy of the Canadian Gemology Association, circa 1910 garnet and glass "emerald" ring: Image courtesy of Sunday and Sunday Antiques] Detecting Assembled Stones Detecting assembled stones can be as easy as simply looking at them, as in the case of intarsias or inlays, but in other cases careful testing is necessary. The best bet for a gemologist, jeweler or collector is to always check the RI of both the crown and pavilion of the stone, and observe both the crown and girdle area under magnification and under immersion if possible. Prong mounted gems can usually be examined adequately as is, but bezel set stones (especially those with completely closed backs) often must be dismounted if their identity is to be conclusively verified. Answers to the thought exercises for this lesson. (If you don't understand something in these answers it's time to email me and ask!)

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1): A cylindrical boule that is split down the center will have a depth of 10 mm, so theoretically the maximize sized round stone you could get would be 10 mm. In practice it would have to be even less than that in order to insure there was no window. 2): Think of cutting a cherry in half and compare the rate of curvature of the outer edge with an orange cut in half. The larger the circumference the more gradual is the curve. When you are looking at a faceted gem you are looking at a tiny little sector of a boule--> the larger the boule it was cut from, the less curvature you will see. 3): An honest synthetic ruby seller will go for the lower priced flame fusion material whereas the dishonest one might opt for the more expensive, but harder to identify, pulled material. 4): The tiny sugar crystals not only provide a surface, they also provide a pattern to follow so that as the sugar in solution crystallizes, the ones that are already present get larger. Without this pattern to follow the sugar crystallizes in a more disorganized manner that is not so attractive. 5): A doublet made with YAG on top and strontium titanate on the bottom would be relatively hard (YAG is 8.5) and have less dispersion than strontium titanate alone (which has too much) and more dispersion than YAG (which has too little). You have now completed the web lecture for the ninth lesson! Go back the the course web site to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. When you're ready, proceed on to Lesson Ten: Gem Formation

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LESSON 10: GEM FORMATION Before venturing into a summary of the ways in which gems are formed, it would be good background to review where those processes are occurring. A crude geological model of our Earth can be made by using an apple. The Earth's crust or top layer (ranging from 3 - 25 miles deep, only 1% of the Earth's volume) is represented by the thin skin, its mantle accounting for over 80% of the volume is represented by the flesh (over 1800 miles thick), and the core is represented by, what else?, the core.

[Approximate size relationship of Earth's three layers: crust (peel), mantle (flesh), core (seeds and surrounding core)] The core has a solid inner, and liquid outer, portion, and is the least known and studied part of the Earth. Most of the mantle consists of melted rock (magma) and giant segments of the Earth's crust along with the solid upper mantle, called "tectonic plates", float on this fluid rock and move slowly over it. The movement normally occurs at about the same rate your fingernails grow, but can be substantially faster when one plate suddenly slips in relation to another. The various ways in which these plates encounter each other, are responsible for many of the momentous events that shape our Earth, such as volcanism, earthquakes, and periods of mountain building.

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[Crustal Plates: Image courtesy of www.usgs.gov] Almost all gems of mineral origin form in the Earth's crust, with the notable exceptions of peridot and diamond, which form in the mantle, and all of them aremined in or on the Earth's crust. This gemiferous crust is made up of three types of rocks: igneous, sedimentary and metamorphic, which differ in their origin and characteristics. Igneous rocks are those which solidify from a molten state, sedimentary rocks form due to consolidation of layered sediments , evaporates, or precipitates, and metamorphic rocks result when great temperature and pressure change the crystal structure of either igneous, sedimentary, or other metamorphic rocks. (Recall from Lesson One, that minerals are composed of a single substance, like quartz, and rocks are made of more than one mineral, like granite, for example, which consists of quartz, mica and feldspar.)

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[Three types of rocks: Igneous: basalt from lava flow, Hawaii, Sedimentary: sandstone hills, Utah, Metamorphic: rocks in Switzerland: Image courtesy of Dr. Barb Dutrow] **Check the web: This site, although meant for kids, is well done and worth seeing. It has animations of the conditions under which the three types of rocks form: http://www.fi.edu/fellows/fellow1/oct98/create/index.html The Rock Cycle The rocks that we find on, and under, the Earth's surface are involved in an age-old, and continuing, recycling program of Nature called the "Rock Cycle".

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[The Rock Cycle: Image courtesy of www.usgs.gov] Let's start with the red area at the bottom of the diagram: magma, molten rock. When magma rises through cracks and cools slowly underground, it forms igneous rocks composed of minerals with fairly large crystal sizes, these are known as intrusive igneous rocks. When the magma erupts onto the surface, as through a volcano, it is termed lava, and depending on the rate of cooling, the extrusive igneous rocks which form have medium to very small mineral crystals. (Review the concept of temperature and crystal size from Lesson Three, if necessary). Some lava cools so rapidly that it forms an amorphous material without a crystalline structure. Granite and basalt are examples of larger and smaller grained igneous rocks, respectively, and obsidian (volcanic glass) is amorphous.

[Granite: note coarse texture: Image courtesy of Dr. Barb Dutrow] Once the igneous rock is on the surface, the forces of erosion and weathering produce smaller particles which accumulate on the surface, and/or are 276

moved by wind and water. As time proceeds, layers of these sediments build up (on land or under water). The pressure from upper layers causes compaction in the lower layers along with various chemical and physical changes (lithification), which lead to the creation of sedimentary rock. Evaporation is an alternate factor which also produces sedimentary rocks, as when dripping mineral-laden waters leave behind stalactites or stalagmites. Likewise, surface or subterranean waters carrying dissolved minerals may evaporate or precipitate those minerals within the cracks in other rocks, or between rock layers. Sandstone and limestone are familiar sedimentary rocks formed by lithification. Opal and turquoise illustrate the evaporative mode of formation. The presence of intrusive magma in a local region (contact metamorphism), or of tectonic plate interactions on a larger scale (regional metamorphism) puts the igneous and sedimentary rocks and minerals under heat and/or pressure which may cause changes in their chemistry and crystal structure. The result is the creation of metamorphic rocks. Thus is limestone turned into marble, sandstone into quartzite, and serpentine into nephrite jade. As with most cycles in Nature there are sub-cycles and cross interactions. So, for example, sedimentary rocks which are subducted through tectonic action may melt and form magma which produces igneous rocks. Or metamorphic rocks, which have been uplifted and exposed at the surface, will erode to form sedimentary deposits. How and Where Gems Form A specific, and unlikely, combination of five factors: temperature, pressure, space, chemical elements, and time, are required for the formation of each kind of gem. This is why gems are, in general, rare-->but some are rarer than others. Silicon and oxygen are the two most abundant elements of the Earth's crust, and the conditions for the formation of quartz (SiO2) are relatively common, so it is understandable that quartz is found widely. Axinite on the other hand, which is also a silicate gem, requires (in addition to silicon and oxygen) calcium, iron, magnesium, boron and aluminum for its formation, and is much rarer. Percentage of Earth's Crust Composed of Various Elements: Oxygen: 46.60%

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Silicon: 27.72% Aluminum: 8.13% Iron: 5.00% Calcium: 3.63% Magnesium: 2.09% Boron: 0.0010% Beryllium: 0.00026% Gems, in Nature form: 1) from solutions by precipitation, 2) from melts by crystallization, or 3) from vapors by condensation. (You may recall from Lesson Eight that when Man synthesizes gems, these are also the three possible modes of production.) Solution/Precipitation Gem Formation Both near-surface, cooler waters, and warmer waters from lower depths in the Earth, can dissolve certain minerals from rocks or sediments, and carry, mix, and concentrate them until conditions change, ultimately precipitating them as solids (crystals or amorphous materials). Near surface environments: Near surface waters, like rainwater, move down or up, through soil or rock, as the local cycles of precipitation and evaporation dictate. Such water has carbon dioxide from the air dissolved in it, which creates a weak acid solution (carbonic acid) in which many minerals are soluble. If the environment contains sandy soils or sandstone rock, then silica will be dissolved, and certain silicate gems such as aggregate quartzes, like agates, or amorphous opals may form as the water evaporates. Commonly, layered or banded patterns are seen in the agates indicating cycles of formation from waters of slightly different chemistries. The botryoidal habit is also frequently seen in gems formed under near surface conditions. Likewise ocean water or other brines can evaporate as climate changes leaving behind dissolved minerals, like halite (the mineral name for sodium chloride, table salt). Other waters containing sulfur may evaporate, and leave behind sulfate minerals like gypsum.

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If the rocks or soils contain aluminum and copper in addition to silica, then copper containing minerals like azurite, malachite and turquoise may form.

[Near surface silicate gems: agate cabochon showing layered structure, botryoidal carnelian, precious opal in rock seam, common opal nodule]

[Amethyst stalactite: note layered structure of both aggregate and single crystals]

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[Minerals from briny evaporates: "cranberry halite" from Nevada, green halite from Australia (color is due to pigments from crustaceans and microorganisms that lived in the salty water), gypsum "roses": Images courtesy of Las Vegas Jewelry and Mineral]

[Turquoise bearing rock, from Nevada: Image courtesy of Las Vegas Jewelry and Mineral, rare occurence of single turquoise crystals from Virginia 50x, malachite, turquoise and chrysocolla veins in an Arizona rock: Image courtesy of Dr. Barb Dutrow, slice of a malachite and chrysocolla stalactite: Image courtesy of www.barlowsrocks.com, azurite crystals from Utah] Think about where you imagine miners finding agates, opals, and copper minerals--> you probably already know that the best deposits occur in rocky, sandy areas with an arid or semiarid climate. (Most of the world's precious opal, for example, comes from the Australian desert, and the Western USA and Mexico, are well known sites of turquoise and agate deposits).

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[Map of some of the major turquoise mines in the Southwest (photo taken at the Las Vegas Natural History Museum)] Petrifaction: Sometimes the hard, organic remains of plants such as wood or cones, or the bones or shells of animals are buried in lava or sediments before they can decay. Such burial restricts oxygen supply, and decomposition processes slow to a snail's pace. Silica laden waters can, ever so slowly, fill and replace any cavities or structures that are present with agate or opal, preserving a replica of the original form in solid rock. Many fossils are the result of this process, known as petrifaction.

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[Examples of petrifaction: slice of fossil palmwood: Image courtesy of www.barlowsrocks.com, cabochon of fossil palmwood from Texas, fragments of fossilized dinosaur eggshell, pendant with red spinel, fire agate and fossilized dinosaur eggshell, fossil wood slices from Oregon: Image courtesy of Las Vegas Jewelry and Mineral, opalized clam fossil (opal solution filled the cavity of the clam shell and solidified before the shell decayed. Remnants of the fossil shell were then cut and polished away, revealing a perfect "cast" of the original shape] Deeper Environments: Waters from deeper in the Earth are often heated from contact with hot rock, and are sometimes highly acidic or alkaline, making an even better solvent for more types of minerals. Environments where water of this type is found are termed "hydrothermal". Usually, rates of cooling and/or evaporation are slower than in near surface environments giving time for single, larger crystals to form. Many of the world's highest quality mineral specimens and metal ores have come from such hydrothermal sources. Emeralds, rock crystal quartz, amethyst, and fluorite are gems commonly formed when hydrothermal fluids solidify (as veins or crystals) in the cracks or pockets within rocks, or between rock layers.

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[Hydrothermal amethyst crystals from Mexico: Image courtesy of www.irocks.com, gold veins in quartz: Image courtesy of California Geological Survey, native copper veins in Arizona rock: Image courtesy of Dr. Barb Dutrow, hydrothermal fluorite crystals, dendritic silver in quartz: Image courtesy of www.irocks.com, Natural hydrothermal emerald crystals in matrix: Image courtesy of www.yourgemologist.com] Geodes: Cavities dissolved into sedimentary rock, or gas pocket cavities in igneous rock, are prime sites where crystallization from hydrothermal solutions occur. The results, known as geodes, usually contain agate or quartz, and are one of the favorite finds of rock hounds.

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[Small quartz geodes, huge amethyst "cathedrals": Images courtesy of Las Vegas Jewelry and Mineral, the outside and inside of a rare azurite geode from Arizona]] Melt/Crystallization Formation As magma cools, various minerals form, depending on the temperature and pressure at a particular location and time. As each type of mineral forms it reduces concentration of, or removes, some of the elements required for its formation. Thus as the mix of elements present, and the physical conditions change, so do the minerals which form. Intrusive: Gems usually form in intrusive igneous rocks where the slow rate of cooling favors larger crystals. Generally, though, we do not mine the original formation sites of these gem-containing rocks, but instead gather the weathered-out gems which have been released when these intrusive rock bodies are uplifted to the surface, or erosional processes reveal them. Corundum and topaz are examples of gems which form in intrusive rocks. Extrusive: Extrusive igneous rocks would generally not be expected to hold large crystals. Occasionally, though, some large crystals will form deep underground, but before crystallization of other minerals is complete and a typically large grained intrusive rock is produced, the magma suddenly finds its way to the surface. Under these new conditions, the rest of the magma (carrying the large crystals from below) quickly solidifies to becomes fine grained rock. In such extrusive igneous rocks we find larger gem 284

crystals in a matrix of finer grained rock. (See mantle gems, below). Corundum, moonstone, garnet and zircon are examples of gems that can be formed and brought to, or near, the surface in this way.

[Topaz crystal from China, Spessartite garnet crystals in microcline matrix from China: Images courtesy of Treasure Mounting Mining, a huge, non-gem quality garnet crystal in host rock: Image courtesy of Las Vegas Jewelry and Mineral] Gems formed in the mantle: Peridot crystals form in magma from the upper mantle (20 to 55 miles deep), and are brought to the surface by tectonic or volcanic activity where we find them in extrusive igneous rocks. Diamonds were formed many millions of years ago, deeper in the mantle (around 100 - 150 miles below the surface), at extreme temperatures and pressures. These diamond forming magmas would later erupt (still holding the diamonds) to form rocks called kimberlites and lamproites.

[Diagram courtesy of The International Gem Society and Don Clark, www.gemsociety.org] The scenario goes something like this: 1) magma, containing diamond crystals, suddenly and explosively finds a path to the surface. 2) As the lava 285

(orange) rises, some of it cools and solidifies underground forming a carrot shaped formation of kimberlite rock, in which the diamond crystals are "frozen". 3) & 4) The volcanic cone has eroded away leaving diamonds at the surface, and underground in the kimberlite (or lamproite) "pipe" (gray).

[Diamond crystal in kimberlite rock from Russia: Image courtesy of www.irocks.com, peridot crystals in basalt from Arizona: Image courtesy of www.mtlilygems.com] Pegmatites: As magma, which contains dissolved minerals in water under pressure, begins to rise through cracks and cool down, crystallization begins. The magmatic water, along with the dissolved minerals which require lower temperatures for their crystallization, becomes more and more concentrated. In the end phases of crystallization of the magma, the water is expelled as vapor, and the highly concentrated magma remnants crystallize near the surface in a distinctive geologic formation known as a pegmatite. The magmas from which pegmatites form often contain high concentrations of rarer elements like beryllium and boron. Gems commonly found in pegmatites are emerald, topaz, tourmaline, rose quartz, chrysoberyl and spodumene, and they can be very large. ** Check the text: look up the chemical formulas of tourmaline and emerald and see which of them requires beryllium, and which boron. Check page 83 in Hall to see what rare element is responsible for the pink color in rose quartz.

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[World class aquamarine crystals from N. Pakistan pegmatite: Image courtesy of www.irocks.com, pink tourmaline rough from a pegmatite formation in the Stewart Mine in California, emerald crystals: Image courtesy of Las Vegas Jewelry and Mineral, rose quartz from a Brazilian pegmatite mine: Image courtesy of www.irocks.com ] **Check the Web: One of the most famous pegmatite mines in the US is the Stewart Tourmaline Mine in Pala, California. This famous deposit, most noted for its bubble gum pink tourmaline, consists primarily of pegmatite formations of a type called dikes. Visit this link to take a virtual tour of the mine: http://www.mmmgems.com/stewart/minetr2.htm Vapor/Condensation Formation It might be a little difficult to imagine vapors condensing to form crystals, as it seems somewhat foreign to every day experience. And it's true that at normal atmospheric pressures, and common ambient temperatures, this doesn't happen very often. But there's one good example that we can all look to: frost which forms on our windowpanes or car windshields, is, in fact, precisely a situation of a vapor (water vapor) condensing to a solid crystal (ice). The next time you get a chance--> use your loupe to example that frost: beautiful! Given the extreme environments created by some geological events, such as an eruption of magma, conditions can be ideal for such condensation processes, and they are relatively common events.

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Vugs: When magma (a fluid with dissolved liquids and gases) is suddenly released from the pressures containing it (as when it erupts or spreads into surface fissures), gases are freed and liquids quickly vaporize to gas, which creates gas-filled bubbles and pockets in the lava called "vugs". (We experience a similar phenomenon every time we open a carbonated beveridge). Gems cans crystallize from these vapors which are trapped and concentrated inside the openings. Often they form singly, without attachment to the surrounding surface. When we see a doubly terminated crystal, or one that is perfectly formed with no attachment point (called a "floater"), often it has formed in just a such a gas pocket. One of the most famous deposits of these doubly terminated crystals is the rock crystal quartzes formed in Herkimer, NY, and known as "Herkimer Diamonds". Other pockets which do not produce crystals from gases, may later be invaded by surface water, or hydrothermal fluids, and become filled or lined with small or large crystals forming geodes or other similar formations.

[Spessartite garnet "floater" crystal from Namibia, doubly terminated rock crystal quartz ("Herkimer Diamond") from New York, igneous vug lined with hydrothermally derived quartz crystals, vug from Germany, containing stalagtites covered with tiny quartz crystals: Image courtesy of www.irocks.com] Crystal growth from solutions or vapors can also exploit fortuitous openings as seen below. This ancient clam's death, and subsequent fossilization,

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created a space in the surrounding rock which later became home to the beautifully formed calcite crystals in this prize specimen.

[Fossil clam shell with calcite crystals, from Okeechobee County, Florida] Changes after Formation (Metamorphosis) As mentioned previously, heat and pressure from contact or regional sources can cause one mineral to metamorphose into another. This frequently occurs with gem minerals. Marble and lapis lazuli are gem rocks formed metamorphically, and rubies, spinels and garnets are gem minerals are often crystallized within rocks that are undergoing metamorphic changes, due to heat and pressure.

[Ruby in metamorphic quartzite rock, lapis lazuli mosaic bust: Images courtesy of Las Vegas Jewelry and Mineral, polished marble "egg" from metamorphosed limestone from Arizona: Image courtesy of www.barlowsrocks.com] ** Check the text: See Lyman, page 38, for a picture of metamorphically created almandine garnets, and page 12 in the Hall book to for kyanite and staurolite in metamorphic schist Just a Few Words About Organics

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Thus far only those originally organic gems that have become fully mineralized through petrifaction, have been referred to in this lesson. Another lesson of equal length could be written about the precise mechanisms by which the various true organic gems come to be. Such coverage is beyond the scope of this course, however; so the following inadequate summary must suffice. (Review the definition of mineral vs organic gems from Lesson One, if necessary). Organic gems are derived from either: 1) The secretory activities of organisms that were living (or recently dead) at the time of the harvest of the gem material. Examples would include pearl, bone, horn, ivory, tortoiseshell and coral. Such secretions might be entirely mineral, as with the calcareous corals, for example, or entirely organic as with tortoise shell, or a combination of both mineral and organic components as with pearl, proteinaceous corals, and ivories.

[Warthog tusk (ivory), Victorian Ivory brooch, 1930's natural tortoise shell brooch, raw black coral branches (proteinaceous type): Image courtesy of Las Vegas Jewelry and Mineral, polished black coral branch pin with Tahitian pearl]

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2) The secretions and structures of organisms long dead which have, over time, undergone geological and/or chemical changes from their original state. Examples include amber, copal, jet, and bog oak. Chemical oxidation or reduction, compression, dehydration, or polymerization, have changed their original properties, but these materials still consist, at least partially, of organic molecules.

[Circa 1880 "bog oak" brooch (a semi-fossilized wood from ancient peat bogs, similar to, and used as a simulant for, jet), amber rough: "Burmite" very rare Burmese variety, noted for its cherry red color, typical Baltic amber] Where Gems are Found and How they are Mined An important distinction must be made between the place where a gem forms, and where it is mined or collected (these two, most often, are not the same). The places where we mine or collect gems are known as gem deposits, and these are classified as either primary or secondary. Primary Deposits: A primary deposit is one in which the sought-after material is still held within the original site of its formation. These "lode" deposits are often located deep underground, and encased in solid rock (pegmatites, veins, pipes, etc.) They are, in general, likely to require substantial monetary outlay in personnel and equipment for recovery. Although metal ores (does the famous Comstock Lode come to mind?), are frequently mined from primary deposits, it is rarer with gemstones. In certain locations, though, diamonds, and colored gemstones can be profitably mined from such sites. Techniques involve either tunneling deep into the Earth, or using open pit technology necessitating removal of massive amounts of "overburden" to get to the deeper gem bearing layer. **Check the web: Get a moving panoramic view of the famous, "Lavender Pit" copper mine in Bisbee, Arizona at this site. This, now abandoned strip mine, 291

named for Harrison Lavender, an executive with Phelps Dodge Company, encompasses 300 acres, is 950 feet deep, and yielded 351 million tons of ore during its active life: http://virtualguidebooks.com/Arizona/CactusCountry/Bisbee/Lavender Pit.html A consideration which is important in this type of gem mining is that the typical blasting and crushing done with metal ore materials can harm fragile gem crystals, so that much of the work must be done by slower and more labor intensive hand work. Sapphires in the US, have been "hard-rock" mined, off and on (depending on economic factors) in Montana, primarily at Yogo Gulch. The deposit there consists of sapphire cyrstals in a lamproite pegmatite dike. Although they are some of the highest quality blue sapphires in the world, lacking color zoning, and possessing an "out of the ground" cornflower blue color that requires no heating, the extreme prices necessary to repay their mining costs, limit their marketability.

[Yogo sapphires: before and after faceting. Yogos are among the most beautiful and expensive in the world: Images courtesy of www.foxfinejewelers.com] ** Check the web: Here's a site with pictures and text showing one of the newest of De Beers' South African diamond mines. It explains some of the steps involved in extracting and processing diamonds, at a recovery rate of approximately one carat of diamond per ton of ore.http://www.miningtechnology.com/projects/de_beers/ Secondary Deposits: Although a primary deposit may have been formed deep in the Earth, uplift, crust folding, or other geologic events can bring it to, or very near, the surface. All exposed surface features are subject to erosion and weathering, and this is true of gem deposits as well. The agents of erosion will then act to release the gems from their primary sites, and they collect in 292

new secondary deposits. Secondary deposits are classed as either eluvial or alluvial depending on their relationship to the original source. Eluvial: When the softer more easily weathering primary structures simply release the harder and tougher gem materials, and the gems can be found at the site of decomposition, the deposit is eluvial. The gems can then be located within the debris, and generally it will be a relatively inexpensive process to gather and remove them. Additionally, the host rocks, which may contain valuable primary deposits can usually be easily located for other types of mining. Eluvial gem rough, although often large in size, tends to be internally fractured, and quite angular and irregular in shape, which can limit its potential as faceting material. The world's largest peridot mine, located on the San Carlos Apache Reservation in Arizona, is an eluvial deposit where the peridot is weathering out of the volcanic basalt primary source.

[Images courtesy of Robert Drummond, www.mtlilygems.com]

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[Arizona peridot eluvial rough, note fractured area and angularity of pieces] Alluvial: More common, and in most cases, more desirable, are alluvial (also known as "placer") deposits. The gems in these have been transported from the original site of their release, usually by water, but also possibly by wind or ice. As most gems are both denser and harder than most rocks, they accumulate on the bottom along with gravel, sand and mud, in eddies and pools in streams, rivers and along coastlines. (They can also be found in sites that had flowing water in the past, but have long since dried up). The abrasive and frictional forces that occur as the gems are moved downstream cause the weakest parts to break off, and the edges to become more smooth and rounded. Alluvial rough, though usually relatively small, is often of high clarity, and superior faceting quality. The longer the distance the rough has traveled, the smaller and more rounded it becomes. Alluvial diamonds are an exception to this rule, in that they are harder than the surrounding rocks, and unless fractured or cleaved retain their original structure and size.

[Australian spinel rough from an alluvial deposit] By far, the greatest amount of economically profitable gem mining is done by exploiting secondary deposits. Techniques range from simple one person panning and screening operations, to large scale dredging and hydraulic washing/sorting by big companies. Food for thought: 294

Question 1: Dealers who supply facetors with gem rough may sometimes tumble it first. Why? Question 2: What type of terrain do you think is most likely to yield eluvial deposits? alluvial ones?

[Alluvial diamond miners in Sierra Leone, a collection of diamond rough from Arkansas, (the largest piece is under one carat) hand dug and screened from an eluvial deposit: Image courtesy of Kevin Jones] **Check the web: Have a look at the Crater of Diamonds State Park in Arkansas where you can dig for diamonds and keep what you find!http://www.craterofdiamondsstatepark.com/

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[Tan Huong, Vietnam, ruby and spinel mine. Back hoes remove about six feet of soil then high pressure water is used to loosen the old buried stream bed so the miners can use screens and sluices: Image courtesy of www.gemsfromearth.com] Within alluvial "gem gravels" several different types of gems may be found together, reflecting the various eroding primary sites within the local drainage area. Tracking back to the primary source of a particular gem ("Mother Lode") is usually very difficult, if not impossible. Answers to the thought exercises for this lesson. (If you don't understand something in these answers it's time to email me and ask!) 1): Gem rough that comes from primary sources or eluvial sources may have internal fractures, partial cleavages, or ungainly shapes. Tumbling the rough simulates what happens as weathered-out gems travel down streambeds, breaking off weak areas and wearing away protrusions. The tumbled rough is more desirable to the facetor as it is cleaner, and better shaped for good recovery; so they will pay more for it. 2): Flat terrain, especially that which is in an area that is arid, is most likely to yield eluvial gems. It is not surprising, then, that we find eluvial peridot at a place named "Peridot Mesa" (mesa = table top). Alluvial gems however, are most likely to be found in the foot hills and valleys of mountain ranges. (Where did the '49ers look for gold nuggets?). You have now completed the web lecture for the tenth lesson! Go back the the course web site to: 1) complete and submit the homework assignment on the text readings and assigned web essays 2) take the nongraded practice quiz on this web lecture 3) post a comment to the discussion board for this lesson, and 4) when it is available, complete the graded quiz based on this web lecture. Now Get Ready for the Final Exam!!

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Chrome Diopside I was prompted to write these comments on chrome diopside after seeing a television shopping network's recent promotion of this gem as "Russian diopside" and their featuring it extensively in rings. Chrome diopside is a rich, emerald green variety of the mineral diopside which derives its color from chromium. A recent Russian find in 1988 is the source of the Tsavoritelike stones that are gaining in popularity and recognition today. As beautiful as the material is, its use in rings is risky at best. A hardness of (5.5-6), moderate brittleness, and cleavability limit its use to pendants, brooches and earrings unless placed in highly protective settings and given gentle treatment. For these other uses, though, the stone is beautiful and under-appreciated. Good cutting is important as this variety, especially in larger sizes, can be very dark. A good cut with fairly shallow angles can improve brilliance. Cabochons can be distinctive and attractive, and collectors eagerly look for the rare cat'seye form. A well cut piece of chrome diopside is a beautiful sight to behold, and a reasonably priced alternative to Tsavorite or chrome tourmaline.

[Chrome diopside gems: emerald step cut, pear shaped cabochons, cat'seye set, pair of heart shaped brilliant cuts]

Value The prime value factor for this gem is color, with medium dark green stones at the top. Such a stone in a larger size (2 cts or more) is especially rare since so many larger pieces suffer from light extinction and are too dark. Cat'seye stones bring a premium price. Fine cutting enhances value considerably by adding scintillation and brilliance. 297

Gemological Data Makeup: a calcium, magnesium silicate Luster: Vitreous Hardness: 5.5-6 Crystal structure: Monoclinic Fracture: conchoidal to uneven Cleavage: perfect in two directions Density: 3.29 RI: 1.66 - 1.72 Birefringence: .029

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Jet If you were to visit some of the many English websites devoted to this gem you would begin to realize, first, what a long history of use the gem has in the British Isles, and in the World, and second, how passionately some individuals feel about this lesser known gemstone. Jet, an opaque black, organic gem is usually described as a form of fossilized wood, but not in the sense of "petrified" wood, where the orginal cellular structure has been replaced by minerals and preserved. Jet is essentially a form of lignite coal, having its origin in buried wood from ancient forests, but much modified over millions of years by compression and heating deep underground. Occasionally you find the term "black amber" applied to jet, but that name is neither geologically nor gemologically accurate and must be considered a misnomer. Perhaps the name arose due to the fact that, like amber, jet will develop a static electrical charge when rubbed. One of the earliest of mankind's ornaments, jet beads have been unearthed from burial sites dating to the Bronze Age. The extension of the Roman Empire into the British Isles resulted in this black gem's use in the jewelry and art objects of rich Romans. Besides ornamental use, there are written records showing that powdered jet was used as a medication by the physicians of the 17th Century. The height of jet popularity was during the Victorian era. Upon her widowhood, Queen Victoria began wearing "mourning jewelry", primarily of jet, and continued to do so throughout her long life. The public emulated their Monarch, so that earrings, brooches and pendants were produced in large quantities and varying qualities and worn by everyone who could afford them. By the 1870s the gem had reached its peak of use and, until quite recently, has been in a consistent decline in its popularity ever since. Some speculate that the gem's association with death, mourning and sadness is responsible. Recently, signs of renewed popularity have been seen, perhaps as part of the general revival of interest in Victorian jewelry, or maybe due to its credentials as a gem with "metaphysical" attritubes and uses.

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[Jet rough, Victorian brooch, rose cut jet cabochon]

[ Victorian jet jewelry: carved bracelet, bead necklace, earrings] Although there are known deposits of jet in many parts of the world, such as the USA (Utah, Colorado, New Mexico), Spain and the Middle East, historically, the premier site is along the Yorkshire coast, near the town of Whitby in England. Deposits there occur in shale beds which form cliffs along the beach and which extend under the sea. During the height of its popularity it was mined, but both before and after that period, a sufficient supply is picked from "land slides" and collected from material washed up on the beaches. Jet is soft (hardness ranging from 2.5 to 4) and somewhat brittle. Jet jewelry shouldn't be cleaned in an ultrasonic or with steam. It can be washed with warm soapy water and a soft brush, and a small amount of mineral oil applied to the surface will revive the shine.

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Simulants such as bog oak, "French Jet" glass, ebony wood, dyed horn, early and modern plastics and a rubber-like material called "vulcanite" are seen in the marketplace. One sure way to verify natural jet is to touch an inconpicuous part of the piece with a red hot needle and smell the results -only jet will smell like burning coal.

Value Factors Even the best quality jet is modestly priced as a raw material. Most of the value of jet is associated with the artistry of carving or the historical context of the jewelry or ornamental piece. The finest pieces have a smooth, well polished surface that is free of cracks and blemishes.

Gemological Properties: Chemical Composition: a mix of hydrocarbons Crystal System: Amorphous RI: 1.64 - 1.68 Density: 1.32 Fluorescence: none Luster: resinous to vitreous Hardness: 2.5 - 4 Fracture: conchoidal Toughness: poor

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Benitoite

Benitoite is the quintessential American gemstone. Gem quality specimens are mined nowhere in the world except in San Benito County, California. Adopted as the California State gemstone, it is a favorite with collectors who admire its beautiful blue body color and its dispersion (.044) equal to diamond. Dispersion has the potential to cause stones to twinkle with flashes of red and green, although there is a trade-off between dispersion and body color. Some admirers are willing to forgo the dispersive display to get a darker blue stone, while others admire a lighter stone in which dispersion is more evident. The stone below shows a balance between visible dispersion and rich blue body color.

[A 2.0 carat stone showing dispersion] At hardness 6.5 it is tough enough for most jewelry applications. Its scarcity, however, makes it virtually unknown to the general public. The flattened triangular crystals are usually small and highly dichroic showing blue and colorless. Obtaining the blue color usually means orienting the crystal for lesser yield. Finished gems are almost always under 1 carat and usually less than .5 carat. No treatments or enhancements are known for Benitoite. It is truly one of the most beautiful (and wearable) of the collector gems.

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[Benitoite gems: varying in hue, tone, and clarity]

Value This gem is quite expensive, especially for rich blue, clean stones at carat and above sizes. Clarity enhances value, especially in stones eyeclean or better. Very light and very dark stones are on the lower end of the value spectrum with medium dark stones at the pinnacle. Perfection of cut is sometimes sacrified, even by the custom cutter, to achieve the largest possible gem so windows and less than optimal proportions are fairly common. Gemological Data Makeup: a barium, titanium silicate Luster: Vitreous Hardness: 6.5 Crystal structure: Hexagonal Fracture: conchoidal Density: 3.67 RI: 1.76-1.80 Birefringence: .047

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Aquamarine Blue to blue-green beryl, known as aquamarine, is quite a familiar stone, a staple in jewelry stores, catalogs and on home shopping programs, and rightly so. It is a magnificent gem which can be stunningly beautiful when well cut and polished and of good size and color. Unfortunately, huge amounts of material have been sold which either lack enough color to truly be called aquamarine or which are inferior in their fashioning. The most common natural color for this gem is a light to medium light slightly to moderately greenish blue. The name, aquamarine, then, indicates its resemblance to the color of sea water. Virtually all rough is heated to convert some of the green tones to blue. The treatment is undetectable and stable and therefore the consumer should assume all pieces to be heated unless otherwise specified. Recently a growing number of consumers have begun to appreciate the natural greenish gems. At hardness 7.5 it makes an acceptable ring stone and requires no special care or precautions in cleaning. The most common types of inclusions found in this variety are liquid filled fingerprints and hollow growth tubes. Major sources of stones include Brazil, Nigeria, Zambia and Madagascar. A common simulant for this gem is light blue synthetic spinel which can easily be distinguished from aqua by its optic character and refractive index. Aquamarine is the birthstone for March.

[Aquamarine gems: varying in color, quality and fashioning style]

Value The deepest blue large stones have the highest value with medium and light blue stones of the same size fetching less. In smaller sizes, price still depends on color which is harder to obtain in small pieces. Blue-green stones of any size have traditionally had only about 50 -75% of the value of true blues, but this is changing as consumers are beginning to favor and seek out 304

unenhanced stones. Mass production of blue topaz by irradiation in the 1980's briefly depressed the aqua market, but it rebounded when topaz took a nose-dive -- chiefly because the supply of darker blue topaz is virtually unlimited whereas only nature can make fine colored aquas which are now, and always have been, rare. Heating doesn't darken the color of aqua it just diminishes the green component. African aquamarine is relatively more abundant and can be less expensive that comparable Brazilian material.

Gemological Data: Makeup: a beryllium aluminum silicate Luster: vitreous Hardness: 7.5 Crystal structure: hexagonal Fracture: conchoidal Cleavage: none Density: 2.69 RI: 1.57-1.58 Dispersion: .014 Birefringence: 0.006 Pleiochroism: weak to moderate: blue and greenish blue in lighter or darker tones

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Rock Crystal Quartz I really had no thought of writing an essay about what I considered the least interesting of the crystalline quartz varieties: rock crystal. That is, until a friend gave me a gift of a beautiful "coffee table" book called Rock Crystal Treasures: From Antiquity to Today. The breathtaking pictures and well researched text served well, to give me a needed "attitude adjustment". The term, rock crystal, in use today, derives from the Greek word "krystallos" meaning - ice. In a treatise written around 300 BCE, Theophrastus (a pupil of Aristotle) explains the origin of rock crystal as being from ice that forms at such a high altitude, and therefore such a cold temperature that it was incapable of melting. This idea held sway until the 17th century when large deposits were located in Brazil, an obviously warm location. Today's major sources are Brazil and Madagascar with important secondary deposits in many other places including Arkansas and New York in the USA.

"Quartz Sceptre" The Greeks were not the first appreciators of this gem, however. Babylonians circa 2000 BCE were advised that owning amulets or seals of rock crystal would increase a man's wealth and possessions. Making collections of rock crystal specimens with what were viewed as metaphysically important inclusions was a pasttime of the wealthy in ancient China. These items, purchased for purposes of contemplation and spiritual enlightenment, were sometimes gained at great price -- as there are records of rich men spending themselves into ruin to obtain the best pieces.

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Included quartzes also have a small share of today's commerce: with over 40 minerals known to occur as inclusions in quartz there are still plenty of specimens for the interested collector.

Rock crystal with inclusions of: tourmaline, pyrtie, edenite Rock crystal balls and skull carvings have long been given special significance in divination and necromancy. These artifacts have an enthusiastic audience in today's world, although cheap glass imitations abound. (By the way, the doubly refractive nature of quartz makes a dual image visible through them, not seen with glass). Early Christian art makes frequent use of rock crystal to symbolize purity, by its association with the Virgin Mary or angelic figures in paintings, tapestries and other art objects. Jewelers from earliest times until today have used rock crystal liberally. Some of the most well known and photographed examples include Edwardian, Art Noveau and Art Deco pieces in museum collections. In today's gem market, the place of rock crystal is a modest one. New facetors often choose it as an inexpensive, yet natural, practice material and carvers appreciate the availability of large, inclusion free pieces.

Carved rock crystal 307

For the last several decades colorless quartz has been made in laboratories for use in communications and electronic equipment. Although colored synthetic quartzes are something to worry about when purchasing amethysts or citrines, natural rock crystal still reigns for gem use, as it is cheaper and more abundant than the man made version.

Value Factors As huge crystals are available, the value of gems or carvings from this material is almost entirely due to the beauty, interest or artistry of the piece.

Gemological Properties: Chemical Composition: SiO2 Crystal System: Trigonal RI: 1.54 - 1.55 Density: 2.65 Fluorescence: none Luster: vitreous Hardness: 7 Fracture: conchoidal Fluorescence: none

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Red Beryl

Discovered in the late 1970's and still found in gem quality at only one site in the world, the Wah-Wah Mountains of Utah, red beryl, or Bixbite, is one of the world's rarest and most desirable gemstones. Typically as included as its fellow-beryl, emerald, few crystals approach gem quality. Most specimens of fine crystals are zealously guarded by mineral collectors and are never faceted. Found in white volcanic rhyolite; its color is contributed by cesium and manganese. Fewer than 10,000 stones are cut per year with more 95% of those being melee, mostly in lower grades. Various commercial mining ventures, in the past, have had sporadic success in producing stones, but a new enterprise, using more modern methods, is doing better. Red beryl remains, though, one of the most expensive of all colored gems. In recent years Russian synthetic red beryl has come on the market.

[Red beryl (Bixbite) gems: One of the rarest] Value Factors The great rarity of this material and its popularity with collectors means that almost any sized piece in any clarity and color grade can find a ready buyer. The best stones would have a raspberry pink to slightly purplish red color and be no more than slightly included. The rule of exponential increase with increase in size decidedly applies to this gem so often found in sub carat sizes. Cut is an afterthought, value-wise, in this material as cutters seek to produce the largest possible gem from their rough so windowed stones with poor proportions are in the majority. Gemological Data: Formula: Be3Al2Si6O18 (+Mn, +Cs) Crystallography: Hexagonal

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Luster: Vitreous Hardness: 7.5 - 8 Cleavage: Indistinct. Fracture: conchoidal to uneven Density: 2.66 - 2.70 RI: 1.58 - 1.59

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Coral Other than shells and animal teeth, coral was one of the earliest jewelry materials enjoyed by our species. Neolithic amulets in red coral found in digs in Switzerland date back to 8000 BCE. Virtually every cilivization since then, which either lived in proximity to warm shallow seas, or had developed trade routes to such, has made enthusiastic use of this material. Living corals are tiny, colonial, filter-feeding invertebrates which manufacture solid living quarters out of calcium carbonate or protein. It is the collective, vacated homes of previous generations upon which the living coral film grows, and which we harvest and make use of in jewelry and carving. Historically the important gem corals have been divided into "calcareous" (stony) and "proteinaceous" (horny) types. At present, with these two traditional sources becoming scarce and demand, especially for inexpensive bead material driving the market, two other types ("sponge", and "bamboo" corals) are commonly seen. When someone describes a lipstick or a flower as "coral" colored, what comes to mind is a slightly orangey medium red. Traditionally this color, which occurs naturally in the calcareous corals, was the standard by which the group was judged. The globally wide-spread calcareous group is made up of species whose colors range from white, pink, and peach to "coral" red. The highly desired, hot, vivid reds come primarily from the Mediterranean and the seas around Japan, and for these specimens the competition is vigorous. They grow as branching structures which look something like a leafless tree, and in the rough, show minute parallel striations on their surface. Although rather soft by gem standards, they are reasonably tough and take a high polish. Natural colors are due to organic carotenoid pigments, but pieces of inferior color are sometimes dyed.

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[Calcareous corals: polished branch, 10x photo showing striations, top color red cabochon]

[Calcareous corals: pink carving, white carving, baby pink beads] The other important group, whose houses are made of a tough, keratin-like protein called conchiolin or gorgonin, comprise the black and golden corals. Although not highly mineralized, the protein is very tough, so that properly prepared and polished pieces are near the equal of the stony types in durability and beauty, and sometimes exceed them in value. Colors range from black to dark brown to golden. The golden color is highly prized and can be natural, the result of injury or degeneration of the black coral organisms, or human-induced by bleaching with hydrogen peroxide. (After all, they are made of a hair-like protein).

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[Proteinaceous corals: Living black coral, polished cabochons, polished branch fragment and bead necklace]

[Proteinaceous coral: polished golden coral branch] The blue and "sponge" corals are calcareous but with a much less compact structure than their pink and red relatives. As a result their texture is rough and porous and they take little, if any, polish. The natural colors are pinkish red with brownish areas, and grey blue, so they are usually dyed to improve their color, and/or resin impregnated to increase their durability.

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[Enhanced red "sponge" coral bead, bead at 10x showing porous structure, at 40x showing resin in openings]

[Enhanced blue coral beads, bead at 15x showing structure] Bamboo coral, or "sea bamboo" has an interesting structure that explains its name. The coral skeletons consist of stretches of branch-like, stony calcium carbonate material, interspersed with joint-like regions of gorgonin protein. The natural color is creamy white with brown or black. Sometimes the harder sections are cut out and dyed to make small beads or cabs, while in other cases larger pieces are used which incorporate both regions and retain the banded patterning.

[Natural bamboo coral branch, dyed bamboo coral beads] Like most other organic materials, fossilization of coral can occur through petrifaction or the creation of pseudomorphs. Fossil corals from ancient colonies which have become silicated, make durable (hardness = 7) and interesting cabochon materials.

[Fossil Coral from Indonesia] In addition to various enhancements, there are coral simulants in the market, such as, dyed shell, and lab creations such as "Gilson Coral" (although not a true synthetic, the composition, appearance and properties 314

are quite close). Less convincing simulants, such as glass and plastic, abound in inexpensive costume jewelry. Coral gems with their hardness of 3 - 4 should be worn and cleaned gently. Warm water and mild detergent are best for cleaning needs, and daily wear rings or bracelets are risky. The calcareous types can be damaged by exposure to acids and the proteinaceous types should be protected from high heat and long exposure to water.

Value Factors By far, the most valuable corals are the natural reds, blacks and golds. Fashions change in this regard, though, as the white and baby pinks were preferred in Victorian times. A good polish and freedom from blemishes is important and, of course, the artistry of the fashioning must be taken into account. Some locales from which corals are obtained have been over-fished or environmentally degraded, leading to protective management of the stocks and scarcity of supply. Happily, in the future it may be possible to "farm" some types of corals to supplement our needs. There are pilot programs attempting this in Japan and Hawaii.

Gemological Data: Varies by species

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Ivory Ivory, as defined by most gemologists, is derived from the teeth or tusks of mammals, although some other materials with similar characteristics and appearance have traditionally been given this name. Examples of tooth ivory are less common, and generally limited to: hippo and sperm whale teeth (teeth are defined as dentition which is not visible when the mouth is closed, whereas a tusk protrudes from the closed mouth). Tusks from African and Asian elephants, wild boars, walruses and narwhals as well as extinct mammoths and mastodons have been used throughout history (and prehistory) to produce a range of ornamental and useful objects. Simple ivory amulets and tools have been found in archeological sites dating 7000 years before present. The Chinese penchant for ivory goes far back in their history (5000 BCE) as does their supremacy in the art of carving it into intricate designs and inlays. By 500 BCE India was engaged in a vigorous ivory export trade. The properties of ivory vary somewhat by species in terms of hardness, uniformity and the basic shape of the raw material. Some sources, like elephant tusk, provide large, mostly solid pieces, whereas other types (like narwhal tusks) are mostly hollow, and others like hippo teeth are smaller, which can limit useage to certain sizes or shapes. The hardest and whitest ivory is derived from hippo teeth which makes them more difficult to carve, but less likely to stain and crack. ELEPHANT IVORY The majority of very old ivory carvings and ornaments are probably from Asian elephants whose tusks are relatively smaller and found only on male animals. Within the last several hundred years, however, the African elephant has been the ivory provider of choice, due to its historically greater population numbers, larger tusks, and the fact that both sexes are tusked. The once thriving commerce in African elephant ivory would stagger today's conservation minded individual -- before plastics were invented in the late 19th century, ivory was the source for such diverse and universal items as buttons, hair combs, jewelry, furniture inlay, billiard balls and veneer for piano keys. (The finest billiard ball makers produced only three balls per tusk). By the 1970's when the environmental movement swept the Western world, the consequences of this carnage were obvious. In 1989 a world-wide ban on 316

elephant ivory trade was instituted as part of CITES (Convention on the International Trade in Endangered Species). This treaty has had mixed, mostly positive, results, with elephant populations rebounding to a degree, and interest in still-legal forms of ivory and ivory simulants increasing. The down-side is the inevitable escalation of value of elephant ivory objects, and consequent stimulation of black market trade. Currently small parcels of CITES approved ivory from elephants dying of natural causes or captured goods from smugglers are legally sold to finance conservation efforts.

[19th century Chinese dice cup and Victorian needle case, Victorian Era brooch, Contemporary legal elephant ivory scrimshaw pendant] "FOSSIL" ELEPHANT IVORY Until about 7-10,000 years ago, mammoths ranged over Eurasia and mastodons over the Americas. Throughout their long reign as species, innumerable individuals died and were buried in mud, ice or peat. These artifacts, although not mineralized in the true sense of fossilization, have been preserved, and due to erosion, geological events or mining have been, and are being, unearthed and used as ivory sources. Like all elephant ivories these show distinct structural properties which result in a layered structure in longitudinal section and a cross hatched 317

pattern in cross section. This characteristic called the "engine turned" effect is diagnostic of elephantine ivories and absent in all other forms. These ancient ivories sometimes have acquired unusual colors through long contact with minerals and mineral solutions. Such materials are not covered by CITES, indeed the species are already extinct, and are becoming very popular. In the US, digging for anything on public lands is restricted by Federal land management agencies, but in Alaska, Canada, Greenland and Siberia, Inuits and other native peoples have been greatly benefited by the ability to harvest, fashion, and trade these items to an eager world market.

[Contemporary mammoth ivory amulet, mammoth ivory showing "engine turned" effect, mastodon ivory ojime bead (19th century Japanese)] MARINE MAMMAL IVORY Marine mammals, particularly walruses, and toothed whales (sperm whales and orcas) have been a long treasured source of ivory for populations in locations where these species are common. Inuits, in fact have a much longer history of walrus ivory use than that of the much harder to kill whales. Marine mammals are protected from harvest, except for quotas for certain native peoples who have the right to use their legal catches for meat, hide, bone and ivory and the right to fashion and sell such artifacts. This represents a welcome economic benefit for such groups, as well as a valuable stimulus to preservation of ancestral arts and crafts. Walruses being at least semi-terrestrial animals have also been long buried and recently unearthed -- such "fossil" walrus ivory can also be legally collected and traded by indigenous peoples. In structure walrus ivory shows a distinct core region when sliced in cross section.

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[Contemporary legal walrus ivory bead, "fossil"walrus tusk slice showing mineral staining and central core] Sperm whale teeth have a long history of use in New England in the USA, and throughout the whaling nations of the world. The most common way the teeth were fashioned was by leaving them whole or taking small sections and decorating the piece with an engraved and colored design, called scrimshaw. Most often the designs were related to nautical or whaling subjects.

[Sperm whale tooth scrimshaw: Image courtesy of Booth Trading Company] OTHER IVORIES At present hippos are not considered endangered and are not covered by CITES. They shed teeth naturally which people located in their habitats can collect and legally sell to much of the world (the US, UK and most European countries, however, do not allow any "raw" ivory to be imported, regardless of source). There is a huge market in Japan and China, though, where small carved objects of hippo ivory have largely replaced those of elephant ivory.

[Antique whole hippo tusk carving: Image courtesty of Dr. Terrill Smith, contemporary Japanese hippo ivory netsuke] 319

During the Victorian Era many gems of organic origin were in favor, including obscure ivories such as seen in this circa 1870 brooch fashioned of two animal (pig?) teeth.

[Victorian animal tooth brooch] Although most would define ivory as deriving from mammal teeth, one notable exception is the case of hornbill "ivory". Technically the material is more akin to horn than tooth as it derives from the "casque" or second beak which grows on top of the regular beak in this group of souteastern Asian birds. It is a golden color and exceptionally translucent with the most coveted and expensive specimens showing a bright red "rim". These birds are endangered and cannot be legally hunted, nor can items from them be traded except under restricted conditions as certifed antiques in some parts of the world.

[Kenyalang "Helmeted Hornbill": Image courtesy of Sarawktourism.com, antique hornbill ivory netsuke] IVORY SIMULANTS/ENHANCEMENTS With the current restrictions on ivory trade in place, we can easily understand the emphasis on simulants in today's market, but simulation of ivory is nothing new. Ivory has always been an expensive, limited, and much imitated material. Two natural materials which have a long histories of use as substitutes, are bone and "vegetable ivory" derived from tagua (S. America) or doum palm (Africa) nuts. Early plastics such as celluloid and casein were widely popular as faux ivory from the late 19th century, with modern plastics carrying on the tradition today. 320

Simulants can be detected relatively easily by microscopic examination. Plastics and vegetable ivory show a complete lack of the "structure" typical of ivories. Bone, although showing internal patterns that verify its origin as an animal tissue, is quite distinctive with its Haversian Canals.

[Contemporary bone necklace, early 20th century celluloid brooch, contemporary tagua nut carving] Relatively little in the way of enhancement is used on ivory, the most common being the staining of newly carved items with tobacco juice, tea or other dyes to simulate the appearance of great age. Similar effects can be obtained with gentle heat or irradiation. Mild bleaching solutions of hydrogen peroxide or chlorine can even out color, and remove some blemishes, and is occasionally done. Very rarely specimens of bone or ivory are dyed blue with copper salts to simulate a rare, naturally colored, fossil ivory known as odontolite. CARE As a soft organic gem, ivory deserves gentle cleaning and careful use. Wiping the piece with a damp cloth should suffice for most cleaning needs and prolonged exposure to high temperatures should be avoided. Value Factors Because important legal and ethical factors restrict and influence the market for ivory, it is difficult to generalize about value. Clearly, antique ivory objects, under conditions where they can be legally traded, are valued based on the rarity of the materials, their age, provenance, and the artistry of their fashioning. Examples of items for which collectors (ethical and otherwise)

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will pay dearly are large elephant ivory pieces, narwhal tusk work, and most precious of all, hornbill "ivory" carvings. In the arena of legally traded ivories and ivory simulants, most items are modestly priced with rarer and larger items and those with greater antiquity or higher artistic merit at the top, and vegetable ivory, bone, and plastic simulants in the lower brackets. "Fossil" ivories which have been stained attractive colors through natural mineral processes do bring a premium price. In any ivory piece, translucence and freedom from cracks is valued. Yellowish, orangey and brownish hues (unless they are deliberately applied to simulate age) add value as a patina. Gemological Properties (These vary somewhat with species, the ones below are for elephant ivory) Makeup: 65-70% hydroxyapatite Ca5(Po4)3OH, plus collagen and elastin protiens Crystal system: none, amorphous Refractive Index: 1.54 Hardness: 2.5 - 2.75 Toughness: fair Specific Gravity: 1.70 - 2.0 Cleavage: none Fracture: splintery UV Reaction: fluoresces weakly to strongly bluish white to LW, less to SW Luster: greasy

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Danburite First discovered in Danbury, Connecticut, in 1839, this gem has been found and mined in Japan, Russia, Mexico, Burma, and Madagascar. It ranges from milky translucent white, to transparent pieces of colorless, light yellow, tan, and rarely, very pale pink. The type locality of the US deposit which was named for the town nearby, has long since been covered over, and made inaccessible by the growth of this now rather large community. Pieces that actually originated from this location are now prized by collectors. Danburite is found in metamorphosed limestones and low temperature hydrothermal veins, but few its numerous locales yield either impressive crystals for the mineral collector, or transparent pieces of sufficient size to facet. Joel Arem in his "Color Encyclopedia of Gemstones" states that although the mineral itself is relatively common, large, facetable pieces are rare. The crystals often have a distinctive wedge-shaped habit and nicely terminated ones are beautiful to see. The best crystals, mostly translucent or milky white have historically come from mines in Central Mexico. Although similar in shape and color to topaz crystals, Danburite can be distinguished by its lack of cleavage compared to the strong cleavage seen in topaz.

[A fine, transparent, orthorhombic Danburite crystal, set with a pink sapphire and a brown diamond, in a silver and 18k gold necklace] Likewise, cut gems have a luster and refractive index very close to that of white, yellow and brown topaz, but gemologically these two species can be separated by the difference in specific gravity (topaz is denser) and birefringence, which is higher in topaz. The distinctive blue fluorescence of many Danburites when exposed to ultraviolet light, is also an indentification criterion.

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[Sawn pieces of Danburite rough from Mexico, some of the crystal faces can be seen] Although it is not common enough to become a major commercial jewelry stone, there is enough material for gem collectors, and adventurous jewelry lovers to bring this lovely and under appreciated gem into their collections. Danburite is also sought out by those who are interested in the metaphysical properties ascribed to gems and crystals.

[Faceted Danburites from various locales, showing the brilliance and luster typical of well cut stones] With no cleavage, good toughness and a hardness of 7; Danburite makes an excellent jewelry stone, that surpasses quartz and beryl in brilliance. Its modest dispersion means that although very brilliant, cut gems lack "fire"(spectral color flecks). Due to some heat sensitivity (the heat from a jewelers torch will fuse it), it is best not to subject this gem to steam cleaning, but otherwise, it requires no special care, and can be used in all applications, including rings and bracelets. There are no known enhancements, synthetics or imitations on the market. 324

Value Factors The tried and true value factors for gems in general apply to this species very well. All other things being equal, larger, cleaner, and better cut stones are worth more per carat. The only caveat here, might be that a noticeably pink stone (most as so pale as to be essentially colorless) would surpass the colorless, yellows, and browns in value. In my opinion, for a relatively rare, brilliant, and quite wearable gem, prices are low enough to represent a real gem bargain.

Gemological Properties: Makeup: Calcium Borosilicate: CaB2(SiO4)2 Hardness: 7 Birefringence: .006 Dispersion: .016 Toughness: good Crystal System: Orthorhombic Luster: vitreous Density: 3.00 Pleochroism: none RI: 1.63-1.64 Cleavage: none Fluorescence: Frequently shows a strong light blue to blue green to LW UV and a weaker reaction to SW UV

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Labradorite Feldspar The Feldspar Group Feldspar is a ubiquitous mineral that, usually in the form of small grains, makes up 50-60% of the content of the rocks of the Earth's crust. More precisely, it's agroup of related mineral species, which, in larger deposits of single crystal forms, are known as several familiar gemstones: amazonite, moonstone, sunstone, orthoclase and labradorite. The entire feldspar group is divided into two main branches, the potassium feldspars: microcline and orthoclase, and the sodium/calcium feldspars known as the plagioclase "series". A solid solution series, in mineralogical terms, is a set of mineral species which grade in composition, within the same basic chemical formula, through mixtures, from one pure end material to the other. In the case of the plagioclase feldspars the series runs from 100% albite (NaAlSi3O8) to 100% anorthite (CaAl2Si2O8) with labradorite in the near 50/50 range. Labradorite Labradorite is translucent to opaque with light to dark grey body color, often with needle-like inclusions of black magnetite or ilmenite and usually showing some fracturing. This gem is the only species that can claim sole possession of an entire optical phenomenon, in this case "Labradorescence". Only Labradorite gems show this distinctive directionally-oriented surface display of one or more metallic looking spectral colors. The structural cause is the repeated thin layer (lamellar) twinning of its crystals which creates both diffraction and interference as light passes through and reflects from the parallel surfaces. One of the most singular aspects of this iridescence is its distinct directionality. Notice in the photo below, how certain faces show a silvery or blue "shiller" and the others do not. Any gem fashioned from this material must be carefully oriented so that this display shows to best advantage, and even then, it will be visible only at certain angles. The thickness and uniformity of the layers determines the color(s) to be seen.

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[Labradorite rough] The name derives from the original mine site along the coast of Labrador, found at the beginning of the 19th Century and which is still productive, but India, Scandinavia, Madagascar and the US now provide additional supplies. The majority of specimens of this gem show a silvery blue to bright blue sheen. The three specimens below show the range from semitransparency, through translucence to opacity seen in the species. Lapidary artists have long exploited the beauty of the material in cabochons and gem carvings. Faceted specimens, though rarely seen, have a distinctive and unusual beauty.

[Labradorite gems] Truth in Marketing There are no synthetics or simulants to worry about with this gem group and enhancements are rarely encounted. One related issue does bear mentioning however--> large quantities of a translucent white Labradorite which originates in India is widely sold under the misnomer "rainbow moonstone" at very modest prices. (True moonstone is a different, rarer and considerably more expensive, species of feldspar that has its own distinctive optical phenomenon.) As you can see, the material in question is no less attractive for bearing its improper name.

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[White Indian Labradorite, aka "rainbow moonstone"] Spectrolite A particularly colorful deposit of Labradorite was discovered in Finland, and later mined elsewhere in Scandinavia, which shows not only blue, but green, gold and rarely red or violet sheen, and has been given its own variety name: "spectrolite", due to its resemblance to the color spectrum.

[Spectrolite cabochon and carving]

[Spectrolite jewelry] Care and Use Due to its modest hardness (6 - 6.5), heat sensitivity, and cleavability this gem is relatively fragile and must be set, worn, and cleaned with care. That care will reward the owner many times over, however, as a high quality, well cut piece of labradorite or spectrolite is a joy to behold. Every movement 328

creates a shifting pattern of surface colors, the brightest of which can rival those on the wings of tropical butterflies. Ultrasonic or steam cleaning is too risky and gems to be used in rings or bracelets should be given protective settings and worn infrequently. The best use for this gem is earrings, brooches and pendants which are worry free. Value Labradorite is a gem bargain, as even the highest quality specimens are a fraction of the cost of comparably colored ammolites, precious opals or fire agates. The most valuable pieces of both labradorite and spectrolite are those with the brightest and most uniform color flashes, showing no "dead" areas. In premium gems the fracturing and inclusions are minimal and nonintrusive. Beyond that, the value of a piece lies in its size and in the artistry of the cutting or carving.

Gemological Properties Makeup: An aluminum silicate: 30-50% Albite (NaAlSi3O8) and 70 - 50 % Anorthite (CaAl2Si2O8) Crystal system: Triclinic Refractive Index: 1.55 - 1.57 Birefringence: .009 Hardness: 6 - 6.5 Toughness: Poor Specific Gravity: 2.70 - 2.75 Cleavage: Perfect in one direction, good in another (at right angles to each other) Fracture: Uneven to splintery UV Reaction: Usually inert Luster: Vitreous

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Mexican Opal There are so many different names in use for this type of opal: fire opal, jelly opal, crystal opal, cherry opal, girasol, etc. In my opinion, therefore, the best general term for this sort of transparent opal with body color ranging from colorless through yellow to orange to deep red and usually without play of color, is Mexican opal. Even though some pieces originate from other locales such as the USA and Brazil. This terminology helps prevent confusion from the term "fire" which is often used to mean "play of color". Mexican opal that does have play of color is in its own small sub-category, and is properly referred to as "precious Mexican opal". All opals are hydrated silicates usually containing from 3 - 10% water; but stones from a few sources (notably Virgin Valley, Nevada) can be as high as 20% in water content. If play of color is present, its source is the same in Mexican opal as for the precious white and black opals. Namely, diffraction and interference of light rays which travel through the spaces between the tightly packed silica spheres of which it is made. Some pieces show their color play in reflected light (more common) and some, only in transmitted light. These latter stones, called "contra-luz" are quite rare and desirable. Facetors appreciate Mexican opal's ready availability in nice sized pieces, its reasonable price, and its wonderful range of highly saturated colors. Only the most transparent pieces lack the phenomenon of "opalescence", which is a slightly to moderately strong milky haze within the stone's interior, similar to that seen in rose quartz. Much has been said about this gem's tendency to craze, that is, to develop fine cracks due to dehydration, but the vast majority of the pieces on the market are stable. Reputable rough dealers screen out the unstable pieces, before sale, by subjecting them to prolonged high temperature and low humidity conditions. Naturally, as with all types of opal, stones are somewhat fragile, and not well suited for use in rings meant for hard everyday wear or in bracelets or cufflinks. Likewise, strong chemicals, ultrasonic vibrations, and abrupt dramatic temperature changes can cause damage. In earrings, pendants, tie pins, brooches and special occasion rings and with reasonable care, it does very well. Cleaning with a soft brush and warm soapy water is safe and effective. It is not advisable, in fact, it is likely to be harmful, to store opals in mineral oil or or glycerin and this practice will not prevent crazing. Storage in water, although safe, has no protective benefit. It is wise, however, to store the 330

stones and jewelry items in their own separate compartments to prevent scratching from harder gems and metals.

[Typical Mexican opals showing a variety of body colors]

[Precious Mexican opal, cat'seye Mexican opal]

[Bi-colored Mexican opal, contra-luz Mexican opal]

Value The most desirable pieces are nearly completely transparent and, when colored, show a strong, highly saturated hue. Most reds in this variety are tinged with various degrees of orange, so pure, spectral red pieces are exceedingly rare and therefore higher priced. Play of color enhances the value of any stone dramatically. Cat'seyes and bi-colored stones also sell at a premium. Mexican opal commands its highest prices in Germany and in Japan where many of the Mexican stones are exported. Here in the US, it remains an excellent bargain, even in larger, custom cut pieces of finest color. Enhancements such as heating, filling or irradiation are at present unknown in this variety. 331

Gemological Data Makeup: hydrated silicon dioxide Luster: vitreous to resinous Hardness: 5.5 - 6 Crystal structure: none, it is amorphous Fracture: conchoidal to uneven Cleavage: none Density: 2.15 RI: 1.42 - 1.43 Birefringence: none

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Chrysocolla Chalcedony The common mineral quartz, occurs both in the familiar single crystal varieties of amethyst, citrine, rose quartz, etc, and also in a number of aggregate forms. These aggregates, such as agate, jasper, and chalcedony, are made up of submicroscopic quartz crystals intermeshed together. When the quartz aggregates are translucent, and of a single color, they are known as chalcedonies. Examples of well known types of chalcedony are brown to orange carnelian, and apple green chrysoprase. Less common, and more valuable, is a type of chalcedony with vivid greenish blue color, frequently referred to as "gem silica" in the trade. More correctly it would be called chrysocolla chalcedony. Structurally it is composed of near colorless chalcedony that has been stained, on a microscopic level, by infiltration of solutions carrying the same copper salts which give color to the mineral chrysocolla. If it is evenly stained throughout, it has an intense, uniform, slightly to moderately greenish blue color. Chrysocolla itself, though beautifully colored, is far too soft and fragile (H = 2 - 4) to be useable for jewelry purposes. Additionally, pieces of pure chrysocolla generally have a chalky, crumbly texture, or occur as thin powdery crusts on the surface of a rock.

[Chrysocolla specimen: lovely but not recommended for jewelry use] The so-called, "gem silica", however, since it is actually a type of chalcedony with quartz's hardness of 7, and excellent toughness, is quite suitable for jewelry use. Sources include, Arizona, New Mexico, Mexico, Taiwan and the Philippines. Rarely, gem silica occurs in botryoidal (with a bubble-textured surface) or drusy (with a sugar-like crystal coating) form.

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[Chrysocolla chalcedony (aka "gem silica"): top quality cabochon, drusy cabochon in a pendant, botryoidal cabochon, carving]

Value The most valuable specimens of this kind of material are those that are highly translucent, evenly colored, free from inclusions, and strongly saturated in color. People who may not realize the rarity of such stones, are, sometimes, taken aback by the relatively high price for what is afterall, a form of quartz, and a cabochon stone to boot. Highly translucent cabochons of the most vivid color may retail for as much as $100/ct. Increased demand and familiarity with this gem has been occasioned by top gem carvers and goldsmiths recently making this stone a "gem of choice". There has also been intense interest by Oriental collectors which has driven prices up as well. Those specimens which tend to greenish hues and which are opaque, included, or uneven in color are much less costly. Gemological Data: Makeup: microcrystalline or cryptocrystalline quartz, Si02, colored by copper Luster: vitreous Hardness: 7 Crystal structure: hexagonal

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Fracture: conchoidal to granular Cleavage: none Density: 2.60 RI: 1.54 Birefringence: 0.004, usually not detectable Pleiochroism: none

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Morganite Morganite is beryl colored by manganese impurities. Although violet and peach are possible colors, the most common and preferred color is pink. Heat and light will remove the yellow component from peach beryl so it is often heated to get "pinker" stones. It entered the American market in 1911 when Tiffany & Co. introduced it and named it in honor of J.P. Morgan. Original deposits from Madagascar are now worked out, but Brazil, Namibia and other locations produce rough. Growth tubes are a typical inclusion in beryl and often seen in Morganite. Very often near colorless specimens are offered as Morganite when they more properly should be labeled Goshenite (colorless beryl). Although it takes a larger stone to develop really good body color, smaller stones can be very brilliant. Like most beryls, Morganite makes an excellent jewelry stone requiring no special care.

[Morganite gems]

Value Medium light to medium pink, clean stones with custom cuts are the most valuable. Very light and included stones are on the lower end of the value spectrum. As Morganite frequently occurs in larger crystals, there is not the exponential increase in price with size we see in so many gems. Paradoxically, smaller Morganites (if they show good color) can be more 336

valuable than larger ones which often, in order show good color must be so large as to limit their reasonable use in jewelry. As is the case with aquamarine, there is a small but growing segment of collectors who prefer the unheated peachy color and are willing to pay a premium to get an untreated piece. Gemological Data Makeup: a beryllium, aluminum silcate Luster: Vitreous Hardness: 7.5 Crystal structure: Hexagonal Fracture: conchoidal Density: 2.80 RI: 1.58 - 1.59 Birefringence: .008

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CHAROITE Named for the only locale in which it is found, the Charo River Valley in the former Soviet Union, Charoite is one of the few gems that is so distinctive in its color and patterns that a gemologist can feel justified in making a "sight" identification. There's really no other material likely to be mistaken for it -at least this is true until a synthetic or man-made simulant comes along some day. Like lapis lazuli, the gemstone that we call "Charoite" is actually a rock composed of several minerals including Charoite! Unlike lapis, though, it is usually nearly pure Charoite mineral, with only slight amounts of microcline feldspar, aergirine-augite and tinaksite. It is the mineral Charoite that gives this gem its unmistakable purple color which, often in the same piece, ranges from very light to medium dark purple and from translucent to opaque. The other distinctive aspect of its appearance is the swirling patterns that form due to its fibrous crystals being arrayed in complex interlocking patterns. First found, 325 miles North of the tip of Lake Baikal, in the 1940's and locally called "lilac stone", this gem was introduced to the Western gemstone marketplace as Charoite in the 1970's. It immediately made a large impact, both with traditional lapidaries and marketers who used it for decorative objects, carvings and cabochons, and, soon after, with metaphysical gem enthusiasts for whom it embodies a long list of healing and spiritual attributes. Charoite is formed from limestone by the process of contact metamorphism. Since this is a relatively common geologic phenomenon it is not completely clear why its distribution is so limited. Apparently the particular limestone in that area had unique chemical properties as did the intrusive rocks. So far, gemologists have not been able to ascertain the exact chemical or structural reason for its purple color. To say that the mineral Charoite is a silicate of complex compostion an understatement: one mineralogical source describes it as a hydrated potassium, sodium, calcium, barium, strontium, silicate hydroxyfluoride! As a gem it is reasonably tough with a hardness between 5 and 6 and no cleavage. Use in rings or bracelets is probably unwise, but most other jewelry uses are safe. It is somewhat heat sensitive, so steam cleaning should be avoided, as should ultrasonic processes. As with the majority of gems, the best cleaning tool is a soft brush, a mild detergent and warm water. 338

One of the loveliest aspects of the best Charoite gems is a slight to moderate chatoyance which gives it a silky or pearly luster. This attribute, as well as the swirling patterns and distinctive purple color, is well demonstrated by the pieces below:

[Charoite gems showing their characteristic color and chatoyance] VALUE FACTORS: Charoite is a gemstone bargain. Even the highest quality pieces are, at most, a few dollars a carat. Look for a lovely pattern, pleasing colors, a good polish and a shape that appeals to you, and you cannot go wrong. If the piece shows some chatoyance, that would add to its value GEMOLOGICAL DATA: Makeup: A rock composed mainly of the complex silicate mineral Charoite Crystal System: Monoclinic Hardness: 5 - 6 Density: 2.5 - 2.8 Refractive Index: 1.55 - 1.56 Birefringence: .009 Fluorescence: LW, weak to inert; SW, weak to inert Fracture: conchcoidal to splintery Luster: vitreous to pearly or silky

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Tsavorite Garnet

Tsavorite, or transparent, green grossular garnet, was discovered in Kenya in the 1960's and given its trade name by Tiffany marketers based on the proximity of Tsavo National Park to the mine sites. It is one of the most sought after and valuable types of garnet. The geologic deposits in which it is found are difficult and expensive to mine and unpredictable in distribution so production as been sporadic. Political conflicts and trade issues further endanger the reliable supply. The crystals which are found show evidence of being affected by tremendous geologic forces, and as a result are seldom found large and clean. Cut specimens over 3 carats are exceedingly rare. The color ranges from lime green to emerald green to pure spectral green and is caused by high vanadium content. Rarely found better than eyeclean, typical inclusions are straight or angular corrosion growth tubes, fingerprints, feathers, veils and graphite inclusions. Like all types of garnet this stone is the birthstone for the month of January.

[Tsavorite gems: brilliant cut trillion, cabochon, step cut emerald cut, marquis brilliants in a ring]

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Given the rarity, popularity, and sporadic supply of these stones, the overall trend in value since their introduction has been up, up, up. The best specimens are those that are pure spectral green in a medium dark to medium tone. Those that are darker or lighter than this are much less desirable. Price exponentially increases with size and a custom cut adds considerable value as the majority of specimens are native cut.

Gemological Data Makeup: a calcium aluminum silicate Crystal system: Cubic Luster: Vitreous Cleavage: none Hardness: 7 Fracture: conchcoidal to uneven Density: 3.61 RI: 1.74 Dispersion: .028

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Moldavite Moldavite is a transparent to translucent olive to bottle green variety of tektite, first found in 1787 at the Moldau River in Czechoslovakia. In general, tektites are natural glasses which are thought to have been created by melting of silica sand or rock by meteoric impact. A popular idea is that the melted material then was flung into the air and cooled into glass as it landed over the area of the impact site. It has also been suggested that they may be of extra-terrestrial origin and that they melted into their glassy state due to high temperatures generated during travel through the Earth's atmosphere.

[Moldavite rough specimen, 10x view of bubbled and crater-marked surface] Iron is the coloring agent responsible for the green color which is diagnostic of Moldavite. Brown, black and yellow tektites are found in other locales. Typical inclusions are bubbles and swirls. The most common cuts that are seen are simple round or emerald facet cuts and occasionally small cabochons. The rough is often available in flattened disc-like or dish-like pieces with very rough edges, that seem to support the melt-splash formation hypothesis. Such pieces are sometimes carved into fanciful shapes and can be very lovely. There have been occasional reports of simulated Moldavite (man-made glass), but those pieces that I've seen are quite obvious, as they are the intense color of old "7UP" bottles rather than the much more muted green of the natural material. As all glasses are, Moldavite is a rather fragile gemstone and should treated with care and restricted to use in jewelry that doesn't receive hard wear.

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[Moldavite: cabochon, faceted gem, faceted in gem in jewelry, carving]

Value Moldavite is cut primarily as a curiosity, and for collectors, although the recent interest in metaphysical properties of stones has substantially boosted its popularity and availability. Poorly cut and polished stones look very dull next to custom cut and polished specimens which are well worth their higher prices which are still quite modest as collector gems go. Gemological Data: Makeup: Mostly Silicon Dioxide Luster: Vitreous Hardness: 5 Crystal structure: Amorphous Fracture: conchoidal Cleavage: none Density: 2.40 343

RI: 1.48-1.51 Birefringence: none Pleochroism: none

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Drusy Gems The word "druse" refers to a rock surface (usually a cavity) covered with tiny individual crystals, such as are found inside geodes or in larger pockets of mineral deposits. Gem minerals which exhibit this feature are said to have a drusy crystal "habit". Until about 10 years ago, drusy minerals were little more than a curiosity, of interest to serious mineralogists, but unnoticed by jewelry designers, gem collectors, and the general public. Times have changed! Drusy materials, at first slowly, then with increasing frequency appeared in the work of noted gem carvers and jewelry designers and, as a result, gained space in gem and jewelry publications.

[Drusy quartz gem carvings] By far the most commonly found drusy is quartz (agate or chalcedony), but many other species can exist in this form. A non-exhaustive internet search yielded the following types: chrysocolla, uvarovite garnet, rainbow pyrite, rainbow hematite, psilomelane, cobalto-calcite, calcite, dolomite, sphalerite, melanite garnet, demantoid garnet, azurite, dioptase, siderite, vanadinite and turquoise. There was even a notation about a drusy pocket found in an iron meteorite!

[Rarities: drusy azurite, vanadinite, melanite garnet] The appeal of drusy material is easy to understand with its multitude of tiny crystals providing a reflective surface reminiscent of sugar or snow. 345

Most non-quartz species of drusy gems, even those with vivid colors like hot pink (cobalto-calcite), day glow green (uvarovite), or multi-color (rainbow pyrite ) are natural.

[Natural color drusies: cobalto-calcite, rainbow pyrite, uvarovite garnet] Naturally colored quartz drusy is found almost exclusively in muted colors such as white, grey, tan and cream. Many quartz pieces, though, are dyed black or other vivid colors such as purple, red, green and blue, and some are coated with titanium or other metallic vapor which creates various iridescent finishes.

[Dyed quartz drusies, titanium coated quartz drusy] The toughness of each drusy piece depends on the nature of the crystals themselves and the matrix to which they are bound. For example, quartz drusy is relatively durable while calcite drusy is fragile. Any drusy is probably more fragile than a single crystal of that same gem, as in addition to the usual worry of scratching or breaking, there is detachment of the tiny crystals from the matrix to be concerned about. All drusies should be treated with some care: use them for pendants, brooches and earrings, but avoid use in rings or bracelets. Clean with a soft brush and soap rather than ultrasonics or steam. With these simple precautions drusy pieces can make a wonderful addition to your gem or jewelry collection.

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In drusy gemstones, the size and evenness of crystal coverage are important determinants of quality. It could even be said that in addition to the usual 4 C's (color, cut, clarity and carat weight) of gem quality there is a 5th C: "coverage". The evenness with which the matrix is covered is a strong value point. Good drusies are relatively rare, especially in non-quartz species.

Gemological Properties: Depends on the species: the information below is for quartz Makeup: Silicon Dioxide Hardness: 7 Dispersion: .013 Toughness: Good (less so for drusy, than single crystals) Crystal System: Trigonal Luster: Vitreous Density: 2.65 RI: 1.54 - 1.55 Cleavage: none

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Fire Agate My appreciation for fire agate has taken time to reach its current very high level. Most of the pieces I saw early-on were poorly fashioned and of low quality, and frankly, I wasn't impressed. Since beginning my serious study of gems, however; I've had the opportunity to see some outstanding specimens and as a result, my enthusiasm has increased dramatically. Fire agate is a brown, microcrystalline quartz (chalcedony) which has a botryoidal (grape-like) growth form, and which contains layers of plate-like crystals of iron oxide (limonite) in various planes within it. The iridescent colors of red, gold, green and rarely, blue-violet, result from interference between diffracted light rays traveling through and reflecting off of these thin layers. (We see the same effect when looking at the rainbow colors at the surface of an oily puddle of water; or in the "orient" created by the layers of nacre on the surface of pearl.) Usually, fire agate pockets occur within specimens of colorless, white or light grey chalcedony. Fire agate is found only in the US Southwest and Mexico and wasn't brought into commerce until after World War II. This, combined with the fact that it's one of the most difficult opaque materials to cut properly, keeps it scarce and mostly unknown to the general public. In order to best reveal the colors, the overlying layers of chalcedony must be very carefully removed from the botryoidal surface creating a freeform shape with a carved upper surface. Just a tiny bit too much material removed kills the iridescence and too much left on dulls it. Such painstaking treatment requires substantially more time per piece by the lapidary, and tends to elevate cost. This type of fashioning also leads to a lack of calibrated pieces and has prevented the use of this gem in mass produced jewelry items. Good fire agates are as impressive in their color display as fine black opal, but far less expensive. Additionally, fire agate is as hard and durable as any aggregate quartz making it wonderful for jewelry uses, including rings. The colors and form are rich and dramatic and generally appeal strongly to men (although I can personally attest to its appeal to women!)

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[Fire agate gems and jewelry]

Value The most desirable pieces show color over the entire surface with no "dead" spots. Red color is generally the most highly valued, but the few pieces with some lavender-blue are also highly sought after. The pattern of colors can be a value factor too. Similar to what is seen in opal, the colors can be tiny dots "pin fire", large blotches "harlequin" or, rarely, have a distinctive pattern such as circles or stripes. Well cut, carved and polished pieces with an attractive freeform outline are more valuable than those produced with a smooth crown and a standard cabochon shape. Gemological Data Makeup: silicon dioxide Luster: vitreous Hardness: 7 Crystal structure: trigonal Fracture: conchoidal to granular Cleavage: none 349

Density: 2.61 RI: 1.53-54 Birefringence: 0.004

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Nephrite Jade Although "jade" has been in use for a variety of utilitarian and artistic purposes for over 7000 years, it was only in 1863 that a gemological distinction was made between the two different species commonly given this name. Jadeite, an aggregate of granular pyroxenes, actually is not related to nephrite, an aggregate of fibrous amphiboles. The fact that they occur in the same color and translucency range, are both incredibly tough, and were traditionally used for the same purposes, along with their superficially similar appearance has led to the odd consequence of having two quite different gems with the same name. Even though marketers, jewelers and the public continue to refer to both gems as jade, more properly the species should be used as, or at least included in, the name: so either nephrite (or nephrite jade) or jadeite (or jadeite jade) is the preferred terminology. Nephrite is, then, a calcium-magnesium silicate that varies from translucent to opaque, and from shades of green, through browns and yellows to greys and near whites as it varies in the proportion of the amphibole minerals in its makeup. The darker pieces are mostly made up of iron rich (up to 5% iron content) actinolites, the lighter pieces contain more of the magnesium rich tremolites. Pieces may be mottled or banded in color, and black inclusions are common. Typically the iron induced green colors of nephrite are dulled somewhat by brown tones in comparison to the more highly saturated chromium derived hues of green jadeite.

[Typical "olivey"color of green nephrite, compared to the saturated green of fine jadeite (circa 1960's bracelet): Image courtesy of The Fraleigh Collection]

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As nephrite jade is, by definition, a mixture of amphiboles with an interlocking microcrystalline structure, pure actinolite or pure tremolite minerals, therefore are not jade. Actinolite sometimes occurs in a chatoyant form, though, which is often sold under the misnomer "cat'seye jade".

[Cat'seye actinolite] Nephrite is mined in many locales, ranging from New Zealand, Siberia and South Korea, to the USA (Wyoming and California primarily), but the largest deposits, by far, come from British Columbia. These Canadian sites often yield huge boulders, frequently covered with a brown rind of oxidized iron. The finest of this material is trademarked as "Polar Jade" and is of a translucent and rich green color seen in very few other specimens of nephrite. Large scale mining began there in 1995.

[Polar Jade earrings and a Polar Jade cabochon set into a pendant with Tsavorite and white zircon]

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[Jade boulders at the British Colombia site being cut into sizes that can be trucked out of the remote mine area: Image courtesy of Kirk Makepeace at www.jadewest.com] The wide distribution and useful properties of nephrite account for the world-wide useage of this stone by ancient cultures. Archeologists have retrieved tools and artworks made of nephrite in locations from Switzerland to New Zealand, the Americas, and Asia. This stone was valued highly by these people as it it could be used for tough knives, spears, hammers and axes, yet could be carved into exquisitely delicate bowls, figurines, masks and jewelry items. Its legendary toughness is a consequence of the interlocking "felted" nature of the tiny fibrous crystals within. Until the advent of steel, nephrite was the strongest available material for tools and weapons, less brittle and better able to keep a sharp edge than any other stone, or than copper, bronze or iron. Although nephrite artifacts date as far back as 3500 BCE in Europe, there is evidence documenting its use in China for more than 7000 years. The nephrite around which the Chinese built many aspects of their culture was obtained, technically, from Turkestan, a region not incorporated into China politically until after World War II. Known from legend as "The Stone of Heaven", nephrite attained a position in the religious and cultural life of these people that has not been seen with any other natural substance in any other time or culture. The two pieces shown below are contemporary Chinese nephrite carvings. The curled "dragon" is cut from "tomb jade" which has long been buried underground, and is stained and somewhat corroded with iron minerals, it is done in a faithful copy of a style from the Han Dynasty period, circa 200 BCE. The pure white citrus blossom carving is from Xinjiang Province (the traditional collection site of rare white nephrite) and shows the purity of color, translucence and desirable "greasy" luster of the best ancient materials.

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[Contempory Chinese nephrite carvings] For nearly all of the 7000+ year history of China's love of jade, it has been nephrite that was the object of affection and reverence. Only in 1784 was jadeite imported in quantity to China to begin its rapid "takeover" in popularity. The Maori of New Zealand have had as initimate a relationship with nephrite as the Chinese, if not nearly so long a one. Known as "pounamu" or greenstone it was used for weapons, tools and ornamental and religious objects. Some of the most advanced nephrite carving in the world has been done in recent years by New Zealanders using some of the superb local material. The piece below is a sublime example from the hand of Donn Salt.

["Uroboros": Image courtesy of www.donnsalt.com] The USA produces three notable types of nephrite: black with magnetite inclusions, and "Vonsen Blue" jade, both from California, and the green to black material from Wyoming.

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[Black nephrite with gold electroplated magnetite inclusions from California, black nephrite from Wyoming]

["Vonsen Blue" nephrite jade from California: cut cabochon set, rough slab] The name "nephrite" derives from the early belief that carrying talismans of certain green stones would cure or ward off ailments of the kidneys, although ironically, scholars have found that jadeite was actually the stone so used. One of the most widely available of gems, nonetheless nephrite has been extensively imitated. Natural simulants often presented (knowingly or not) as nephrite include bowenite, Vesuvianite, serpentine, aventurine, amazonite, verd antique and massive grossular garnet.

[Natural nephrite simulants: Vesuvianite cabs, green aventurine quartz beads] Nephrite is sometimes enhanced by dyeing, heating and waxing, although the prevalence of such treatments is not nearly as high as with jadeite gems. A man-made glass imitation called "metajade" or "imori stone" is sometimes found in the market, although true synthetic nephrite is not. Nephrite gems or art objects require no special care, they can be safely cleaned in ultrasonic baths and steamers. Traditionally nephrite gems are given in honor of the 12th wedding anniversary.

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VALUE CONSIDERATIONS In general, per carat values for nephrite gems are modest. The highest prices in jewelry pieces go to those with the greatest translucence and most pleasing colors or patterns or those that have been artistically carved. In some cases collectors pay higher prices for gems mined in specific locations, or those cut by certain artists. In art objects, the delicacy of the carving and antiquity of the piece are the prime determiners of value.

Gemological Properties: Makeup: Calcium magnesium iron silicate Hardness: 6 - 6.5 Toughness: Exceptional RI: 1.61 -1.63 Density: 2.96 Polish Luster: greasy to vitreous Fluorescence: none Fracture: rarely seen

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Botryoidal Gems When certain minerals occur in aggregates of tiny crystals rather than single large ones, one of the habits they can adopt is named "botryoidal". The word is derived from the Greek word for grapes, and means tiny crystals occurring in closely interlocking spherical masses or "bubbles" which can sometimes look like bunches of grapes. Those in which the masses tend to be less distinct and grade into one another are termed "sub-botryoidal".

[Sub-botyroidal hematite and carnelian] Several species and varieties commonly occur as botryoidal gems, in particular some types of chalcedony, Smithsonite, malachite, and azurite. At least one variety of chalcedony, fire agate, is defined by this property--> being a botryoidal growth of platy crystals of limonite over layers of chalcedony. Fire agate is the most valuable of the botryoidal gems and has been treated separately in another essay.

[Fire Agate] Botryoidal gems are fashioned into cabochons, carvings or ornamental objects and can be very interesting and lovely. There's a wide variation in appearance, based on whether the bubbles are large or small, uniform or different sizes, if the botryoidal surface is confined to recesses or not, and whether or not the surface is covered with drusy crystals. Furthermore, the lapidary can treat the material in various ways: sometimes the botryoidal surface is left in its natural state, sometimes it is polished and occasionally some or all the the bubbles are flattened to reveal the inner layering. 357

[Botryoidal malachite cabochon, botryoidal drusy quartz carvings]

[Botryoidal gems with different surfaces treatments: natural (Smithsonite), flattened (agate), polished (blue chalcedony)] Botryoidal gems make an interesting sub-collecting area within the gem hobby, and they can be used in beautiful and distinctive jewelry pieces as well.

[Botryoidal carnelian with grossular garnets and honey chalcedony]

Value Considerations Rarity and beauty would be the major value determiners in this group of gems. Malachite which commonly takes this form and is widely available is less valuable, say, than Smithsonite, which is a much rarer material, or than botryoidal prehnite which comprises only a tiny fraction of all prehnite. The beauty of the material itself, how intense or unique the display of bubbles and the artistry of fashioning are all important factors in determining value of a specific piece.

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Gemological Properties: (Vary by Species, those below are for quartzes) Chemical Composition: Silicon Dioxide (SiO2) Crystal System: Hexagonal RI: 1.54 - 1.55 Density: 2.65 DR: .009 Cleavage: none Luster: Vitreous Fracture: Conchoidal Hardness: 7 Toughness: Good

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Hardness Hardness is a gem's ability to resist scratching of its surface. This property derives from the crystal structure of the gem in virtue of how densely the atoms are packed, and how strong the binding forces between them are. It not only affects durability, but also has implications for the potential luster of the polished gem, and dictates what sort of tools, abrasives and polishes the lapidary requires to work with it. Most everyone has run across the Mohs' Scale of hardness which ranks materials in a kind of pecking order from 1 at the low end (can't scratch anything other than itself) to 10 at the high end (scratches all other gems, including itself). This scale was set up by the Austrian mineralogist, Friedrich Mohs, in 1827. He chose talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum and diamond as the representatives of hardnesses 1-10, respectively. Mineralogists and geologists can determine the approximate hardness of their specimens by using a set of "hardness points" which are metal pens set with pointed tips made of these minerals. The unknown specimen's hardness is determined by sequentially using the points until the one which will not scratch the specimen is found. So, if hardness point #8 will scratch the item, but #7 will not, then its hardness lies between 7 and 8. A kind of field, or practical, version of this test is often used by rockhounds and amateur geologists: 1, 2 (VERY EASILY AND EASILY SCRATCHED BY FINGERNAIL) 3,4 (VERY EASILY AND EASILY SCRATCHED BY COPPER COIN) 5,6 (VERY EASILY AND EASILY SCRATCHED POCKET KNIFE BLADE) 7 (SCRATCHES WINDOW GLASS, SCRATCHED BY STEEL FILE) 8 - 10 (SCRATCHES WINDOW GLASS, NOT SCRATCHED BY STEEL FILE) The numbers on this simple and useful scale are sometimes misunderstood to be linear or proportional in their meaning, which is not true. In order to get precise determinations of hardness a device called a sclerometer is used. It pushes a diamond point into a surface and measures the exact force 360

needed for penetration. This type of test belies our feeling that apatite (4 on the Mohs' Scale), must be about half as hard as topaz (8 on the Mohs' Scale). Sclerometer readings show that a topaz gem requires 8.5 times the force to scratch as does an apatite. For corundum (9) and diamond (10) the difference is even more striking--> with diamond testing as 140x harder than sapphire. Soft Gems

[Ivory & jet = 2.5, pearl = 3, sphalerite = 3.5, fluorite = 4] Intermediate Gems 361

[Scapolite = 6, Tanzanite = 6.5, garnet = 7. - 7.5, tourmaline = 7.5] Hard Gems

[Spinel = 8, topaz = 8, chrysoberyl = 8.5, corundum = 9] Hardness can vary with crystal direction. The most famous example of this phenomenon is the gem kyanite with dual hardnesses of 5 and 7, depending on direction. Going with the "weakest link" idea, we are well advised to treat kyanite as a relatively soft gem. Lapidaries working with this gem have to constantly adjust their pressure and speed so that progress is made on the harder areas, yet softer areas are not overcut.

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[Kyanite: H = 5 & 7] Interestingly, if diamond crystals did not vary in hardness with direction, they couldn't be cut and polished with diamond abrasives. The diamond cutting process uses a slurry of tiny crystals of natural or synthetic "bort" (industrial grade diamond) on a spinning cast iron surface (lap). As the various facets of the diamond are cut and polished, they are subjected to these randomly oriented crystals, at least some of which have harder surfaces exposed than the facet being cut. The hardest crystal direction of a diamond is the "octahedral" face which, literally, cannot be polished. Part of the job of the diamond cutter, then, is to orient the rough to avoid this plane in any of the facets. Even with the variable hardness factor, diamond cutting is time consuming. It requires specialized equipment, capable of greater rotational speed of the cutting wheel and greater pressure on the gem than does equipment used to cut colored stones. Although there are a few cutters who have the skill and equipment necessary to work both with diamonds and colored stones, the vast majority specialize in one or the other. Although hardness is an important characteristic in a gem, it is by no means the final measure of a gem's wearability or suitability for a particular use. All other factors being equal, the harder the gem, the better it will wear. But, there are two other factors which can make all the difference in the world: a gem's toughness and its stability. Each of these attributes will be treated in subsequent essays, but for now, a brief synopsis. Toughness is the ability to resist breaking or chipping, and is an extremely important consideration when selecting a gem for, say, an engagement ring. A hard gem will retain its polish, but if it is not tough, it may chip or break. A notable example is topaz. With hardness 8, it might seem ideal for an everyday ring or bracelet, but it is, in fact, a rather fragile gem due to its 363

tendency to cleave (break cleanly along a cyrstal plane). Topaz though unlikely to scratch, may chip or break with hard, constant wear. On the other hand, the jades with a hardness between 6 and 6.5 might seem poor candidates for heavy wear, but truth be told, they are the toughest of all natural gem materials and wear like iron! Their seemingly contradictory historical uses, both in the most intricate and delicate carvings, and as workaday tools such as axes, is testament to this durability. Stability meaures a gem's ability to resist changes due to light, chemicals and heat. It's little comfort to have a hard and/or tough gem, if it can be altered by absorbing chemicals from the air or from your skin, like pearls, or if its color changes due to light exposure like brown topaz. In general, jewelry that is worn more than occasionally should be set with gems of at least hardness 7 and that have good toughness and stability. Softer, more fragile, and less stable gems can be enjoyed in jewelry that has protective settings or which is worn gently. Extremely delicate gems are best kept as collectors' objects.

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Jadeite Jade Not recognized until 1863 as two separate minerals, jadeite and nephrite: aggregate minerals that overlap in color and transparency and have been used for tools and art objects throughout history, are both called "jade". In most instances, jadeite is the more valuable member of the pair, especially in its highest quality where the price per carat can rival fine emeralds and diamonds. The granular, interlocking pattern taken by the tiny crystals in the aggregate accounts for its exceptional toughness enabling it to have been used both for tools with strength greater than most metals, and at the same time for the most delicate of carved artworks.

[Highly translucent, white and light green Burmese jadeite forms the delicate flower petals and leaves of this 1920's vintage Chinese artwork.] We usually associate jadeite with China, but that connection (which is undoubtedly major) is fairly recent. Throughout the several thousand year history of Chinese use and veneration of jade, it was nephrite which was the focus. Jadeite has supplanted nephrite in the "hearts and minds" of the Chinese in only in the last 200 years or so, since the time it first began to be imported there from Burma. Burma is still the major world source, especially for the finest material, but Guatemala, Russia, Kazakstan, Turkey and the USA (California) also contribute.

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[Jadeite from around the World: yellow Burmese fish carving, purple Turkish cabochon, vivid green Kazakstani cabochon, California jadeite tablet] Jadeite can be semi-transparent to opaque and covers the spectrum from colorless through white, green, yellow, brown, red, orange, violet, to grey and black in color. In general, the color range and saturation values are greater than with nephrite, as is the maximum possible degree of translucency. Some of the colors are given variety, folk or trade names such as Imperial, apple green, moss-in-snow or chloromelanite. Imperial is the variety with the most highly saturated green color, apple green has some yellow, spinach green is darker and less vivid than Imperial or apple green, moss in snow has patterns in white and green, and chloromelanite is such a dark green as to appear black. Various combinations of chromium and iron are responsible for the different colors.

["Shades of Green": apple green ring, spinach green earrings, moss-in-snow cabochon] Well polished pieces have a "patent leather" shine, but considerable lapidary expertise is necessary to produce it. Jadeite sometimes frustrates lesser cutters with its tendency to undercut, which can create a dimpled or "orange peel" surface. Virtually all of the jadeite in the mass jewelry market has been enhanced through some combination of heating, bleaching, dyeing or resin impregnation. It's generally easy to spot such treatments as the stones look too uniform and saturated in color, whereas all but the very highest grades of natural color material show some mottling of lighter and darker colors, and more or less translucent zones. Reputable vendors designate three grades of jade: "A" jade, which has had no enhancing treatment of any 366

kind, "B" jade, which has been bleached or acid treated to remove dark spots and resin impregnated to fill the resulting voids, and "C" jade, which has been bleached, resin impregnated and dyed. It is relatively common for jadeite, even in top grades, to get a simple surface polish with a layer of colorless paraffin or beeswax. Jadeite of inferior color is usually dyed, while that of decent color but with unattractive inclusions is subjected just to the bleaching/resin process. All the specimens of jadeite pictured in this essay are A jade. If you look around most of the mass market venues: trade shows, catalogs, home shopping channels, online auctions, etc., you will see B and C jade in abundance--> but, in fact, you will rarely, if ever, see A jade. The ubiquitous presence of these brightly dyed and othewise enhanced jades has in some eyes diminished the beauty of the more subtle colors of natural jades, and leads some to question the much higher costs associated with the "real deal".

[Two perennial "A" jadeite favorites in my personal jewelry collection] Fine chrysoprase is sometimes used as a jadeite simulant, and in its best grades has been successfully passed off as apple green, and even Imperial green jadeite. Aventurine and serpentine are also common natural simulants. An early, and still used man-made imitation of jade, is glass, which can usually be revealed by the presence of microscopic bubbles (which would never be seen in real jade). Jadeite has just recently been synthesized (by General Electric Laboratories, a leader in making synthetic gems for research), but lab created stones have not yet made an entry into the gem marketplace.

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[Jadeite?: chrysoprase cabochon, aventurine quartz Buddah, 10x view of glass jade imitation, showing bubbles: Image courtesy of Martin Fuller] Due to its superior toughness, natural jadeite can be used for any jewelry application and needs no special care in cleaning or wearing. It can be scratched, though, by harder gems like sapphire or diamond and so, as with any fine jewelry, pieces should be given their own separate "berth" in the jewelry box. Dyed or resin impregnated pieces may fade or discolor with time.

Value Considerations By far, the most valuable variety of jadeite is that termed "Imperial". The finest of these gems are nearly transparent and have the most highly saturated, even, green color, rivaling (some would say surpassing) the finest emeralds. Such pieces are extremely scarce and astronomically expensive--> the name derives from the time when only the Imperial household was permitted, and could afford to own it. Among the other green colors, the next most valuable shade is termed "apple green". Fine, translucent, lavender pieces can rival good greens in price, whereas highly mottled or opaque gems are worth considerably less. Cholormelanite has some value as a scarce collector material. As with nephrite, much of the value in jadeite works of art comes from the skill with which they were carved or the antiquity of the pieces. Enhanced material is very modestly priced.

Gemological Properties: Makeup: Pyroxene: NaAlSi2O6 Hardness: 6.5 - 7 Toughness: exceptional RI: 1.66 - 1.68 Density: 3.25 - 3.36 Polish Luster: greasy to vitreous Birefringence: .012 - .020 368

Specific Gravity Specific Gravity (SG), or the relative density of a gem material, is important to gemologists in identifying an unknown specimen, and to jewelers and jewelry lovers in matching the setting size to the gem weight. SG is calculated as the ratio of the density of a given volume of the gem to the same volume of water. Amethyst has a SG = 2.65 which means that a cubic inch of amethyst weighs 2.65 times as much as a cubic inch of water. The range in SGs for gemstones extends from slightly above 1 to nearly 7. What Determines SG? One might ask, why so much variation? Basically the density of any material will be determined by the weight of the parts of which it is made (in this case various chemical elements) and how those parts are put together (are they closely or loosely packed in their crystal lattice?). In general, gems which have heavy elements in their chemical formulas, like lead or iron, and those whose crystal structures pack the atoms tightly, have high SGs while those made of lighter elements or those with loosely packed crystals have low SGs. An example of the atomic weight factor would be the difference between corundum (sapphire or ruby) Al2O3 and hematite Fe2O3. Aluminum = atomic weight 27, Iron = atomic weight 56. (Imagine the weight of a one inch cube of aluminum in your hand versus a one inch cube of iron)

[sapphire SG = 4.0 (aluminun oxide), hematite SG = 5.2 (iron oxide)] An example of the crystal packing factor would be the case of diamond and graphite. Both have the same chemical formula, C, but in diamond those carbon atoms are much more tightly packed than in graphite, so diamond's SG = 3.5, whereas that of graphite is only 2.2.

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[Diamond, graphite] For purposes of this essay I will somewhat artificially group gems in terms of their density as light (SG less than 3), medium (SG between 3 and 4), and heavy (SG greater than 4). Light Gemstones

[amber SG = 1.08, opal SG = 2.10, agate SG = 2.65] Medium Weight Gemstones

[peridot SG = 3.0, jadeite SG= 3.3, chrysoberyl SG= 3.7] Heavy Gemstones

[zircon SG = 4.7 scheelite SG = 6.1, cassiterite SG = 6.95] Measuring SG Specific gravity can be measured rather crudely just by "hefting" a gem. Plastic and most glass imitations are notably lighter than the natural gems they simulate, and many diamond simulants are quite a bit heavier than diamonds. For example, CZ has a much higher SG than diamond (5.8 as opposed to 3.5). 370

Savvy jewelers can often discriminate cubic zirconia from diamond by the simple hefting technique, as they are quite familiar with the weight of various sized diamonds. If a stone is too heavy for a diamond of its size, suspicion is aroused. Along the same line, but more precise, would be the use tables of sizes and weights such as found in appraiser's and jeweler's manuals. Measuring the size of a gem and checking the expected weight for the species it is supposed to be, can often weed out simulants, although it is of no use with synthetics whose SGs are the same as their natural counterparts! Such a table would tell you that a 6.5 mm round diamond should weigh 1.0 ct (if cut according to standard proportions) whereas a 6.5 mm round CZ is expected to weigh about 1.65 ct. For this reason, when the home shopping networks sell their CZ diamond simulants, they do so in "diamond equivalents". So a "1 ct" CZ from those sources is the size of a 1 ct diamond not the weight of one! Here is a quote from the FAQ page of the HSN.com website: What is Absolute™? Absolute is HSN's exclusive brand of high-quality simulated diamonds. Absolute is often combined with precious metals and genuine gemstones to create dramatic designs. Absolute stones are listed with diamond equivalency weights - to help you compare Absolute to genuine diamonds and gemstones. SG in Gem ID There are two commonly used ways to determine the specific gravity of an unknown: heavy liquids and hydrostatic weighing. Heavy liquids use the bouyancy principle that says a solid will sink in a liquid whose SG is lower, float in one whose SG is higher, and remain suspended in a liquid whose SG is equal to its own. Sets of heavy liquids with known SGs are used to determine (within a range) the SG of unknown gems. Besides being imprecise, this method uses smelly and potentially hazardous chemicals and can damage porous gems.

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[Heavy liquids set for determining approximate SG] Hydrostatic weighing compares the weight of the gem in water to the weight of the gem in air with a specially rigged balance. Using these two values and a formula based on Archimedes' Principle one can calculate the SG very accurately. Although more expensive and time consuming to use than heavy liquids, there are no hazards associated with the technique and gems are not damaged as a result.

[Electronic balance with hydrostatic weighing apparatus] Unfortunately neither of these methods is useful with mounted stones. I'm not a gemologist, jeweler, or appraiser -- why should I know about SG? An example of how a non-gemologist might benefit from this information was brought to my attention recently when an acquaintance said he wanted 372

to get a 1 ct. round amethyst to take the place, in an old setting, of a 1 ct. round diamond that had been lost. Since quartz has a significantly lower SG than diamond, a 1 ct. amethyst would be about 7.1 mm in diameter, too large for the 6.5 mm setting that held the diamond--> but a .80 ct. amethyst would fit perfectly!

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PYRITE If I asked you whether you had, or knew any one who had, any pyrite jewelry, you'd probably say no. But most of us have at least one piece set with "Marcasites", usually with an oxidized silver setting and perhaps with black onyx accents. Although many years ago there was some use of true Marcasite as a gem, it has long since been replaced by its close relative, pyrite, which looks nearly identical, but is much more plentiful, stable and wearable. Along the way nobody ever bothered to change the name, so we keep on using the Marcasite misnomer. The glittery points of flashing light which make this type of jewelry sparkle come from bead set "rose cut" pyrites (flat bottom, with the crown faceted to a point). No matter what we call it, this brassy yellow, iron sulfide mineral with its glowing metallic luster is a lovely gemstone. Its worth and prestige have been unduly "tarnished", to my mind, by the unkind epithet of "fool's gold" with which it has often been burdened. The name pyrite ("mineral of fire") is a reference to the fact that it will emit sparks when struck by a metal hammer. Of the two metallic minerals commonly used as gemstones (hematite and pyrite) pyrite is by far, the more common and versatile. Pyrite is, in fact, the most common sulfide mineral on Earth--> it can be found in sedimentary, metamorphic and volcanic rocks and although the crystal habit is affected, it will crystallize at a variety of temperatures and pressures. Each temperature/pressure/host rock combination seems to produce a different crystal habit so that pyrite is one of the most variable minerals in that regard. Within the hobby of mineral specimen collecting, there is a healthy sized group who specialize just in the various forms of pyrite. Probably the most common of these you might have seen in rock shops are the cubes, octahedrons and "suns" (flattened disks), some of which also show themselves as lovely inclusions in transparent jewelry stones. Another place pyrite surfaces, so to speak, is as the "gold" streaks which give certain cabochon gems, such as "Apache Gold" and "Oro Verde Serpentine" an appealing glimmer.

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[Graduated set of natural cubic pyrite crystals: Image courtesy of Treasure Mountain Mining] Besides masquerading as Marascite and starring as gem inclusions, pyrite also "pyritizes" fossils. Most commonly we see fossil ammonites whose shell minerals have been replaced with the metallic yellow pyrite or its oxidized iridescent form. These dual productions of the forces of biology and geology, although quite inexpensive, are among the loveliest objects of Nature.

[Pyrite crystals in shist , pyrite "sun" in quartz]

["Oro verde" serpentine, pyrite "suns", rose cut pyrite cabochon]

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[Pyrite as "marcasite" in jewelry, 10x closeup of round and square cut pyrites in brooch , pyritized ammonite fossil] VALUE FACTORS: Pyrite reaches its greatest value in its various crystal forms as mineral specimens. Its value when used as a gem has generally been rather modest. Well pyritized fossils are admired, and may be even more valued when naturally oxidized to an iridescent finish. As an inclusion, it is the crystal habit which is on display, so look for specimens with distinctive and clearly visible pyrites. In jewelry, the brassy yellow color and strong metallic luster recommend this gem, so well polished specimens, with no matrix or inclusions, are the most sought after. GEMOLOGICAL DATA: Makeup: FeS2 Iron sulfide Crystal System: isometric (cubic) RI: > 1.81 (over the limits of the standard refractometer) Hardness: 6 - 6.5 Density: 5.0 Luster: Metallic

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Andalusite Andalusite is a strongly pleochroic gem which is largely unknown by the general public. It ranges in color from pale yellowish brown to dark green to dark brown. It's trichroic nature, which shows shades of brown, green and reddish brown depending on the path of light through the crystal, can be enhanced by specific orientation and cut. This stone has sometimes been marketed as "poor man's Alexandrite", but it is not a color change stone. The distinction being that pleochroism is seeing different colors at different viewing angles regardless of light source, whereas the color change phenomenon is seeing a change in hue due to change in light source, regardless of crystal direction.

[Faceted Andalusite: this specimen clearly shows blocks of the pleochroic colors] Those cuts with a long axis such as ovals, marquis or emerald cuts tend to separate the hues so that such a gem typically shows one color near the center and a second, usually darker color near the ends. Square and round cuts usually blend the colors into a mosaic. Most specimens contain some inclusions, the commonest of which is rutile needles. Brazil is the chief producer but Sri Lanka, Russia and the US are also sources, as is the site of original production, Spain (Andalusia). It is hard enough and tough enough for most jewelry uses. Poorly cut and polished stones are pretty dull and insipid looking, but a large, clean, well cut Andalusite is a show stopper.

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[Andalusite oval in pendant and long marquis have cuts which tend to create color separation, green in the middle and orangey brown on the ends]

Value Andalusite is a real gem bargain, due to its lack of recognition in the marketplace. Fine specimens can be had for less than stones of equivalent quality in many other groups. Color itself is less important in this species than the attractiveness of the pleochroic effect. Fine cutting adds value by increasing brilliance and enhancing either the color separation or mixing (both styles have their fans). As is true with ametrine, today's gem lover generally favors the blended mosaic appearance. Large stones are especially rare, any clean well cut specimen over 3 carats is a real find and will be relatively expensive.

Gemological Data Makeup: an Aluminum silicate Luster: vitreous Hardness: 7.5 Crystal structure: orthorhombic Fracture: distinct, one direction Cleavage: uneven to conchoidal Density: 3.16 RI: 1.63-64 Dispersion: .016 Birefringence: 0.01 Pleiochroism: Strong: brown, green, reddish brown

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Peridot To my mind, peridot is an under-appreciated gemstone. Perhaps this has become the case due to the public's familiarity with low quality, olivey material which is inadequately cut and polished. Admittedly it can look pretty awful, but the lime and apple green stones given custom cuts and polishes are something else again.

Peridot belongs to the forsterite-fayalite mineral series which is part of the olivine group. It is one of the "idiochromatic" gems, meaning that its color comes from the basic chemical composition of the mineral itself, not from minor impurities, and therefore it will only be found in shades of green. Historically important sources in Egypt have been superceded by today's main sources in Arizona and Pakistan and, most recently, China. The high birefingence of this gemstone necessitates careful orientation in cutting to prevent "fuzziness" of facet reflections through the table. Distinctive, disk-like liquid and gas "lily pad" inclusions can often be seen under magnificatiion. Peridot is one of the gems which can be assumed to be unenhanced and which is hard and tough enough for most jewelry uses, although use in rings 379

without protective mountings should be limited to occasional wear pieces. Peridot is the birthstone for the month of August.

Value The vast majority of peridot rough produces sub-carat sized stones which are ubiquitous in commercial quality jewelry and are quite inexpensive. Stones in the 1-4 carat range that have custom cuts and lack olive tones are much more highly valued and stones over 4 carats with good clarity, cut and color bring the highest prices of all. Gemological Data Makeup: an iron, magnesium, silicate Luster: Sub-Vitreous to Vitreous Hardness: 6.5 - 7 Crystal structure: Orthorhombic Fracture: conchoidal Density: 3.34 RI: 1.65 - 1.69 Birefringence: .036

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RUBY Ruby is corundum whose red coloring derives from chromium impurities, all other color varieties of this mineral species being referred to as sapphire. The ruby color range includes pinkish, purplish, orangey and brownish red gems depending on the chromium and iron content. The trace mineral content tends to vary with the geologic formation which produced the ruby, so that original place adjectives, such as Burmese and Thai, have come, in later years, to be sometimes used in describing color. To qualify as ruby, authorities expect a medium to medium dark color tone in a corundum gem, naming stones lighter than this, pink sapphire--> but there is no general agreement as to exactly where the line is to be drawn. The stone below is an example of a corundum gem that some would call a ruby and for which some, more conservatively. would use the term pink sapphire. The old saying about questionable stones goes: "Whether it's a ruby or a pink sapphire depends on whether you're the buyer or the seller"!

[Ruby or pink sapphire?-->a judgement call on some stones] Enhancement All corundum gems, including ruby, have a long history of enhancement. Unless the seller specifically states the stone is unheated you should assume that some kind of heat treatment has been used. Generally, high temperature heating and controlled cooling is done to clarify the stones, especially by dissolving "silk" (rutile); but it can also improve tone and saturation of color. Such treatments can only be detected in stones whose residual inclusions, or surfaces, show signs of heat stress; so completely flawless stones will give no clues, and cannot be positively verified as unheated. The general view at present seems to be that simple heating, being indistinguishable from Nature's own heating processes, and stable, is acceptable: as long as it is disclosed. For this reason such enhancement does not radically lower the value of ruby gems. Not so for gems treated with traditional dyeing (red ruby oil) or other, more recently invented, 381

treatments such as surface or lattice diffusion, or glass infilling. With the possible exception of some of the latest diffusion processes routine gemological tests can detect the treatments. Synthetics and Simulants Corundum was first synthesized in the early 1900's by a simple flame fusion process. Many jewelers and gemologists have had the unpleasant task of telling a proud heir that Grandmother's treasured ruby ring or brooch contains a synthetic flame fusion stone and has a lot more sentimental than commercial value. These stones are both the easiest to identify and the least expensive to produce. Such stones often show diagnostic growth features called "curved striae", neverseen in natural gemstones. More complex processes have been developed in recent years such as flux melting and hydrothermal synthesis. These so closely simulate natural formation conditions that colors, and even inclusions, look extremely natural, and such stones are difficult for all but the most highly skilled professionals to identify as man-made. Luckily there are several diagnostic inclusions such as "fingerprints" which identify a gem as natural ruby, and others which in many cases, can provide evidence for or against heating. Ruby simulants are many and varied including natural gems such as red spinel, rubellite tourmaline and garnet, and man made or enhanced materials like glass and dyed quartz. Historically, various assembled stones such as garnet and glass doublets have been used as well.

[Synthetic flame fusion ruby rough (boule), cut synthetic flame fusion ruby]

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[Curved striae in flame fusion synthetic corundum,"fingerprint" inclusions in natural ruby] Characteristics Ruby is hard (9) and tough, making it a superb jewelry stone. (Of course, a heavily included or fractured stone will be less stable.) For reasonably clean stones, no special wear or care precautions are necessary. Ruby shows pleochroism, which means that the color varies with the direction of viewing. Gemologists use a simple tool called a dichroscope to test for this property, which will easily discriminate ruby from its natural simulants like red spinel, garnet and also from glass. Most rubies show distinct purplish red and orangey red colors pleochroic colors, and the dichroscope displays them side by side for easy comparison.

[Simulated view of pleochroism of ruby as seen through a dichroscope] The overall color can often, but not always, give a clue to a stone's geographic origin, with Burmese stones tending to purplish red colors and Thai stones appearing more brownish red. In addition many rubies will fluoresce in long or short wave UV and this property can often be used to help identify a stone's geographic origin. Burmese rubies often fluoresce so strongly that the effect is noticeable even in sunlight. Such stones seem literally to glow, and are greatly admired. Thai and African stones generally lack this property due to their higher iron content. Although Asia has historically been the major producer of ruby gems, there are many other sources including the USA, Australia and most recently Madagascar.

/Burmese ruby ring under normal lighting, fluorescence under UV light] Uses

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Ruby rough of lower quality is used in great quantities to make cabochons, beads, carvings and other ornamental objects. The silk which is so common in corundum can, if sufficiently abundant and precisely arranged, lead to asterism which with proper cutting, creates star rubies. Today there are heating and diffusion processes which can increase the rutile content and improve such gems. Totally synthetic star corudums were very popular in the 1950's under the trade name "Linde Stars" and are still under production. At the pinnacle of beauty and value in the ruby world are the transparent faceted stones.

[Carved ruby beads, cabochon earrings, carved natural surface stone]

[Ruby in zoisite carving, gem quality natural star ruby]

[Faceted Burmese rubies] Few other gems have as much myth, lore and romance surrounding them, with one of the chief attractions being the protection from misfortune and bad health rubies were believed to afford their lucky owners. As the science of gemology developed, it became known that many historically important 384

"rubies" such as the famed Black Prince's Ruby of the British Crown Jewels, were actually other red gems, most often red spinels. Ruby is the traditional birthstone for the month of July.

Value: Rubies are the most valuable members of the corundum family. Large, gem quality rubies can be more valuable than comparably sized diamonds and are certainly rarer. Small gem quality rubies are rarer than comparable blue or other color sapphires, making even the littlest fine rubies relatively high in value. Many gems increase exponentially in value with increase in carat size, and this is particularly true of fine ruby gems. Of course there is a tremendous amount of lower quality ruby available in the market for reasonable to lower prices. Stones of Burmese origin generally command the highest prices. Strong color saturation, eyeclean or better clarity, and strong fluorescence elevate prices sharply. The vast majority of rubies are "native cut" in the country of origin. Many native cut stones have windows and poor proportions which mar the stones' brilliance and overall appearance. (Such cuts are not generally a sign of lack of skill by the lapidaries, though, but of the need to retain weight in the cut gem which is usually their highest priority). High value ruby rough is tightly controlled and rarely makes its way to custom cutters outside the country of origin. Occasionally, such native cut stones are recut to custom proportions, albeit at a loss of weight and diameter. Custom cut and recut stones are usually more per carat than native cuts, and my own bias is that they are "darn well worth it".

Gemological Data: Makeup: Aluminum oxide Crystal Structure: Trigonal Hardness: 9 Luster: Vitreous Density: 4.00 RI: 1.76 - 1.77 DR: 0.008 Disperion: 0.018 Cleavage: none 385

UV Fluorescence: dependent on origin and/or iron content, strong to inert, red or orangey red, with LW or SW

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Rhodocrosite This gem is known to the public primarily from the opaque to translucent aggregate form, generally seen in pleasant looking pink and white patterned cabochons. Good quality stones have high contrast between pink and white sections making the so-called "bacon strip" pattern. Pieces cut from stalactite formations often have concentric rings or "eyes". One of the "idiochromatic" gems (those which get their color from the constituent atoms of their basic formula rather than from trace impurities), it is colored by manganese. Named from the Greek word, rhodokhros, "of rosy color", rhodocrosite occurs in hydrothermal veins associated with manganese, copper, silver and lead, and sometimes as stalactites in caves. Major sources are Argentina, Mexico, South Africa and the USA.

[Typical "bacon strip" and bull'seye patterns of rhodocrosite] Only gem aficionados realize that this gemstone occasionally occurs in a highly translucent "gel" form, the finest of which have a rich, even, pink color and high translucence. Even more rarely, single crystals form which can be faceted. These pieces, especially the ones from Colorado's "Sweet Home Mine", are hotly sought after and greatly prized by collectors. Their wonderful hot pink, rose and watermelon colors, their excellent brilliance, and their, sometimes, pearly luster make them one of the most beautiful of all the collector gems.

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They are so beautiful that some succumb to the temptation to put such pieces in jewelry. This can be done, especially with the tougher aggregate form, but as the gem is sensitive to heat, acid and shock, extreme care in setting and extreme gentleness in wearing are necessary.

["Gel" cabochon, stalactite slice and crystalline rhombs set into jewelry] The pink color, lovely patterns and ready availability make this gem a favorite of intarsia artists and carvers.

[Multi-gem intarsia featuring rhodocrosite, a pair of carved "wings"] 388

The number of specimens of facet quality are very few to begin with, and, those same crystals are coveted by mineral collectors, further diminishing the supply. This high grade crystalline material is not only extremely rare, but very difficult to facet, due to its softness (3.5 - 4.5) and the perfect cleavages.

[Range of colors of gem rhodocrosite] There are no enhancements or synthetics to worry about. The look of cabochon grade material is so distinctive that this is one of the few cases where a "sight identification" might be justified. The gem rhodonite is also rosy pink, but is easily distinguished, in most specimens, by the presence of dark, usually black, rather than light markings. The distinction between these two species is less straight forward with gel and facet grade specimens, though. Faceted rhodonites are usually darker red and are even rarer and more difficult to cut than rhodocrosite, so they are usually more expensive as well.

[Rhodonite cab and faceted stone] Value By far, the most valuable specimens are the rosy to watermelon pink faceted stones with saturated color, and eyeclean or better clarity. Fancy cuts add value--> the material is so difficult to cut that most facetors who attempt it stick to the basics using as few facets per stone as possible. There is, as in many gems, an exponential increase in value with size, since crystal sections clean enough to facet are quite rare.

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In cabochons, the gel pieces or those with some translucent areas, are valued more highly than fully opaque stones. Those with particularly attractive markings, such as stalactite "bull'seyes" are preferred as well.

Gemological Data: Makeup: Manganese Carbonate (MnCO3) Luster: Vitreous to Pearly Hardness: 3.5 - 4.5 Crystal structure: Trigonal Fracture: uneven to granular Cleavage: perfect, in three directions Density: 3.60 RI: 1.60-1.80 Birefringence: .220

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Dispersion Dispersion, refers to an optical property of gemstones whereby flashes and pinpoints of spectral colors are displayed as the stone is turned in the light. The dispersive colors we see are not really there in the gem, instead, they are created by the behavior of white light in the stone. Dispersion results when light passes through a transparent material with inclined surfaces (like a prism, or a faceted gemstone). Although the term "fire" is gemologically equivalent to dispersion, "fire" is so frequently misused to mean either brilliance (total light return) or scintillation (twinkling), that I prefer to use "dispersion" in all my descriptions for the sake of clarity.

[Visible light range of the electromagnetic spectrum] White light is, of course, made up of a spectrum of wavelengths from relatively long (red) to relatively short (blue and violet). Each of these wavelengths is bent to a different degree (red less, blue more) when passing from air into a denser medium like a gemstone. When the bent light waves exit through an inclined surface (like a facet), depending on the degree of bend (or refraction), they may show as distinct spectral colors. The ability of a gem species to show dispersion is, therefore, roughly correlated with the density and refractive index of the gem material itself. This property is a distinctive characteristic of each gem species and can be used in the process of identifying a gem. Testing for dispersion in gems, however, is actually a rather painstaking and complicated process involving measuring the separate refractive indices of the red and blue wavelengths in that species and calculating their ratio. Instead, most gemologists and gem lovers simply gauge dispersion by eye. There are published tables (see below) of the laboratory values for each species, but in actuality several other factors may enhance or depress the display in a given stone. Foremost among these is body color. For example, two species with high values for dispersion: demantoid garnet and Benitoite 391

tend to have fairly dark body color which usually masks the effect to a great degree. Fans of dispersion and fans of rich color often part company over which is more beautiful--> a saturated medium dark blue Benitoite which shows little of its potential dispersion, or a substantially lighter one with spectral colors flashing at every turn. (As a card carrying Benitoite fancier, I am definitely in the latter category!) The 2.0 ct. Benitoite stone in this pendant has, to my eye, an optimal balance between color and dispersion.

[Beniotite showing dispersion] The two sphalerites below show the effect of darker body color on dispersion, the yellow stone showing much more than the darker orange stone.

[Yellow sphalerite, orange sphalerite] In general, the larger, cleaner and lighter in color the gem, the more of its potential dispersion will be visible. Cutting style has a noticeable effect as well, in that higher crowns accentuate the effect and flatter crowns diminish it. (I once cut a large, light lavender spinel (a species with modest dispersion figures) with an extremely tall crown that had more "fire" than a lot of poorly cut diamonds I have seen. Diamonds have always been admired for this property, and so diamond simulants have been sought that have similar dispersive characteristics. Up

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until a few decades ago, the diamond simulant of choice was white zircon, whose dispersion and high luster make it a good visual replica for diamond.

[Diamond, white zircon] Synthetic rutile and strontium titanite were each briefly popular when first synthesized, but were noticeably more dispersive than diamond and so, not very convincing.

[Synthetic rutile, strontium titanite] YAG (yttrium aluminum garnet), was also used, but with dispersion noticeably less than diamond, it was unsatisfactory as well.

[YAG] Cubic zirconia now has the lion's share of the simulant market, among other reasons, because its dispersion, though higher than diamond is close enough to look right, especially in sizes most commonly used in jewelry. 393

[Cubic zirconia, CZ] In the list below are a few species that might be seen in today's marketplace that typify gems with low, moderate, high and very high dispersion values: Low • • • • • • •

Fluorite: .007 Silica Glass: .010 Quartz: .013 Apatite: .013 Beryl: .014 Chrysoberyl: .015 Crown Glass .016

Moderate • • • • • • • • •

Iolite: .017 Danburite: .017 Tourmaline: .017 Kunzite: .017 Corundum: .018 Spinel: .020 Peridot: .020 Spessartite Garnet: .027 YAG: .028

High • • • • •

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Zircon: .038 Lead or Flint Glass: .041 Diamond: .044 Benitoite: .044 Sphene: .051

• •

Demantoid Garnet: .057 Cubic Zirconia: .066

Very High • • •

Sphalerite: .156 Strontium Titanite: .190 Natural and Synthetic Rutile: .280

**********

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Tanzanite Truly a modern gemstone, transparent zoisite of a naturally yellowish brown color which can be heated to a stable blue to violet, was discovered in the shadow of Mt. Kilamanjaro in 1969. Although other varieties of opaque zoisite were well known, they made no impact on the gem market. Tanzanite's rise to prominence among retail jewelers and the general public has been rapid and dramatic. Naturally trichroic, the species shows different colors when viewed through each of its three crystal axes: blue, red-violet and yellow-green. Although the occasional blue-violet stone is found in the rough state (Mother Nature in this case has already provided the heating); the vast majority of them must be heated to create this color. Usually stones are cut and polished prior to heating to about 700 degrees Fahrenheit, as abrasions, fractures and inclusions in the rough can cause cracking. This means that the cutter has to attempt to orient the stone for best color prior to the color change. It is the yellow-green color which is altered to colorless by this treatment leaving just the other two more attractive color axes. Another important decision which must be made by the cutter is the choice to go for size (usually the more violet orientation yields the largest stone) or blueness (blue orientation yields smaller gems). A very small fraction of Tanzanite rough heat treats to a green or blue green color and such stones are valued by collectors. (Technically they should be called heated green zoisite, but everyone calls them "green Tanzanite" anyway.) In the trade, all Tanzanites are assumed to be heat treated and the color is stable. Initially, blue stones were valued as a substitute for sapphire, but gradually an appreciation for the more violetish tones has built up. Tanzanite is used frequently as a ring stone, but with its hardness of 6.5 daily wear will dull the finish and its brittleness is a hazard. It is better suited to earrings, pendants, tie pins and occasional wear rings or those with protective settings. Recent disastrous weather conditions, mining accidents, government embargos and continuing political tensions have restricted the supply, especially of larger finely colored stones. Tanzanite simulants range from less convincing glass and synthetic corundum stones whose lack of dichroism is a give away, to more convincing synthetic Fosterite pieces which must be detected by refractive index or specific gravity measurements. Recently, coated natural origin stones with micro-thin layers of rich color over pale cores have entered the market, 396

especially in the smaller sizes 3 - 4 mm) found in cluster-type jewelry settings or as side stones.

Value In general, stones showing more blue are valued higher than those showing more violet and medium dark colors are the ideal. Custom cuts add value. As always, size and clarity have a strong effect on prices--> large clean rough is extremely scare, and now in addition has been limited for export, so larger, fine gems are rapidly rising in price and decreasing in availability. Collector types such as greens or the ultra-rare cat'seye stones are highly sought after and quite valuable.

[Tanzanites showing: more violet, more blue]

[Unheated "Tanzanite", rare cat'seye and "green Tanzanite"] Gemological Data Makeup: Calcium, aluminum, hydroxysilicate: Ca2Al3(SiO4)3OH Luster: Vitreous Hardness: 6.5 Crystal structure: Orthorhombic Fracture: concoidal to uneven Cleavage: 1, perfect 397

Density: 3.35 RI: 1.69 Pleiochroism: Trichroic, blue, red-violet, yellow-green Birefringence: .010

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Fluorite Fluorite (calcium fluoride), historically called Fluorspar, has been used in carvings and decorative objects for hundreds of years, but the availability of faceted pieces is a relatively new development. Not readily useable in jewelry due to its softness, and perfect cleavage in four directions, it is primarily a collector's gem. Faceting this material presents considerable challenges, but well cut and polished gems can be very bright and appealing. The first picture below shows a close-up of a typical piece of fluorite rough showing natural cleavages, note the steep 90 degree breaks. Although fluorite sometimes forms octahedral crystals naturally, most of the fluorite octahedrons sold to collectors are actually those which have been deliberately cleaved into that shape. (If the cleaver knows exactly where to hit the crystal, these form readily and need no polishing!).

[A piece of fluorite rough showing natural cleavage surfaces, a cleaved fluorite octahedron] The name from the Latin "fluere" refers to the fact that it melts easily, a property which makes it useful industrially as a flux in steel production. Other industrial uses of non-gem grade fluorite vary from the production of hydrofluoric acid to the manufacture of "opalescent" glass, to coatings for special lenses for cameras and telescopes. The latter use is occasioned by the extremely low dispersion of this mineral. (Dispersion is the splitting of white light into spectral colors -- a feat desirable in a gemstone, but inconvenient in precision optics!) Some might think that the name fluorite derives from the fluorescence shown by some specimens of the mineral, actually, just the opposite is true. The property of fluorescence was named for this mineral which many scientists used in the early studies of the phenomenon.

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[A pale pink fluorite specimen fluorescing strongly to UV radiation] Fluorite mines are widespread, with the most important current supplies originating in Switzerland, USA, Australia, Germany, Mexico and Nambia. The largest US deposits occur in Illinois where fluorite is the official "State Mineral". The deposits are generally formed when near surface hydrothermal waters, invade calcium rich rocks like limestone, via cracks and openings, or in the vicinity of hot springs. The crystals can take many forms most commonly massive, cubic and, on occasion, octahedral, and the well-formed ones are eagerly sought by mineral collectors. The color range of this mineral is as wide as its distribution, ranging from purple, green, blue, yellow, orange, pink and brown to multicolor with bands or swirls of contrasting colors.

[Banded and vivid green faceted stones, more delicately colored fluorite carvings] One of the most famous of all gem fluorite mines, located in Castleton, Derbyshire in the UK, and now, sadly, virtually exhausted, produced the famous "blue john". This banded, translucent, cream and blue-purple fluorite was extensively used throughout Europe over at least fifteen centuries to produce stunning vases, sculptures, and ornamental items. The very small production remaining today goes almost exclusively to custom jewelry. Quite recently a deposit of colorful and durable, highly silicated, massive fluorite was discovered in Utah, and has been given a number of fanciful names: Picasso Stone & Bertandite, to name two. More properly called "opalized fluorite" it makes attractive cabochon gems.

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["Blue-John" fluorite ring from the Castleton deposit, opalized fluorite cabochon from Utah]

Care and Cleaning Care considerations include protecting stones from hard knocks, rapid temperature changes, and strong chemicals. Cleaning in warm water and mild soap is safe. Known enhancements are limited to plastic or resin impregnation to improve stability, and are rare in the marketplace. Due to the ready availability and low cost of natural material no synthetics are marketed.

Value Factors As large crystals are common, size in a finished piece is a minor value consideration. Most banded fluorites or those in common colors are quite inexpensive and readily available as native cuts. Premium prices are obtained only for those pieces with fine faceting and polish, or those with unusual colors.

Gemological Properties Makeup: Calcium fluoride Hardness: 4 Refractive Index: 1.43 Dispersion: .007 Density: 3.18 Crystal System: Cubic Luster: Vitreous UV Fluorescence/Phosphorescence: Strong, variable Toughness: Fragile due to brittleness Cleavage: Easy in 4 directions

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Chrysoprase Chrysoprase is chalcedony (microcrystalline quartz) whose rich green color is derived from the presence of minute particles of a nickel containing mineral, willemseite. The derivation of its beautiful color is, then, analogous to chrysocolla chalcedony's coloration by particles of the copper mineral chrysocolla. Chrysoprase, with nickel as a chromophore, is notable among green stones as the majority are colored by iron (like peridot), or chromium (like emerald and chrome tourmaline), or vanadium (like Tsavorite garnet). Geologically it forms as a precipitate from solutions containing silica and nickel compounds, generally derived from the weathering of serpentines. These solutions crystallize in fissures, cracks and cavities in various types of rocks. Historically deposits have been found in Eastern Europe, the US, Russia and Brazil, but by far the lion's share of today's World chrysoprase production comes from Australia. The name, derived from Greek for "golden + leek" belies the green color, but may have reflected either yellowish local deposits, or as so often happens in gemological antiquity, the transfer of names from one gem material to another as time passed. Colors range from near emerald, to apple, to leek green, with or without matrix, and diaphaniety ranges from nearly transparent to opaque.

[Chrysoprase extremes: from nearly transparent in these carved leaves to opaque with black matrix in the cabochons]

At one time the duller, leek green stones were called prase, and the more vivid apple greens ones chrysoprase, but this distinction is given little attention today.

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[Roughs of apple and leek green material which may sometimes be distinguished as chrysoprase and prase]

Most commonly we encounter this gem as translucent cabochons or carvings in its apple green color.

[Cabochons and carvings of fine quality chrysoprase]

The appearance of the best colored pieces is similar to that of fine jade, and explains the high regard this stone inspires in the Orient. In fact, unscrupulous sellers of both contemporary and vintage jewelry have been known to sell chrysoprase as the more valuable jadeite. Looking at the two rings below, it is not immediately obvious which is chrysoprase and which is jadeite.

[Chrysoprase ring, jadeite ring]

A rare, related chalcedony in darker, less saturated shades of green, that is colored by chromium occurs in Zimbabwe and is called Mtorolite, but sometimes is sold as "African chrysoprase".

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[Mtorolite chalcedony from Zimbabwe]

Like other forms of chalcedony, chrysoprase makes a good, tough, gem for all jewelry applications. The only concern is that some specimens may lose a bit of their color if they are exposured to prolonged high heat or intense light. Chrysoprase, itself, is not known to be treated or enhanced; however dyed green agate, and green glass have been commonly used as simulants. Value With the exception of the finest grades of chrysocolla chalcedony, chrysoprase is the most valuable variety among the chaledonies. The most desirable gems in this material feature an even, highly saturated color with substantial translucency and no visible inclusions. Custom cut specimens are more valuable than calibrated cuts and larger pieces of high quality are rare.

Gemological Data: Makeup: Silicon Dioxide Luster: Vitreous to waxy Hardness: 7 Crystal structure: Trigonal Fracture: conchoidal Cleavage: none Density: 2.61 RI: 1.53-1.54 404

Birefringence: .004 Pleiochroism: none

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Quartz with Inclusions Why would anyone want a gem with inclusions? Generally the more inclusions in a gem, the lower its value. This is particularly true if these inclusions discolor the gem, degrade its transparency, or make it more likely to fracture. Strangely enough, there are numerous gems whose value is enhanced by the presence of inclusions, which either identify its species or origin, or give it certain optical or color characteristics. Examples would include demantoid garnet whose "horsetail" inclusions verify valuable Russian origin, sunstone whose reflective platelets give it sparkle, Baltic amber with trapped insects or plant parts, and star rubies and sapphires which depend on included rutile needles for creation of the star phenomenon. Value Raising Inclusions

[Bryssolite asbestos "horsetail" in Russian demantoid, sunstone with hematite platelets, insect in Russian amber, star ruby.] This short discussion, however; will focus on just one species: quartz, and some of the inclusions which can give it added value. Rutile The most common and familiar inclusion in quartz is rutile. The needle-like crystals can be thick or thin, pale gold to rich orangey brown and arranged in dense or sparse patterns.

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[Rutilated Quartzes] What might be considered the "Holy Grail" for quartz inclusion collectors is the rutile/hematite starburst. In these pieces a six sided, shiny black hematite crystal serves as an alignment point for the rutiles which, in the best examples, line up in parallel bundles along each face forming a six rayed star with a hematite center. Such pieces are sought after and highly valued even when the stars overlap or are incomplete.

[Pendant with near perfect rutile/hematite starburst, partial starbursts] Other Needle-like Inclusions Other needle-like crystals such as edenite, Goethite, and tourmaline produce attractive and interesting gems with various colors and patterns.

[Quartzes with green edenite, golden Goethite needles in "sheathes" and tourmaline inclusions] The tourmaline crystals are most often opaque black and are particularly desirable when they occur as large isolated individual crystals. One sought after type of this gem is a round faceted quartz with a single black 407

tourmaline needle captured in it--> if it runs from the center of the table to the culet it will reflect in all the pavilion facets and form a perfect "pinwheel".

[Tourmalinated quartz "pinwheel" from front showing multiple spoke-like reflections, from side, showing single central needle] Not Only Needles Besides the needle-like crystals there are other types which create attractive interior landscapes. For example, pyrite with its metallic silvery-gold color can occur as random shapes, as "flowers" or "suns" or, most sought after, perfect cubes! Platelet-like forms of red hematite or lepidocrosite can give an overall pink or red color to a clear quartz as in the strawberry and raspberry quartzes. Some materials, such as manganese oxide, form crystal "dendrites" within quartz which look like snowflakes, fern fronds or tree branches. Many newcomers to the gem hobby have mistakenly taken these to be fossil plants within the stone, as the form is so realistic.

[Quartzes with pyrite "suns", perfect pyrite cubes, strawberry quartz with hematite platelets, dendritic quartz with manganese oxide dendrites] 408

Growth Phenomena Growth phenomena such as starts and stops during crystal formation sometimes provide interior interest. "Phantoms" which show the outline of a host crystal face with deposited material of a different color or transparency, and "negative crystals" which are voids bounded by the growing host crystal walls are examples.

[Quartzes with edenite phantoms, landscape of negative crystals] One of the most interesting quartz inclusions for the collector to own is an "enhydro". This is the case where a bubble of gas is trapped within a pocket of liquid inside the crystal. As the piece is tilted, the bubble freely moves within its chamber.

[Quartz with moving "enhydro" in different positions as the stone is tilted] Non-transparent Quartzes Certain microcrystalline quartzes, the chalcedonies, also can be improved by their inclusions. Examples include dendritic chalcedony with its flower-like patterns, "amethyst sage", and the iron stained channels of Indonesian chalcedony which create random (but sometimes meaningful) patterns. Such inclusions can be microscopic as in the case of chrysocolla in quartz (gem silica) which gives a tough-as-quartz gem with the sublime color of the much more fragile chrysocolla. 409

[ Dendritic chalcedony, "amethyst sage", Indonesian chalcedony, "gem silica"]

[Indonesian chalcedony alphabet] Quartzite Rock Crystals of metals like gold, silver and copper within white quartzite rock have long been valued for their beauty.

[Gold in quartz ring and bolo tie, copper in quartz pendant] Synthetics and Simlants/Care: In general, simulants and synthetics of these gems are rare, prices are reasonable, and fragility is not a problem, so there is little to worry about. Collecting or wearing pieces with interesting internal features such as these can increase one's enjoyment and appreciation of gemstones greatly.

Value Factors 410

When considering the purchase of an included quartz, the main factors to consider would be the distinctiveness, rarity and beauty of the inclusion(s) within the stone. In addition, it is usually true that the more centrally placed and the less obscured by extraneous inclusions the desired ones are, the higher the value. The general factors of value for any stone such as clarity, carat weight, color and cutting perfection would provide secondary value points.

Gemological Properties Makeup: Silcon Dioxide (plus make up of inclusions) Hardness: 7 Toughness: good Crystal System: Trigonal Luster: Vitreous Density: 2.61 (inclusions generally increase this) RI: 1.53 -1.54

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Rubellite Tourmaline Rubellite is the name given to dark pink to red tourmalines, especially those with reasonably saturated colors and medium to dark tones. Ruby red stones with little orange or brown overtones are the most highly sought after. GIA has traditionally classified rubellite (along with Emerald) as a Class III gem, meaning that it is almost always included. This is somewhat less true in recent years as deposits from certain regions of Africa yield much cleaner rough. Alas, these stones, so often tinged with brown, almost never approach the ruby like color of the best of those from older, more included, Brazilian deposits. Russia, Brazil, Madagascar, Nigeria and the US are productive sites for this gem.

Natural pink to red color is created by trace amounts of manganese in the chemical composition. Cat's eye stones are sometimes available. Irradiation, in some cases with heating, is a now common practice, and can produce stable red tones in otherwise pale pink stones. As this practice is undetectable all stones must be presumed to be treated even though this may not be the case for an individual stone. Highly included rubellites are sometimes treated with fillers similar to those used on emeralds. This treatment, however, is detectable by standard

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methods. All tourmalines make excellent jewelry stones and require no special care.

Value Due to scarcity and beauty, the most valuable pieces are untreated, clean (eyeclean or better) deep pinkish red to slightly purplish red stones. Those with light pink color are sometimes offered as rubellite, but more properly should be labelled pink tourmaline. Brownish tones decrease value considerably. A custom cut adds value, although the majority of Brazilian pieces are native cut. Gemological Data Makeup: a complex borosilicate Luster: Vitreous Hardness: 7.5 Crystal structure: Trigonal Fracture: conchoidal Density: 3.06 RI: 1.62 - 1.64 Birefringence: .018

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Aventurescent Gems When a gemstone contains large numbers of disk-like or platy inclusions that have a metallic or highly reflective surface, aventuresence is the result. In good light, the visual effect is reflective speckles and sparkles, from subltle to dramatic, depending on the type of inclusions and the color and transparency of the host mineral. The little mirrors responsible for this effect can be green fuchsite mica, reddish hematite or Goethite, or metallic copper. Glass The name of this phenomenon derives from an Italian word meaning "chance" or "accident" and is said to have first been used to describe manmade goldstone glass. The (probably apocryphal) story, is that a worker in a glass factory accidently spilled a bucket of copper filings into a batch of molten glass. The resulting "aventurine" glass, was so pretty that the factory began making it deliberately. Only later, as the story goes, did gemologists borrow the term to label Nature's own glittery handiwork.

[Man-made "goldstone glass", close up at 10x] Quartz Only two species of gemstones are commonly seen in aventurescent form: quartz and oligoclase feldspar. The quartz gems, are known as aventurine quartzes (not adventurine as I hear some of the home shopping channel hosts call them!) and occur naturally in reddish (hematite), and more commonly, green (fuchsite) shades. The effect is more speckly than glittery in most pieces, but pleasing, nonetheless. Aventurine quartz is a porous material and takes dye easily so that it commonly is offered in dramatic and (to my eye) unnatural looking colors. The most common use for this inexpensive stone is as material for cabochons, beads and simple carvings. 414

Fine grades of aventurine quartz have been used as jade simulants in high quality carvings, and can be visually convincing.

[Natural color aventurine quartz carving, dyed green aventurine quartz]

[Red aventurine quartz beads] Feldspar Feldspar gems that show aventuresence are called sunstones. They range from opaque through translucent to nearly transparent, depending on the locale, the inclusions and their density. Until recent decades the world knew sunstone only as an opaque coppery material from India. These pieces superficially look a lot like goldstone glass.

[Indian sunstone cabochons] At present, the most popular form of sunstone is that from Oregon, USA, which ranges from straw colored transparent stones without aventurescence to transparent pieces in a range of body colors both with and without copper platelets. The metallic shimmery display is commonly referred to as "shiller", although technically that term is more appropriate for the displays seen in Labradorite and moonstone.

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[Faceted Oregon "shiller" sunstone, 10x closeup of a similar gem] The most recent aventurescent feldspar to make a splash in the market, is that from Tanzania, which has hematite and/or copper inclusions. Both transparent and translucent pieces are available and in the best specimens the phenomenon is multi-colored.

[Tanzanian sunstone carving,"confetti"sunstone] Other Species Occasionally, other gemstones exhibit aventurescence, such as members of the mica group like the lavender colored lepidolite, or rocks containing fuchsite mica. An extremely rare gem, sought avidly by collectors, is a variety of iolite with hematite inclusions with the colorful name of "bloodshot iolite".

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[Lepidolite, ruby in fuchsite, bloodshot iolite] Value Factors The value of aventurescent gems ranges from extremely modest to rather costly with Indian sunstone and aventurine quartzes on the low end and fine Oregon shiller-sunstone (especially those with red body color) at the top. In general, the individual value of these stones follows the traditional factors which create value in all gems: size, color, cut and, with the exception of the phenomenon-causing inclusions, clarity. Added to these would be the beauty of the aventurescent display -- the more reflective the better.

Gemological Data: Varies with species

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Chatoyant Stones The most commonly appreciated expression of the chatoyance phenomenon is in the formation of cat'seyes and stars. When fibers, needles or channellike inclusions within a gem align themselves parallel to one or more crystal faces and the gem is cut in the proper orientation with a moderate to high dome, a cat'seye or star figure appears. I've covered both of these in other essays, so in this writing I want to focus on those cases where the phenomenon is less organized. When the parallel inclusions are oriented in patches, or not aligned with a crystal face, or when the gem is not cut so as to orient them, the result is a silky surface sheen simply called chatoyance. You can visualize the effect by comparing the reflections you'd see in silky thread wound on a spool versus that same thread wound around a flat card. The dome created by the spool concentrates the reflections into a band ( cat'seye) whereas the effect on the card is merely a generalized silky glow.

The most well known and available gem with this effect is tiger'seye and its bluish relative hawk'seye. Until just recently, tiger's eye was thought to be a "pseudomorph" meaning a mineral in which crystals of one material take on the form of another. Tiger'seye, in virtually all current gem books is called a chalcedony pseuodomorph of crocidolite (a form of asbestos). I was quite surprised a while back to find the lead article in one of my science magazines devoted to new information on the structure of this popular gem. It seems that rather than chalcedony replacing crocidolite, this gem is actually a combination of crocidolite and layers of crystalline quartz (Science News, 4/26/2003). Of course it still looks the same, but I find it intriguing that after 130 years of authors writing about this gem in popular articles and gem reference books, new information can still be derived.

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[Tiger'seye cufflinks, pair of tiger'seye carvings, hawk'seye cabochon]

[Tiger iron, Pietersite] As the gem forms it is generally a blue-grey-green color, but when subjected to oxidizing conditions the iron in the crystals turns gold. Such conditions are common geologically, making the golden form much more prevalent than the blue. Enhancement by man has created "super-oxidized" pieces which are orangey red, and there are some garishly dyed pieces on the market as well. Closely related gems are tiger iron, which is a combination of jasper and tiger'seye, and Pietersite, which is a brecciated tiger'seye and/or hawk'seye. Many other gems show varying degrees of chatoyance, including some corals, Amazonite, Charoite, serefinite, sapphire, ruby, and Smithsonite.

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[Alaskan coral, Charoite, serefenite]

Value Considerations Aside from the overall rarity and quality of the gem in question, the degree of the chatoyance phenomenon would be the most important value setting aspect, with those displaying it more fully are considered more valuable.

Gemological Properties: Vary Depending on the Species

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Star Stones (Asterism) When parallel, needle-like inclusions, or tube-like channels, are oriented along two or more of the crystal faces of a mineral, and when that stone is cut as a domed cabochon, a four to six rayed figure is displayed on the dome. This phenomenon of reflected light is called "asterism" and the gems are called star stones. The most commonly seen examples are star corundums; where there are inclusions of titanium oxide (rutile or "silk") parallel to three crystal faces giving a six rayed star. In rare cases a twinned crystal slightly offset with its own set of rutile needles can lead to the formation of a twelve rayed star. Although rutile is an extremely common inclusion in sapphire, few good, natural, star sapphires are found. One of the major reasons is that the heating which is almost universally done to sapphire rough, dissolves rutile needles, clarifying and sometimes color enhancing the stone, yes, but eliminating potential stars!

[Rutile needles (silk) aligned in three directions in unheated corundum]

[Star ruby, white star sapphire ring, rare bi-colored star sapphire]

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The only other gem which commonly forms stars is quartz, where the phenomenon tends to be more visible in transmitted than n reflected light, in this species, rose quartz is the most frequently asterated variety. Most citrine in commerce has been heated which tends to dissolve the fine rutile inclusions necessary for star formation, so it is rather rare. In fine, near transparent quartzes which have been cut to near spherical shape, multiple stars can form an intersecting pattern over the surface.

[Star rose quartz, star citrine, multi-star quartz] Synthetic star corundum has been produced for many decades in a process whereby a high concentration of very short rutile fibers are added to the crucible as the raw materials are melted, and the resulting crystals are cooled in a very controlled manner. Such "Linde" sytle stars look extremely uniform and bright--->they almost seem painted on the surface rather than to emanate from within the stone. In more recent years, diffusion processes have been developed by which natural gemstones (almost always corundum) can be star enhanced. In contrast to unenhanced, natural star gems these diffused pieces, like the synthetic ones, have stars which are stronger, straighter and appear less mobile, and are more confined to the surface.

[Synthetic "Linde"- type star ruby, a diffusion enhanced, natural-origin star sapphire]

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Other much less commonly found star stones include diopside, enstatite, moonstone and garnet which show four rayed stars and beryl and spinel which usually show six rayed stars.

[Star diopside, star moonstone, star garnet: Image courtesy of GIA, star spinel] In some cases natural patterning, color zones due to twinning, or inclusions can form a four or six sided figure in the a stone, but as these are not dependent on light for their existence, and are a permanent part of the gem, they are not considered star stones.

Not Star Stones!

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[Rutile-hematite starburst in quartz, inclusion stained channels in Indonesian chalcedony, chiastolite: Andalusite crystal with carbon inclusions, trapiche emeralds--small emerald crystals outlined and adhering to each other due to carbon inclusions ] Star stones are usually native cut and often have bulging sides and an uneven bottom which can complicate the setting process for jewelers. Rather than this indicating lack of skill or care, we should consider that native cutters are very skilled at maximizing the star potential of any piece of rough. Depth in the bottom of the stone can increase the clarity of the star and controlled unevenness can often help center the star in rough that is difficult to orient. Speaking in terms of corundum and quartz, star stones have good wearability and are often chosen for rings. When choosing a star stone for your collection or for jewelry wear, it is important to remember that the star you see is a function of the quantity, direction and quality of available light; and it will show itself to best advantage only in strong light, such as sunlight or a single overhead light source indoors, especially when that light is perpendicular to the base of the stone. Under dim, diffuse or multiple light sources, or if held vertically or at extreme angles, all but the very strongest star stones will merely look chatoyant.

Value Factors Several factors influence the value of star stones. First would be the rarity of the material itself. For example, star beryl or star spinel have inherent rarity value not possessed by star quartz or corundum, since these species so infrequently form stars. Secondly, within any gem category value rises with the same three basic parameters that control most of any gem's value: color, clarity and carat weight. In general, the more saturated the color, the more translucent, the fewer distracting, visible inclusions, and the larger the size, the more valuable a star stone is. Added to these basics are the characteristics of the star itself. The best pieces have strong stars which show themselves in less than ideal lighting conditions. These stars have straight, evenly bright legs which reach all the way to the girdle of the stone and are well centered in the gem.

Gemological Properties: (Values are for sapphire -- will vary with gem species) 424

Makeup: Aluminum oxide Hardness: 9 Toughness: Good Crystal System: Trigonal Luster: Vitreous to silky Density: 4.00 RI: 1.76-1.77 Birefringence: .008

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Color Change Stones One of the most interesting of the optical phenomena to be seen in gemstones is color change. This characteristic is sometimes confused with pleochroism, where a stone shows different colors when viewed down different crystal axes, such as in Andalusite and iolite. True color change, however, exhibits itself as a color difference over the whole stone when viewed in different light sources. Typically one color is seen in incandescent light, a source which is rich in red wavelengths, and another in fluorescent or natural daylight sources which are rich in the blue end of the spectrum. The most famous gem of this type, and the one to which all others are generally compared, is Alexandrite (the color change variety of the species chrysoberyl). The finest specimens from old Russian sources, which are virtually unobtainable in today's market, switch from near ruby red to near emerald green with a change in the light source. Present sources of Alexandrite, which ranges from poor to good in quality are India, Sri Lanka, Madgascar and South America. (The faceted stones below are from Sri Lanka, and the cat'seyes from India). Alexandrite

Daylight

Incandescent Alexandrite Cat'seye

Daylight

Incandescent

Under certain conditions, when a gemstone contains a chromophore which reacts very selectively and strongly to red wavelengths (such as chromium) different body colors can be produced due to the richness of reds in incandescent light and their relative scarcity in either daylight or fluorescent 426

light sources. Depending on the other elements present, various combinations of colors and strengths of the effect will be seen.

[Comparison of the spectrum from daylight and most fluorescent sources versus that of an incandescent lamp: Graphic courtesy of www.nasa.gov] The three species most usually sold in color change forms are: chrysoberyl, sapphire and garnet. Many other gemstones may show the effect to a greater or lesser degree including: diaspore, tourmaline, spinel, iolite, and beryl. There are many global sources for these stones such as Turkey, Brazil, and various African countries.

CC Garnet, Daylight

CC Garnet, Incandescent

Synthetic color change stones have been available nearly as long as synthetics themselves. First among these was color change synthetic corundum marketed as "Alexandrium" with true synthetic Alexandrite being a more recent addition.

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Metamerism is the general phenomenon of two colored object appearing to be slightly different hues depending on the light source, and it is by no means confined to gemstones. Although almost every colored gemstone will look slightly different indoors and outside, but we only call it "color change" when the difference is realtively dramatic. Metamerism of this subtle type is a factor that a jeweler must to take into account when attempting to match gems for a setting or in finding a replacement for a missing gem. Customers can be very unhappy when the gems match perfectly indoors but not outdoors or vice versa.

Value Fine Russian Alexandrite is at the apex of all color change stones in terms of both quality and value. Alexandrite from other sources such as Brazil, India and Sri Lanka varies in price depending primarily on the saturation of the colors, and the strength of the change. Other color change species are available at more modest prices, which for fine sapphires might reach into the same range as non-Russian Alexandrite, with the best grades of color change garnet somewhat lower. No established price ranges for most species are found as specimens are few and generally go to collectors. As in all gems, size, clarity and color affect value, but with this group there are two additional factors: completeness of the color change and the attractiveness/saturation of each color. A stone with a modest color change having two saturated and attractive colors may be as valuable or more valuable than one whose change is more dramatic but whose colors are greyed or browned. Gemological Data This varies with the species but does not vary, from the non color change forms of the same gemstone.

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Iridescent Gems Due to their internal structure, a number of gem varieties show a surface or interior display of colors which are not part of the gems themselves, but rather created by the behavior of the light that enters them. This optical phenomenon, called iridescence, is familiar from everyday situations like the colored layer that oil or gasoline make on a puddle of water, or the rainbow effect we might see on the surface of a CD. Both diffraction and interference play a part in the effects we see. In the case of color play in opals for example, the gem's ultrastructure based on uniformly packed spheres of cristobalite silica acts like a diffraction grating which breaks light into the various wavelengths of color. As they reflect from the various inner layers, the now, slightly out of phase waves combine and subtract by interference, and we see blocks of spectral colors. The size of the internal spheres determines the color: with mostly smaller spheres: we see blue, with mostly larger ones: we see red. Beyond a certain sphere size, as in common opal, light doesn't have to bend to travel through the openings, so no color play is seen.

[Common opal: no color play, precious opal: with color play] In most of the other iridescent gems an ulrastructure of thin layers acts to create the color-making for diffraction and interference. One of the most highly valued gems of all time, pearl, gets its surface iridescence or "orient" from a subtle interference created as light travels through the thin layers of partially crystalline nacre. Mother of pearl and gem shell materials sometimes have intense color displays as well.

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[Baroque freshwater pearl, South Seas black pearl, abalone blister pearl] Labradorite is a form of feldspar that is noted for its iridescent optical phenomenon. In this gem in general, and in its more colorful variety, spectrolite, the iridescent effect is usually confined to a single direction, and is created by repeated thin laryer internal crystal twinning.

[Labradorite carving, spectrolite cabochon] Some of the most beautiful less common gems, owe their striking colors to iridescence as well. Ammolite, a fossilized shell, which shows iridescent colors over a brown or dark grey shell matrix is rapidly gaining popularity as is fire agate, a form of iridescent botryoidal chalcedony.

[Ammolites: blue and red]

[Fire Agate] VALUE CONSIDERATIONS All else held constant, the stronger the phenomenon of iridescence the more valuable the gem. In opals, larger patches of color, greater saturation of 430

color and more individual colors are more desirable than tiny points or single colors. In pearls, a thicker nacre coating creates a more visible and even display of orient which increases their value. Ammolites increase in value with the amount of blue and violet, in their displays, as red, green and gold are more common and the situation is very similar with fire agates. The degree to which the phenomenon covers the entire surface is a strong value factor, with "dead" spots detracting substantially from value. Another factor is the degree of directionality of the phenomenon. All Labradorites and some fire agates and ammolites, for example have a single plane or a limited few angles at which strong colors show and at other angles this effect fades. As with any gem, body color, clarity, size and beauty of the fashioning are additional factors which influence price.

Gemological Properties: Varies with species

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Cat'seye Stones Chatoyance is the term for shimmering or silky reflections seen on the surface of a gem. This effect is created by light reflecting from fibrous inclusions. When these inclusions are parallel to each other and occur in sufficient quality and quantity, and when the gem is cut so as to align them properly, then a single reflection centered on the cabochon dome is formed which is referred to as a cat'seye. Many gem species have cat'seye varieties, including (but not limited to ) apatite, actinolite, beryl, chrysoberyl, Kornerupine, tourmaline, quartz, sillimanite, moonstone, opal and zircon. A related phenomenon, asterism, or star effect, is created when the parallel fibers lie in different crystal planes relative to each other and is really just a case of 2 or 3 centered cat'seyes visible at the same time. The finer and more completely aligned the fibers, the stronger the cat'seye effect will be. The shape of cat'seye stones is nearly always round or oval and the cabs are generally cut with a high dome. All other factors being equal, the higher the dome of the cab, the stronger the eye. As the cat'seyes of antiquity, only chrysoberyl cat'seyes are properly referred to as "cat'seye" with no modifier. Especially popular in the Orient, both the darker "honey" and lighter "lemon" colors are popular. Traditionally men have favored honey and women, lemon. All other species of cat'seyes should be given varietal designations like cat'seye tourmaline, cat'seye scapolite, etc. Sunlight or a single overhead light source produces the best effect, and new owners are sometimes disappointed that the eye that they saw so clearly in the photo or in the showroom can't be seen clearly in dimly lit rooms or in those with multiple, diffuse light sources, like overhead fluorescents. Savvy buyers of these stones often carry a penlight to check out the sharpness of the eye of stones they are considering. Some pieces show a highly desirable effect referred to as "milk and honey" where cat'seye gems lighted from the side split into a light and dark half. Also occasionally seen is the "opening and closing" effect where pinpoint light sources held above and then pulled apart to light both sides, causes the eye to split into two lines which follow the light sources. The vast majority of cat'seye gems have been native cut with uneven bottoms, but this is not necessarily a sign of haphazard work or poor lapidary skills. Specialists in cutting these gems are great masters at 432

revealing and centering an eye, which frequently necessitates such unevenness. Care should be taken in setting such as stone to provide cushioning and leveling material underneath.

[Honey and lemon colored cat'seyes, cat'seye apatite, cat'seye Kornerupine]

[Cat'seye aquamarine pair, cat'seye scapolite pair, ultra-rare cat'seye Pezzottaite (beryl)]

Value The value of a cat'seye gem is, related to both the inherent value of the gem species, and the fineness of the cat'seye display. The most highly valued species is chrysoberyl, with large transparent, top quality gems commanding several thousand dollars per carat; while even the finest quality cat'seye quartz can be had relatively inexpensively. In general terms, rich color, high transparency and distinctness of the eye enhance the value. Milk and honey effect and opening and closing of the eye also raise the value of a cat'seye stone. Gemological Data: Properties will be within the same ranges as the non-chatoyant varieties of that species

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CONSIDERING FACETING?

[Your instructor's well used machine]

Do You Want to be a Facetor? Have you been considering learning to facet? Although there are many attractive aspects to this craft, there are also some cautions; it's definitely not everyone's cup of tea. Faceting machines are pricey and the wise individual will think carefully about whether this hobby will suit him/her, before jumping in with both feet. Is it Right for Me? From my perspective, there are five major ways in which faceting makes an excellent pastime. 1) Faceting is nicely flexible time-wise, in contrast, some hobbies such as baking, require that you finish the project once it is started. Not so with faceting, while some speedy and dedicated cutters finish more than one piece a day, others may enjoyably work on a single stone off and on for months, as time permits. 434

2) It is very interesting. There's enough technical knowledge required such that faceting presents a pleasing challenge with ever expanding horizons as new materials and cutting techniques are incorporated into one's repertoire. 3) Your activities are not confined to a certain season or locale as with fishing or gardening, nor is the equipment so large or messy as to require a special workshop. 4) Faceting can lead to acquaintance with a new group of friends that share your interest, and can help you solve problems you might encounter in the learning process. These can be found at a local rock and gem club, a regional facetor's guild, or on the internet. 5) Bottom line, one of the most appealing rewards of the faceting process is the finished product! The thought of gaining the knowledge and ability to take a piece of gem rough that looks something like driveway gravel, and turn it into a sparkling treasure is all the incentive and inspiration most "would-be" facetors need. On the down side, faceting itself is pretty much of a solitary activity, and as such, can lead to resentments from family and friends who are feeling left out as you hunker over your machine, hour after hour. And on a practical note, the expense of getting started in this activity can run to several thousand dollars. Maintaining your "habit" with new rough, books, supplies and gadgets will place a long term drain on your income. Am I Right for It? Many who are considering getting started in this craft wonder if they have the requisite characteristics to make a good facetor. The physical requirements are few, but you do need enough manual dexterity to handle the gems, and enough strength to work the machine. (Don't worry too much about these criteria as one of the best facetors I ever knew was missing a thumb on his right hand, weighed 90 pounds and suffered from emphysema!). You'll also need reasonably good vision (with correction); but even here, the requirements are eased by the fact that you'll be wearing a magnifying headpiece as you cut. Faceting, as an activity, is virtually "ageless". Successful cutters range from pre-teenagers to nonagenarians.

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Personality traits conducive to successful faceting are: patience (some parts of the process are repetitious); attention to detail, and the ability to keep your cool when things go wrong. What you don't need is: creativity (unless you intend to design new cuts); a degree in geology or gemology, or an engineer's level of mechanical ability. None of these attributes would be detrimental, of course, but they aren't, in the least, essential to enjoying and succeeding in the faceting process. OK, I want to try it, What do I do first? If a person has decided they want to give faceting a try, how should they go about it? The worst approach would be to look through a magazine like Rock and Gem or Lapidary Journal, find an ad placed by a faceting machine manufacturer, make a call and order everything from A-Z. You REALLY need to try the process "hands on", before spending any money. I've known more than one individual who bought before trying, and then sold their equipment, at a loss, after they decided they didn't like faceting after all. How can you try it? The very best situation would be to go to a faceting school, but only a few of those are available and they, too, are expensive. Better to try it out at the side of an experienced facetor, kind of like an apprenticeship. Your local chamber of commerce or city or county website can give you the contact name, email or website address and/or phone number of any gem or lapidary clubs in your area. Attend a meeting, and introduce your self to a facetor. Most of them remember how they got started and are willing to at least demonstrate (if not teach) the process "one on one". Alternately you could attend a gem show, where there usually are faceting demonstrations taking place. The "demonstrator" is a possible mentor who might let you get your hands on a machine. If neither of those avenues yields a tutor, then you can order video tapes of the faceting process from several companies. Try an internet search on "faceting video" or look through the ads in a lapidary magazine for sources. At this point you will at least know what faceting is like. If you've passed this hurdle, and knowing what is involved, still want to jump in, it's time for research. There are a number of good beginners books in the field of faceting, with Edward Soukoup's The Facet Cutter's Handbook, being the least expensive. More inclusive is Glenn and Martha Vargas' Faceting for Amateurs, which will remain useful, long after you've 436

passed through your newbie stage. If you've read these books, or others, and STILL are interested, now's the time to buy your equipment. Getting The Equipment to Begin Faceting Here's the scoop on machines--> they're all good! That being said, it's still true that non-biased assessments are very hard to find as all facetors tend to think their own machine is superior to other brands. You may be lucky enough to run into a deal on some used equipment, but let's say you are going to buy new. Where do you start? It would be useful to write or call the major manufacturers (most have websites and all advertise in lapidary magazines) and have them send you their information packages. The old joke about faceting is that the most important piece of equipment in faceting, is the big thing sitting in front of the machine! It's kind of like with autos, either a Chevy or a Lexus can get you from point A to point B, especially if you are a good driver (and of course a bad driver can wreck either one). Differences in bells and whistles, and ability to keep in adjustment reliably without numerous trips to the repair shop, equate to differences in price, but all machines on the market will do the job.

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Less Common Organic Gem Materials There are five groups of organic gems that are most often encountered in the gem and jewelry marketplace, or studied in gemology classes: pearls, amber, coral, ivory and jet. Pearls, amber, and coral are presently a major part of gem commerce (although the overfishing of coral is beginning to show). Ivory and jet are less common, and are most often seen in vintage or antique pieces. As all five have been covered in some detail in previous essays, it is my aim here to survey some of the rarer and/or lesser known organic materials that are currently, or have in the past been used for jewelry purposes. In truth, some of the items listed here, fail to meet the "durability" criterion required for definition as a "gemstone", but have nonetheless been included due to historical interest or, to be honest, just because I think the're cool. :-) Teeth/Tusks Technically, teeth or small tusks are considered "ivory", but except for that from elephants and walrus few such items, are seen today. Many types were popular historically though, particularly in the Victorian Era. Rarer ivories include sperm and killer whale teeth, hippo teeth and perhaps most exotic, narwhal tusk. Trade in tooth and tusk ivory varies in legality depending on the species, the country of sale, and the age of the piece. Sale of boar tusks, and hippo teeth, for example, are unrestricted, whereas trade in whale, walrus and narwhal ivory is limited to native populations or certified antiques. Ivory artifacts are relatively durable due to their density and relatively high ratio of mineral to protein components.

[Victorian Era boar tusk pin, example of "previous owner" ]

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[Vintage elk tooth ring set in gold with diamonds, polished and scrimshawed slice of narwhal tusk ivory] Claws, Horn, Hair and Related Materials Structurally, this grouping has in common the presence of at least some keratin protein. Hair and claws are virtually all keratin while, horn, tortoise shell and antler vary in the degree to which the protein component has been "mineralized". Claws Certainly our remote ancestors made use of animal claws in their jewelry, but not too many examples have been prominent in Western culture in the last couple of centuries -- particularly not in settings of high karat gold. A notable exception to this is "tiger claw" jewelry seen sometimes in the antique market and hotly pursued by collectors. During the British colonial period in India, the wild tigers which are, so rightly, strictly protected in today's world, were seen as vermin of a particularly threatening kind. The "Sahibs'" tiger hunts were, at least to read British-authored historical accounts, much encouraged and appreciated by the native population. Taxidermists mounted heads, furriers made pelts, and jewelers set the claws in brooches and pendants.

[Tiger claw brooch in high carat gold, Victorian era: Image courtesy of www.fraleigh.ca] Horn

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Horns from various species have been well known from both historical and current times as the source of useful objects such as cups and storage containers and handles for implements. In the jewelry world, horn is most often encountered in either the least expensive of tourist trinkets, or as an imitation of rarer materials, like jet or tortoise shell.

[Dyed horn brooch, circa 1930 simulating jet] Antlers Antlers (which are conveniently shed yearly) have long been used for utilitarian and decorative purposes -- even the most casual collector of knives has at least one with antler adorning the handle or hilt. Antler has a ridged structure which makes it distinctive. The antler base, sometimes called the "button" or "flower" has also been used decoratively.

[Antler, a renewable resource!, bolo tie with jasper, an antler "button" and antler tips] Hair Human hair has in various times and cultures been used for jewelry purposes, but never as artistically and enthusiastically as in the US and Great Britain during the Victorian period. Perhaps you'd feel a bit squeamish about touching or wearing a vintage jewelry piece made from a dead person's hair. This was my initial reaction, but with time I've done a complete turnaround, and become an avid collector. Pieces range from simple locks of hair behind glass, or in a locket compartment, to elaborately 440

woven works, and even "paintings" using strands of hair as the medium. Books of instructions and patterns for "hair work" were popular with young women of the time, and looms and other implements were sold to aid them. Such jewelry items were given as gifts between young lovers, or worn as remembrances of loved ones who had passed away. It was indeed a more sentimental age than ours.

[Hair work jewelry: all items circa 1850 -1900, intricately woven hair brooch in 14k, gold, enamel and hair brooch (and close-up showing that two kinds individuals contributed (the dark hair makes a woven background, for the knotted blonde hair), a multi-strand hair work bracelet showing several different patterns of weaving and closeup] Human hair is not the only type found in jewelry. Those same British colonials who were sending home tiger claws in jewelry, also valued elephant hair (yes, that is a single hair!) in bracelets, necklaces, and rings.

[Elephant hair ring] Tortoise shell Although we use the term "tortoise shell", in reality the carapace of a turtle or tortoise is actually not a bit like the shell of a mollusk, but is chemically 441

and structurally most similar to horn. The term tortoise shell has come, in modern times, to stand more for a color pattern than a gem, and is seen almost exclusively in plastic imitations. As they should be, the hawksbill sea turtles which are the source of gem tortoise shell are a protected species in today's world, but down through history their shell was used for furniture veneer, household implements, and hair ornaments as well as for jewelry.

[Tortoise shell brooch and bracelet circa 1930's] The natural thermoplastic properties of tortoise shell made possible a unique art form which dates back to the 1700's called "pique". Pieces of silver or gold were heated and pushed into a piece of tortoise shell, which would then shrink around the metal as it cooled, holding it in place, enabling the production of simple to amazingly complex patterns.

[Tortoise shell 14k and sterling pique brooch, circa 1850, pique earrings, circa early 1800's: Image courtesy of Arlene Nobel Antiques] Baleen Whales are divided into two basic groups depending on their feeding mechanism, called the toothed and the baleen whales. Baleen whales feed by 442

straining huge mouthfuls of water and extracting small crustaceans and other edibles. Their "strainers", called baleen, hang from the upper jaw and can be yards long. Each fringed plate is made of a flexible proteinaceous substance very similar in composition to horn or tortoise shell. Baleen historically had many industrial and domestic uses (including the "whalebone" in lady's corsets), but it was, and still is, used for art objects and jewelry. Presently, only Native Americans whose traditions include whaling can legally harvest and use these whales' parts, including baleen.

[Small baleen plate in its natural state, circa 1900 scrimshawed raw baleen plate, contemporary scrimshawed baleen brooch] Hornbill "Ivory" One of the rarest of all organic gem materials is known as "hornbill ivory" or golden jade, but it is neither ivory nor jade. It is a proteinaceous horn-like material obtained from the "casque" or secondary bill, of the Kenyalang or Helmeted Hornbill bird from Borneo, now rigorously protected. Only certified antiques such as those below can legally be traded. In earlier centuries this material which ranges from a creamy white to translucent golden yellow was used for ornamental and jewelry purposes particularly throughout the Orient. Most valued was the outer "rind" of the bill which was stained a bright red-orange from glandular secretions rubbed into it by the bird's preening activities.

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["Helmeted Hornbill": Image courtesy of Sarawktourism.com, antique hornbill ivory netsuke carvings: cicada and "fat boy stealing the peaches of immortality"] Pearls that are not Pearls What we commonly call pearls are irritant-induced secretions of mollusks which are covered with lustrous nacre (a combination of aragonite or calcite and conchiolin protein). They were once highly valued products available only from Nature, but the 20th century and Mr. Mikimoto, the cultured pearl king, changed all that. Humans now routinely force certain species of captive oysters and mussels to produce gem pearls. Other mollusks, however, form substances loosely referred to as "pearls", but technically known as calcareous concretions, as they lack nacre. Gem quality nonnacreous pearls (conch pearls, scallop pearls and melo melo pearls) are rare collectors items which have their own unique beauty. They have a shiny, porcelain-like surface and are produced in various shapes and colors. By far the rarest (although to my eye not the most beautiful) are the marble and larger sized pearls from the giant baler or melo melo snail -- a fine specimen can bring tens of thousands of dollars! Non-nacreous pearls

[Non-nacreous "pearls": conch pearl, scallop pearl, melo melo pearls: Image courtesy of www.gemsfromearth.com] Opercula 444

An interesting oddball jewelry item, sometimes called the "Pacific Cat'seye Pearl" is likewise not a pearl, but a calcified protein secretion of a South Seas snail known as the Turban shell. Technically it is called an operculum and functions as a kind of "trap door" to seal off the snail's soft body from harm. Many species produce them, but the eye-like marking, and naturally cabochon-like shape of the Turban shell's operculum makes it special. Throughout many centuries, visitors to the South Seas, and sailors returning from there brought home trinkets featuring this exotic gem.

[Victorian Era shell and opercula bracelet: Image courtesy of www.fraleigh.ca, contemporary operculum pendant with back view giving away it's snail origin] Insects as Ornament With the exception of entomologists, few find much of beauty in the insect world. Surprisingly, though, insects have had their part to play in the saga of jewelry history. Once again it is the Victorians who most exploited this resource. The stylized form of the scarab beetle has since earliest historic times been memorialized in faience, metal and gemstone jewelry, yes, but during that period known as the Egyptian Revival, the actual insect itself was a popular jewelry item. After being carefully dried, and possibly coated with a thin layer of lacquer, they were used for brooches, earrings and pendants of surprising durability. Insect wings have also been used, especially those of butterflies and moths in creating "paintings" and jewelry items, these, however, generally had to be encased in glass or plastic in order to be wearable.

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[Egyptian Revival Period natural scarab brooch (and back view), 1930's butterfly wing pendant] Shagreen Shagreen is the tanned hide of sharks and certain rays. It has a long history as an ornamental material from Japanese Shogun era sword hilts, to French Revolution era furniture veneers, to Art Deco jewelry. It is beautiful, relatively durable, and has a unique, bumpy texture that inspires devotion in many collectors.

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[Circa 1900 crystal and sterling shagreen jar with closeup to show texture, 1920's chrome, dyed shagreen cuff bracelet] Beauty is in the eye...... Of the friends and acquaintances who have been invited to view my collection of odd organics, the object below is the one most often singled out as supremely hideous! Personally, I find it has a sort of Charles Bronsonesque loveable ugliness. This early 20th century item is a grouse foot brooch (yes, it is a real foot), and was lovingly made with sterling silver and foilback paste "topaz" gems in Scotland. To each his own, but I always smile picturing some kilt-clad kinsman of mine (my maiden name is Walker) wearing this good luck token during his grouse hunt through the heathered hills.

[Scottish grouse foot brooch] Care and Value Little can be said that applies equally to all the specimens shown here. A biological rule of thumb however, is that if it is an organic molecule, like protein,something eats it. Organic gems containing, or made of, protein (and that is most of them) should be kept dry, and when not being worn or used, protected from exposure to insect, bacterial or fungal invaders. This may mean keeping treasured antique pieces in vacuum sealed bags, or in boxes with "moth crystals". Proteinaceous materials are also sensitive to heat and can be ruined by temperatures that wouldn't begin to phase a mineral gem. The calcareous types such as the conch pearl, are, like their more familiar nacreous cousins, sensitive to heat and chemicals. Additionally most organics should be protected from prolonged exposure to strong light to prevent loss of color which is generally derived from fragile organic pigments. As with virtually all gems, size, color and freedom from flaws set value within a particular type. When dealing in antiques and art objects, the age, quality, and condition are the premier value points.

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From modestly priced and common antler or horn items to stratospherically expensive, vanishingly rare hornbill ivory or melo melo pearls, the world of unusual organics is one that every gem lover and collector, no matter what their budget and tastes, can and should enjoy. Gemological Data: Varies with species

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Zircon The beautiful, historically important gemstone, zircon, has unfortunately, in recent years been tarnished by its name-only similarity to cheap, ubiquitous, synthetic cubic zirconia. The two are totally distinct in their chemistry, optical properties and origins, though. A natural gemstone, which occurs in various colors; zircon is found in many Asian countries, notably Cambodia and Sri Lanka as well as in Brazil, Australia and East Africa. Colorless when pure, zirconium silicate takes on various shades due to impurities. The most common color in the natural rough is yellowish brown. The original diamond simulants, colorless or "white" zircons, if well cut, can be visually convincing, but are easily distinguished from diamond by their double refraction and the tendency to wear along facet edges. Brownish stones are often heated either with or without oxygen to achieve a colorless state or shades of blue, red and golden yellow. The rich, slightly greenish blue heated zircons had at one time been marketed as "starlite", but the term never caught on. Some zircon crystals contain naturally radioactive thorium and uranium. Over time, this radioactivity breaks down the crystal structure so that such stones (always green) tend to an amorphous, glass-like state, with a lower refractive index and luster than the crystalline type. These unenhanced gems are referred to as "metamict" and are sought after collector's items. The high birefringence of zircon makes it necessary for the cutter to orient the table of the stone to the optic axis; otherwise the interior may look fuzzy, due to facet image doubling. Round stones are often given a "zircon" cut which is similar to a standard round brilliant cut with an extra tier of facets at the culet. Although use in rings should be limited to protective settings or occasional wear jewelry, in general, zircon is a magnificent jewelry stone. With a luster just short of diamond and a very high refractive index, exceptional brilliance is possible when a piece is well cut and polished. That stones with light body color may show strong dispersion is a bonus. Collectors appreciate the many color forms but especially seek out reds and greens.

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[Heat treated zircons: golden, blue, white zircon used as a diamond simulant]

[Metamict green zircon, cat'seye zircon],

Value Medium dark, pure blue stones have the highest value, followed closely by those with a saturated greenish blue color. Red stones (always with some orangey hue) in larger sizes also command relatively high prices. Cut is an important factor in value as the vast majority of zircons in the market, especially blues, have been native cut. A custom cut, therefore, enhances value. Sizes of zircon rough is not as limited as in some species, so although there is some premium per carat for larger stones it is not exponential. Cat'seye stones are quite rare in this species and especially valued.

Gemological Data Makeup: ZrSiO4 Luster: subadamantine Hardness: 7.5 Crystal structure: tetragonal Fracture: concoidal Cleavage: none Density: 4.69

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RI: 1.93 - 1.98 Birefringence: .059 Dispersion: .038

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Blue Topaz Blue topaz begins "life" as colorless or very lightly tinted natural topaz crystals which are then irradiated to change the color to blue, and heated to stabilize the change. Neutron bombardment in a nuclear reactor produces the deep slightly greenish or greyish London Blue, while electron bombardment in a linear accelerator results in the light aqua-like blue, known as sky blue. Combinations of both treatments produce the highly saturated Swiss and electric blues. If neutron bombardment has been used, there is residual radioactivity, and the gems must be held, up to a year, before they have "cooled" enough to be worn. The modest value of most blue topaz creates little incentive in the market for a synthetic version, although it is sometimes simulated by blue synthetic spinel. (More lucrative and popular are the various vapor deposition or diffusion coatings that create "mystic topaz" and teal and sea green colors. Such stones are attractive but the treatment is not permanent, with their extremely thin coating they must be handled very gently as any scratch or abrasion can remove the surface layer.) Whatever the color, topaz has some wonderful gem qualities due to its high refractive index and its ability to take a fabulous polish. The fact that the rough is available at moderate prices in rather large, clean pieces means that many cutters and carvers choose this gem for their projects. At hardness 8 topaz makes a good gem for occasional wear rings, pendants, earrings or brooches, but, alas, the ready cleavage of this gem makes its use in daily wear rings very risky.

[The family of irradiated blue topaz: London blue, Swiss blue (with opal), sky blue]

Value In general, blue topaz is modestly priced, although, due to recent shortages, the London blue color has outstripped the others in value. The shortage is 452

due to poor economics: reactor time is expensive and there are more profitable gems which can be treated without the need for such an extensive holding period. There is no special premium for larger stones in this variety and excellent clarity is routinely expected, so included pieces should be extremely inexpensive. Cut often adds as much or more value to the piece than the material itself. Spectacular cuts and carvings are available at generally reasonable prices.

Gemological Data: Makeup: Aluminum fluorohydroxysilicate Luster: Vitreous Hardness: 8 Crystal structure: Orthorhombic Fracture: conchoidal Cleavage: Perfect, one direction Density: 3.54 RI: 1.62 - 1.63 Birefringence: 0.014 Pleochroism: generally weak

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Iolite This gem, which represents one of the few relatively available and affordable blue stone options, is rapidly gaining in popularity. Arguably, the gain is due more to exposure in mail order catalogs and on cable shopping channels than to promotion by traditional jewelry stores. Run of the mill stones often have a steely, inky or washed out blue color, but the best specimens can rival AAA Tanzanite in the saturation of their blue-violet hue at some viewing angles. Iolite is a prime example of a pleochroic gemstone, that is, one whose color depends of the angle of view relative to its crystal axes. As a stone with this property is slowly rotated, a blend of colors appears, then the "true" color for that crytal axis, then another blend, then the other "true" color, etc. The majority of pleochroic stones show two colors, iolite has three. The cutter, then, must orient the rough carefully, taking iolite's trichroism of blueviolet, grey and near colorless into account in order to achieve an attractive "face up" color. Depending on the color of the rough material a stone might be step cut to deepen or enhance color, or windowed and/or shallow cut to lighten the tone.

[Concave cut iolite freeform, round brilliant cut iolites in earrings] So far, no treatments have been successfully used to lighten color or to remove inclusions, so one can, at least at this point, assume that iolite gems are untreated. Its hardness of 7-7.5 makes it a suitable jewelry stone, though the presence of cleavage must be taken into account and some care exercised. Most of the iolite in world commerce comes from India, but substantial amounts are also mined in Tanzania, Brazil and Sri Lanka.

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[Iolite carvings, iolite cabochon]

Value Color is foremost in setting value in this gem, as with most colored gemstones. A saturated, medium dark blue-violet is the ideal for the face up color, but it must be accepted that such stones will always lighten and darken, and show greyish tones as they are turned. Cutting cannot be ignored as poorly oriented, cut and polished stones may have muddy, washed out or inky color. Cabochons are available and reasonably priced. Occasionally, iolite is used as a carving material. Small faceted stones are relatively common and modestly priced. Faceted stones over about 6 carats, that are eyeclean, or better are quite rare and highly valued. Gemological Data Makeup: a magnesium, aluminum silicate Luster: Vitreous Hardness: 7 - 7.5 Crystal structure: Orthorhombic Fracture: conchoidal to uneven Cleavage: distinct, in one direction Density: 2.61 RI: 1.54-1.55 Birefringence: .01 Pleiochroism: blue-violet, grey, light yellow to colorless 455

OREGON SUNSTONE Prior to the finds of substantial amounts of facetable plagioclase feldspar crystals in Oregon, most sunstone, much of which came from India, was opaque and used for cabbing, bead, or carving material. Such is the case no longer. An incredible variety of high value sunstone rough is now being extracted by several mining companies as well as on public collecting sites in Oregon. Although most of the rough is pale yellow in color, a substantial amount of more interesting material is being found. Two main features are notable in high value rough collected from this location: 1) strong body colors ranging from pinks and tans to oranges, greens and reds as well as biand tri-colors, and 2) fine grained coppery shiller which allows for transparency in the stone yet still produces the phenomenon of aventurescence or "glitter". Every combination of shiller or lack of it, and color is found. Collectors and jewelry lovers from all over the world are fast becoming aware of this uniquely American gemstone and appreciate it as one of the shrinking number of materials that can be correctly assumed to be completely untreated and unenhanced. As with other feldspar gems, gentle treatment and protective settings are called for, and use in everyday rings is not advisable. To date there are no synthetics in the market.

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[Oregon sunstones: red, green (slight bi-color), shiller, bi-colored carving, pale yellow fantasy cut stone] Value Because there are so many different kinds of sunstone, the values range widely. The least valuable form is the pale yellow to colorless non-shiller type which in commerical cut, or calibrated stones may go for a few dollars per carat, and for custom cut stones somewhat more. The pinks and tans with and without shiller have additional value, depending on the color and effect. Some greens, strong pinks and reds as well as the bicolored and tricolored stones with and without shiller are much more valuable. The most desirable color is red with large (over 3 carat) stones of prime color retailing at prices rivaling fine sapphires and emeralds. The best greens are very rare and can cost more than the best reds. Oregon sunstone, especially shiller or bi-color pieces are often used for fine art carving material; and the carvings are valued as much for their artistic merit (and the fame of the artist) as for the value of the material itself. Gemological Data Makeup: a calcium rich species of plagioclase feldspar, sometimes with copper or hematite inclusions and traces of iron; 32% Albite, 68% Anorthite 457

Luster: Vitreous Hardness: 6 - 6.5 Cleavage: 2, Perfect Fracture: splintery to uneven Density: 2.70 RI: 1.56 - 1.57

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Spinel Spinel, especially in its red and blue color varieties, is a historically important gem. Because it was often found with corundum in gem deposits and has a similar color range, luster and hardness, it was, until modern times, used unknowingly as sapphire, and especially ruby. The famous "Black Prince's Ruby" which forms part of the Crown Jewels of England, is, in fact, a red spinel. The advent of modern gemological identification and separation techniques in the later 19th century established spinel as a distinct species.

[Prior to the 20th century these spinel gems would have been called ruby and sapphire] In another essay I referred to malachite as the "Rodney Dangerfield" of gemstones, but perhaps that description is even more apt for spinel. Early in the 20th century soon after Auguste Verneuil invented the flame fusion process for making synthetic sapphire, synthetic spinel was made by the same method. For many years, if the public was aware of spinel at all, it was as an imitation found in birthstone jewelry and high school class rings. It's true that the synthetic stuff is as common as dirt, and almost as cheap, but fine natural spinel is, and has always been, a rare gem. Only recently, as the level of gemological awareness of consumers has begun to rise has spinel finally been "getting some respect". This increased appreciation stems not only from the gem's inherent rarity and beauty, but also from the fact that virtually all spinels in today's market are unenhanced. As more information comes to light about the extensive and invasive treatments given to lower grade ruby and sapphire to "pump up" their color or clarity, spinel's natural beauty, and still relatively modest prices, become ever more inviting. Found traditionally in Burma (Myanmar) and Sri Lanka (Ceylon), and more recently from various sites in Vietnam, Africa, Russia, and Australia, spinel is usually mined not from the hard rock primary deposits in which it forms, but from alluvial or placer deposits where eroded material has been washed down stream. These "gem gravels" may consist of several different 459

species in addition to spinel, but have in common that the rolling and tumbling action has smoothed the rough crystals into rounded shapes, and in the process removed much of the included and fractured parts of the gem rough. Such alluvial rough makes good faceting material -- well shaped for recovery and relatively clean. Mining methods range from primitive to low technology (from one or more miners and with their straw baskets sluicing the stream gravel, to the use of backhoes and hydraulic hoses for removing overburden from long buried streambeds, and supplying larger amounts of water for gem separation by a small crew).

[Alluvial spinel pebbles, a joy to facet, "state of the art" alluvial spinel and ruby mine in Vietnam: Image courtesy of www.gemsfromearth.com] When spinel is found at the site of formation (often in metamorphic rock deposits) one of its most beautiful crystal "habits" is that of the octahedron. You may know that diamonds also naturally occur in this form, which is one shown only by gems belonging to the cubic crystal system. In my eyes a blazing red spinel octahedron is one of Nature's most beautiful productions.

[Natural octahedral spinel crystal, spinel crystals in their site of formation: white calcite marble] Spinel is an example of an "allochromatic" gemstone. This means that when the mineral, in this case (MgAl2O4) is pure, it is colorless -- various colors are dervived only from the presence of trace elements acting as 460

chromophores, for spinel these would most commonly be chromium, iron and cobalt. The majority of jewelry gems fall into this category: corundum (sapphire and ruby), topaz, quartz and beryl for example all have colorless varieties which are those formed without the color-making "impurities". For the majority of the allochromatic gems the colorless type is the most common, and therefore the least valuable. Compare for example the value of the finest quality 5 carat emerald (green beryl) with a equivalently fine 5 carat Goshenite (colorless beryl). Those tiny trace amounts of chromium or vanadium that give the emerald its vibrant green bring the price up at least 100 fold compared to the pure beryl mineral. A similiar illustration could be made of ruby vs white sapphire or amethyst vs rock crystal quartz. Spinel is an exception to this pattern. Until quite recently no colorless spinel had been found in Nature. Lab production was easily possible (colorless spinel can be made by the bucketful), but apparently the conditions under which this gem forms in Nature rarely exclude the coloring trace elements, making the colorless natural stone a rare and valuable collector gem! And spinel does, indeed, form in many colors: ranging throughout all shades of pink, lavender, red, red-orange, purple, blue and even black. The only part of the spectrum that seems to be omitted is the pure green and yellow.

[The many colors of spinel: a suite of African spinels in purple, blue and pink, a top red Burmese spinel, an African lavender stone, a pink specimen from Russia , a "padparashah" colored African piece, and an opaque black spinel] Color and Value in Spinel By far the most common colors, and therefore those lowest in value, are pale to medium mauve-pink and greyish light purples. (I have a gardener friend 461

who once described this pink-mauve color as "Garden of Eden" because left to their own devices, most of her fancy colored hybrid flowers would self-sew and grow into "wild types" of precisely this color.) The color (and therefore value) difference between the two spinel ring stones below is mainly that of "saturation". This term doesn't, as is often thought, mean deepness or darkness, but refers instead to absense of grey and brown tones, that is, the spectral purity of a color. In the world of gem pricing, saturation is the main player. You could easily expect to pay 5 to 10 times as much per carat for the true red one on the right as for the less saturated pink one on the left.

[Pink spinel, pretty, but somewhat desaturated and relatively common, spectral red spinel, pretty, close to top-level saturation, and super-rare!] In the purple and blue hues, spinel is most often a relatively steely or greyish color or quite dark in tone, either of which depresses the price. At present, even though popularity is beginning to rise, spinel is still a great gem bargain. I hope this happy situation continues, but quite honestly, my advice is to buy spinel now, before the rest of the gem consuming public really catches on, and prices go through the roof.

[Subtle perhaps, especially on a computer monitor, but the stone on the left is greyer and therefore worth considerably less per carat than the stone in the middle, while those on the right are a shade too dark for top value] Jewelry Use Regardless of color, spinel's high refractive index insures excellent brilliance in a well cut and polished stone, and its hardness of 8 makes it a good choice for almost all jewelry applications -- rings included. I still wouldn't recommend it for a high "Tiffany-type" setting in a engagement or 462

signature ring that will be worn 24/7 for years, but for any less demanding use, it is a wonderful gem. No special cleaning or care instructions apply. The majority of the spinel jewelry for sale today is in the pink and red color range. I expect this to change as the variously colored African spinels make more of an impact on the market. Black spinel, by the way, makes a less expensive substitute for black diamond and a more durable, if more expensive, alternate for black onyx. Spinel beads are relatively rare in the marketplace, but sometimes sold by vendors who specialize in higher grade goods.

[Red spinel in an engraved custom gold mounting, faceted black spinels with Mawsitsit in earrings]

[Red spinel beads, a beautiful, but rarely available choice]

Value in General The most highly valued spinels are the reds with purplish red (ruby spinels) and orangey red (known as flame spinels) colors, commanding the premium prices. Top quality red spinels are actually rarer than top quality rubies, although they are not as expensive. Burmese provenance in fine stones always adds value. As with all stones, values are highest for rich, saturated colors in clean stones and large sizes. Pink spinels in hues from bubblegum color to hot 463

pinks are sought after. The blues and violets, unless the color is highly saturated are, in general, more modestly priced. Among the blue stones, those colored by cobalt are especially valued for their pure, rich color. Star stones and color change varieties are rare in this species and highly valued. Spinels can generally be assumed, at present, to be unenhanced, although gemologists are keeping close watch for new developments along this line.

[Star spinel, a rare collector gem]

Gemological Data: Makeup: Magnesium aluminum oxide Luster: Vitreous Hardness: 8 Crystal structure: Cubic Fracture: Conchoidal Cleavage: None Density: 3.60 RI: 1.71-1.73 Birefringence: None Pleiochroism: None Dispersion: .020

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Uvarovite Garnet Few people, other than gem collectors, are familiar with Uvarovite garnets, and fewer still have seen a transparent faceted gem of this variety. The main reason is that although crystals of reasonable size do occur on occasion in chromite and serpentine deposits, they are generally opaque. Very rarely, a tiny portion of a crystal will have transparency and a small gem can be cut. This type of garnet, therefore, would usually not be included in lists of gem garnets if it weren't for one major source area in the Ural Mts. of Russia that yields lovely Uvarovite drusy. Uvarovite, one of the calcium rich members of the garnet group, is formed through metamorphism of certain silica rich limestones and is often found in association with chromite and serpentine. Those "parent" rocks contain chromium, the source of Uvarovite's rich and distinctive medium dark to dark emerald green color. Finland, South Africa and California provide secondary sources, but little of the material from those locales rivals the beauty of the Russian gems, although some of the Finnish deposits produce large individual or crystal clusters that are cherished by mineral collectors.

[Rough rock from Russia showing a drusy crust of Uvarovite, cabochons showing darker and lighter shades of green] When minerals adopt a drusy crystal habit, tiny to very tiny crystals are deposited on a matrix surface. It is these rather rare occurrences that give rise to the lovely green gemstone, Uvarovite garnet drusy. This gem is unique on two counts --> no such vibrant green color is to be found in the world of undyed drusy materials, and, in addition it is the only species of garnet that is consistently green (idiochromatic). The somewhat intimidating name (pronounced: oo--vare--oh--vite) is in honor of Count S. S, Uvarov, a Russian nobleman once president of the St. Petersburg Academy.

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[An impressively large cabochon, and a 20x magnification of its drusy surface] Although a member of the cubic crystal system, individual Uvarovite crystals can form more rounded shapes, with 12 - 24 rhomboid or trapezoidal faces, in rare cases achieving almost a perfect soccer-ball shape.

[Idealized drawing of a rhombic dodecahedron, a classic Uvarovite crystal habit] Since the rise in popularity of drusy gems with designers in the last decade, Uvarovite itself, and jewelry using it, have occasionally been featured in photos in gem and jewelry publications.

[Designer 14k Uvarovite and Demantoid Garnet Pendant] Garnets, in general, are durable gemstones which can be used for all jewelry purposes, but Uvarovite drusy, as with all drusy materials, should be considered more fragile than a faceted or cabbed gem of its species. Reasonable care is needed in setting and wearing to prevent crushing or 466

dislodging the tiny crystals adhering to the matrix. Ultrasonics and steam cleaners would probably be too harsh, but the old standby of a soft brush, warm water and mild detergent would be fine. Use in pendants, brooches and earrings would be safe, but use in bracelets, belt buckles or rings would be ill advised unless the settings were extremely protective and the pieces infrequently worn. Value Considerations Uvarovite is is too rarely used to have a "standard" price range. Nonetheless, certain guidelines can help the buyer in choosing a good piece of material and getting good value for their money. As with all drusy materials, highest value is accorded to pieces that show even coverage of the matrix by the crystals. With this particular gem whose refractive index is quite high, having crystals which are larger than the powdery form seen in most deposits creates an attractively sparkly surface and are preferred. Like most gems, the brighter the color and more attractive the cut, the higher the value. All else being equal, larger pieces sell for more per carat than the smaller ones as most useable roughs are small. Gemological Properties: Chemical Composition: Calcium Chromium Silicate (Ca3Cr2(Si04)3 Crystal System: Cubic RI: 1.86 - 1.87 Density: 3.77 Fracture: Conchoidal Cleavage: None Florescence: None Luster: Vitreous Hardness: 7.5 Toughness: Fair

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Synthetics, Simulants and Fakes These terms, which are commonly used to describe gems that are not natural gemstones, but which are being sold in place of a natural gemstone, can easily be misused and/or misunderstood. Let's take an example: if I have a natural ruby (one made by Mother Nature's processes) and I represent it as a natural ruby, fine. But under what conditions would I have an example of a synthetic, a simulant and a fake ruby? Gemstones First things first: the word, "gemstone". According to FTC regulations, which guide the gem and jewelry industry's trade and advertising, only natural mineral and organic materials can be legally and ethically sold and advertised as "gemstones". Other terminology, such as "synthetic" or the equivalent terms "cultured", "created" or "laboratory grown" must be used for materials which did not originate in Nature. Synthetics A synthetic has been manufactured in a laboratory or factory. Synthetics may or may not have natural analogs. Synthetic ruby, for example, is a manmade version of natural ruby and is virtually identical to it in both chemical composition and crystal structure. As a result both types show the same physical and optical properties (like density and refractive index).

Cut and "rough" synthetic flame fusion ruby Cubic zirconia and YAG (yttrium aluminum garnet) are examples of synthetics which have no exact natural counterparts and have their own unique chemical compositions and/or crystal structures.

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Yttrium aluminum garnets, YAG, in colorless and green. The first synthetics, produced in a size and at a cost to make them marketable, were synthetic rubies made by August Verneuil around 1900. (Many people don't realize that synthetics go that far back, and have been bitterly disappointed to find that the wonderful Edwardian or Art Nouveau ring they inherited from Great Aunt Minnie was set with a synthetic!) In fact, synthetics were, for a while, with some designers, kind of the "cool new thing" and were not relegated to second tier or mass produced jewelry as they tend to be today.

[1910 14k gold, diamond and synthetic ruby ring: Image courtesy of Acanthus Antiques, Art Deco (circa 1920's) Platinum, diamond, natural pearl necklace, set with synthetic sapphires on the clasp] The process Verneuil developed, called "flame fusion" is still the main one being used to produce synthetic corundum and synthetic spinel. A powdered source material, like aluminum oxide for corundum with, a metallic oxide such as chromium oxide to provide the red color, is melted. As it drops through an oxy-hydrogen torch flame the molten material crystalizes as it hits a ceramic platform at the, cooler, base of the furnace. As the crystal grows the platform is turned and lowered, creating a carrot-shaped "boule".

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Because synthetics have the same optical, chemical and physical properties as the natural materials they mimic, standard gemological tests are not very useful in identifying them. In these cases the microscope becomes a gemologist's most valuable tool in separating the synthetics from gems of natural origin. There are microscopic inclusions which occur only in natural gems, and those which occur only in synthetics. Unfortunately, there are also many inclusions which can occur in either type, and flawless stones with no inclusions to see. The flame fusion materials are usually the easiest type of synthetics to discriminate from their natural counterparts. The most definitive sign is known as "curved striae" which under magnification, in diffused light, look a bit like the grooves on an old vinyl recording.

Curved striae in a flame fusion corundum Triangular platinum crystals (from the crucible) such as seen in a "flux melt" synthetic Alexandrite are another absolute indicator of synthetic status. 470

Platinum crystals in a synthetic gem/ Image courtesy of Martin Fuller, Copyright, 2004 Over the years many new processes have been developed which, although more expensive and time consuming, produce synthetics which have more natural looking colors and inclusions. Some of these, like the hydrothermal process, which is responsible for so much of the synthetic emerald in commerce, mimic the conditions of Nature, others likeVerneuil's are entirely human inventions. Simulants A simulant is any material, natural or synthetic, that looks like, and is used in place of, another material (natural or synthetic), but is not represented to be the natural gem. The term, "imitation" is equivalent to simulant. For example a natural simulant of ruby is the gemstone, red spinel which can have a color and luster very like that of a ruby. On the other hand, red, man-made glass has long been used as an inexpenisve ruby simulant. Simulants have been around since antiquity. As early as 4700 BC, Eqyptians produced a non-clay, ceramic compound, colored by copper, called faience with an appearance very similar to turquoise.

[Egyptian Faience beads circa 300-600 BCE] In the 18th century Joseph Strass, of Vienna, developed a particularly brilliant and dispersive type of lead containing glass, which came to be known as "strass" or flint glass, and which was widely used as a diamond simulant. Today this dispersive type of leaded glass, is generally marketed as

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"crystal" (a misnomer, of course, since all glasses are amorphous, not crystalline). Simulants are less common than they once were as the availability of relatively inexpensive synthetics for many materials have made them less desirable. Some gems that are still commonly simulated, though, include "faux": pearls, turquoise, opal, coral, emerald and of course, diamonds.

Simulated opal (plastic)/ Simulated emerald (spinel triplet)/Simulated diamond (cubic zirconia) Fakes A fake is any gem material, natural or synthetic, which is misrepresented to be any other gem material, natural or synthetic. A synthetic ruby, a natural red spinel, or a piece of red glass would all be fakes if represented as natural rubies. Whether something is a "fake" rather than a synthetic or a simulant is a matter of intention and disclosure. When misrepresentation occurs (whether knowingly or not) then you have a fake. Fakes have been around as long as there have been been dishonest, and greedy sellers and gullible buyers. A rather recent case in point occurred after the Mt. St. Helen's eruption in the US. Materials, purported to be made from the eruption ash, appeared on the market under various names: Helenite, Mt. St. Helen's Emerald, Obsidianite and Mt. St. Helen's Glass. Prices ranged from modest to $100/ct. Subsequent laboratory analysis of these pieces showed that they contained, if anything, a barely measureable trace of ash from the eruption and were quite ordinary man-made green glass.

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"Helenite": a recent case of fakery When "natural" transparent gems are sold in closed mountings so that the crown is the only visible part, your "fake detector" should be on alert. Certainly there are cases when such gems are exactly what they are purported to be, but the vast majority of fakes are set in this way, especially in vintage jewelry.

Foil back glass "gems", the metallic gold coating which increases brilliance is almost completely hidden by the mounting in this circa 1950 brooch. One of the most important roles of GIA (Gemological Institute of America), AGTA (American Gem Trade Association), IGS (International Gem Society) and other gem organizations has been in developing testing procedures and instruments, and in educating honest dealers and intelligent buyers in an ongoing effort to keep one step ahead of those who would deceive.

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Assembled Stones An assembled stone is one that is constructed out of two or more materials. This category includes, for example, such creations as: doublets and triplets, intarsias and inlays, foilbacks and Mabe pearls. There are four common reasons why such pieces are made: #1) To make use of otherwise unsuitable or fragile gem material. #2) To create an entirely new category of gem product. #3) To provide an inexpensive simulant for an expensive natural gem. #4) To deceive a buyer into thinking the piece is something more valuable. Doublets and Triplets Most gem lovers are familiar with doublets and triplets, especially the opal variety. Opal frequently occurs as thin seams of material within a host or matrix rock. Although beautifully colored, such deposits are so thin and fragile as to be useless for jewelry. By cementing one of these thin layers to a strong backing (almost always black onyx or something similar) two goals can be acheived. The strong backing provides the thickness and strength needed for setting, and the dark color makes the usually translucent opal layer look like black or dark grey opal. The color play in the gem material is then displayed in high contrast against this dark background. An opal doublet must still be set and worn with care, as the exposed opal surface is relatively soft. Well done pieces look wonderful, and make affordable, reasonably durable, opal jewelry.

[Opal doublets]

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(Boulder and matrix opals have sometimes been referred to as "natural doublets" although, in my view, this term is an oxymoron. These natural materials are fashioned with their thin opal seams showing on the surface of the natural matrix in which they formed and are not assembled stones.)

[Boulder opals-not assembled stones} Opal triplets have a colorless, usually somewhat domed, cap cemented to the doublet. Such caps are made of scratch resistant, tough materials, like rock crystal quartz, synthetic colorless spinel or even synthetic colorless sapphire. Although such products are quite durable, they lack the natural appearance of well made doublets.

[Opal triplet (inlay)] Since ammolite has gained in popularity and recognition as a gem material, another type of doublet and triplet have become common. Ammolite is the trade name for the fossilized shell of an extinct ammonite mollusc (related to today's Nautilus). The iridescent layer that is so highly valued, is quite thin and extremely fragile and lays over a relatively soft matrix. for this reason, virtually all ammolite gems have been, as a minimum, stabilized with resin impregnated into it, by a proprietary vacuum process. Even these pieces, called "solid ammolites" are quite fragile and must be given highly protective settings or worn infrequently. By making doublets or triplets from ammolite, it becomes a much more durable material, which can be used in many more jewelry applications.

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[Ammolite doublet, Ammolite triplet] Intarsias and Inlays When small, flat pieces of gem material are set within a recess in a stone tablet to create a pattern or picture, the result is called an intarsia. Some of these creations are reminiscent of minature mosaics and are executed with superb precision and skill. If, instead, such pieces are set into channels within metal, the term inlay is used. Intarsias and inlays illustrate both reasons #1 and #2 for making assembled stones, in that they allow use of small or thin pieces which might otherwise be discarded, and they also provide a unique and lovely gem product, not found in nature.

[Intarsias, inlays] Mabe Pearls Another example of a beautiful man-made creation is the Mabe pearl. These constructions are made from a usually hollow, blister "pearl" harvested from the shell of the Mabe, or butterfly shell mollusc. Not technically a pearl, since it is formed from the shell of the animal, rather than within its body, this mother-of-pearl blister is cut from the shell, filled with a special cement and a mother-of-pearl bead, then cemented to a mother-of-pearl back. These 476

products come in a variety of sizes and styles, and with their flat backs are easily settable. Compared to cultured pearls of the same size, Mabes are quite inexpensive.

[Mabe pearl] Rhinestones Since the advent of reasonably priced synthetics, the number and variety of assembled stones produced for reasons #3 & #4 have diminished. Historically, a foilback, called the "Rhinestone" was an important product of this type. Applying a metal foil or metallic paint backing to a gem, allows it to simulate a much more brilliant material. Rock crystal quartz stones from the Rhine Valley were the first widely used product to receive this treatment, and were once a common choice as diamond simulants. Later the quartz was replaced by glass, but the name stuck. One of my most cherished mementos from my mother is her circa 1940 Rhinestone necklace and earring set. Cubic zirconia is presently the most common diamond simulant on the market, but to my mind lacks the charm of those Rhinestones. Assembled Birthstones Even though synthetic emerald is widely available, as synthetics go, it is quite expensive. This creates a need for a good looking, less expensive substitute. As it turns out, the inexpensive flame fusion process which is used to make synthetic corundum and synthetic spinel in a great variety of colors, cannot yet create a convincing emerald green color. That job is most often filled, at present, by the synthetic spinel triplet. This creation is sold by the thousands, if not millions, as the imitiation May birthstone and in high school and college class rings. This clever, and actually, pretty decent looking, assemblage, consists of a colorless synthetic spinel crown cemeted to a colorless synthetic spinel pavilion with a central layer of green glue or green glass. 477

Fakes and Frauds Although assembled stones had their heydey as deliberate fakes in earlier times, before cheap synthetics made them all but obsolete, there are still some around today to watch out for--> especially if you are purchasing antique jewelry. The most famous example is the garnet and glass doublet. This piece of trickery, if done well, is extremely convincing (I can attest to this personally, as I mis-identified one early in my GIA coursework). The pavilion, and most of the crown of one of these pieces is glass, which can be of almost any color. Red for ruby, blue for sapphire, green for emerald, etc. A thin slice of natural garnet (usually red) is fused by heat and pressure (or sometimes, less convincingly, glued) to the center area of the crown. Then the assemblage is faceted. Although it sounds like you should be able to pick these out a mile away, well done pieces show no red color, face up, and no eye-visible demarkation between the glass and the garnet. The garnet provides durability, high luster and brilliance and even some natural looking inclusions when magnified. Once placed in a setting they are excellent forgeries and would pass all but the most thorough examinations. A doublet, foilback, or any other assembled stone, can be a fake if it is misrepresented as a natural or solid gem, and when set in a closed bezel may look completely convincing. Unset gems are much more difficult to pass off as something they aren't. To illustrate, if you look at a solid opal from the side, it is obvious that you are seeing a single, uniform material. Look at an opal doublet from the side, and you'll see a sharp demarcation in a straight line between the opal and the base. (Natural boulder or matrix opals when viewed this way have irregularities and undulations between their opal layer and the matrix which makes them easy to distinguish from either a solid piece or a doublet.) Triplets are the easiest of all to identify, even when set, as their colorless crown is obvious from just about any angle. It would take many pages to catalog the multitude of assembled fakes that have been, and are still, occasionally, being used. There certainly has been no shortage of human ingenuity in this department. Deceivers will try just about anything, and sad to say, they still, sometimes, find willing buyers. Reputable dealers fully disclose the nature of the materials they sell. The current AGTA standards for labeling assembled gems for sale, specify the following gem ehancement code: [Gec: ASBL]. Care

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The care and wearing recommendations for assembled stones, vary with the materials involved and method of assembly, but certainly ultrasonic and steam cleaning should be avoided. It would also be prudent to have such stones removed, when jewelry containing them is repaired or sized. In general, erring on the side of caution would be a good idea. Overall For the most part, even though they have been used to deceive, assembled stones have brought increased variety, beauty, practicality and affordability to the gem marketplace. **********

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Natural Pearls Prior to the 19th century, when they were superseded in price by diamonds, natural pearls had, throughout history, been valued above all other gems. Although their beauty, and the fact that they come out of the mollusk ready to use, were important factors, it was sheer rarity that drove their value to the highest levels. The formation of a large, beautiful and perfect natural pearl is an event so unlikely in Nature that only those at the pinnacle of wealth and power in a society were able to own them. Depending on the species between 1/1000 to 1/500,000 mollusks will form pearls during their lifespan, and the vast majority of those formed will be small, off-color or flawed. Nacreous Pearls True pearls are referred to as "nacreous pearls" due to their composition. Such a pearl is formed when a small foreign object makes its way into the soft body of a filter-feeding or grazing mollusk, and cannot be expelled. The irritant is sometimes a stray bit of shell or bone, but more often a parasite. Layers of calcium carbonate crystals and protein are secreted to slowly cover all parts of the object which, then, becomes a pearl. If it grows entirely within the body of the animal it will be three-dimensional "cyst pearl", if it grows attached to the shell, it will be a "blister pearl". We can perhaps imagine the awe and mystery that these objects held for the early peoples who found and cherished them, and it is no wonder that mythic and mystical explanations for their formation abounded. Picture harvesting the creature shown below (not all pristine and clean, as shown), but covered with mud and sea weed and inside its greyish, lumpy and slimy interior, finding the iridescent object in the adjacent photo.

[Abalone shell, abalone pearl jewelry: Images courtesy of www.allnaturalpearls.com] The beauty of a nacreous pearl comes from a combination of its shape, color, and surface reflection (luster). In the best specimens these features are 480

heightened by a surface iridescence called "orient". The shape of a pearl will largely be determined by chance (the shape of the irritant), and its anatomical placement in the animal. The body color will vary with the species of mollusk, which will generally make pearls in shades similar to that of their shell lining. The iridescence and/or luster of a pearl will be a consequence of the perfection and thickness of the nacre layers, of which the onion-like pearl is made. Nacre (NAY-ker) is made up of plate-like hexagonal crystals of translucent aragonite (a form of calcium carbonate), conchiolin protien (konk-KY-ohlin) and water. Each crystal is very thin and they are layed down rather like bricks in staggered courses with the proteinaceous "motar" between. Light, reflecting and diffracting from the uneven surface, and the thin inner layers creates the lovely effects of luster and orient.

[Magnified surface of a pearl with its overlapping layers of nacre: Image courtesy of Joe Mirsky] Pearls are made by both salt and freshwater bivalve (two shell: oysters and mussels) and univalve (one shell: snail-like) mollusks. What we call saltwater pearl "oysters", are not closely related to the edible varieties of oyster. So, that plate of oysters you might enjoy for lunch, must remain a gastronomic delight alone, as no pearl will be found in it. If you are a freshwater mussel or saltwater abalone fan, however, your chance of finding a pearl, though slim, exists, as long as you eat them raw (cooking destroys pearls). What's in a name? In today's world, the word "pearl" means "cultured pearl" to almost everyone. Technically, it's illegal to sell or advertise cultured pearls, as pearls, without using the adjective "cultured", but no one really gets very excited about enforcing it. In the present day, natural pearls, due to overfishing and pollution, are even rarer than they were in historical times. Their admirers are not so much the wealthiest among us, as those who for philosophical, spiritual/religious, or aesthetic reasons seek out these rarities. This shift in the position of natural pearls from status symbol to quasi-cult objects, has been the result of the spectacular success of pearl culturing. With its technical beginnings around 1890 and large scale production in 481

force by the early 1920's pearl culturing has made this gem one that is obtainable by virtually anyone in a variety of qualities and prices. How the pearl marketplace has changed, then:

[Circa 1890 2-3.5 mm, natural, saltwater pearl brooch, circa 1920 2.5 - 4 mm, natural saltwater 16" pearl necklace] Natural Pearls: Expensive then, expensive now! And now:

[Circa 1960 4 mm, cultured saltwater pearl brooch (fairly expensive when new), 2005, 18" 7.5 mm, freshwater cultured pearl necklace (very inexpensive)] Cultured Pearls: Size is increasing and prices are dropping! In looking at the photos above we can begin to see why cultured pearls have taken over the world. Natural pearls are generally small, and vary in shape and color, cultured pearls, especially in today's market, are uniform in size, shape, and color and can be huge! It might take an oyster in Nature six or seven years to make a 4 mm pearl, and only 1-2 out of a hundred of them would be round. Furthermore, colors are not uniform. In today's market natural pearls are available through current small scale (legal) harvesting, and also as vintage and antique specimens or jewelry. Examples of natural, nacreous pearls:

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[A contemporary suite of saltwater pearls from the "Rainbow-lipped" oyster: Image courtesy of www.allnaturalpearls.com, Victorian Era seedpearl bride's necklace, Art Deco Era saltwater pearl necklace, contemporary suite of abalone pearls: Image courtesy of www.allnaturalpearls.com, circa 1905 gentleman's saltwater pearl stickpin] Are they really natural? If you're in the market for antique jewelry with natural pearls you need to be aware that imitation pearls have a long history and were sometimes used in surprisingly "upscale" jewelry pieces. The "tooth-test" is generally helpful (although not sanitary). The surface of a nacreous pearl (natural or cultured) will be slightly gritty. This microscopic roughness can be detected by rubbing the pearl, gently, across the edges of your front teeth. Pearl simulants (usually made of glass or shell) have smooth surfaces and don't feel rough. Also if the pearls in your antique piece are uniform in size, luster and color your "fraud antennae" should be on full alert. Non-nacreous "pearls" Technically, the product of a mollusk that is not made of nacre is not a pearl, but a "calcareous concretion". Having said that, I'll point out that they run the gamut from chalky marble like products such as found in edible oysters with no gem value, to some of the most highly valued and rare gems in the world. For the purposes of this essay, I will call these beautiful and valuable ones, "pearls". There are three of note: Conch pearls (pronounced "konk"), scallop pearls, and melo melo pearls. Each of these is made of calcium carbonate but primarily in the form of calcite rather than aragonite, and with different structural characteristics and protein proportions than their nacreous cousins. 483

Conch pearls are products of a large marine snail, the queen conch, It is native to the Caribbean and, until it was fished to near extinction, was found abundantly in the waters of the Florida Keys. Ranging in color from white to vibrant pink, the pearls are usually small (8 mm is large) and ovoid. you can see in the picture below and to the right, the highly desirable "flame structure" chatoyance that the best specimens have. (Conch pearl lovers are not to blame for the decimation of the Florida population, as they are basically just a rare by-product of the hunt for this mollusk: the meat of the conch is a delicacy, its pink shell lining is used in jewelry, especially cameos and the shell itself is a tourist object.)

[Strombus gigas, the Queen conch, with typical pearls: Image courtesy of www.sunlion.com, three top quality conch pearls showing "flame structure": Image courtesy of Aires Jewelers] Scallop pearls The newest type of natural pearl available to collectors is the scallop pearl. It is found in a marine bivalve scallop that is native to the coast of Baja California, and is just beginning to be harvested. Highly variable in size and shape, they have mosaic-like patterns and cream to salmon or mauve colors with a semi-metallic to chatoyant sheen.

[Scallop pearls: Images courtesy of www.allnaturalpearls.com] Melo melo pearls: By far, the hardest to obtain pearls on Earth are those of the marine "baler" snail, found in the Indo-Pacific region: round, smooth and sometimes quite 484

large, I recently held one in my hand that was the size of a large gumball and nearly dropped it when the price of $50,000 was quoted to me. The colors and flame structure are similar to those of the conch pearl.

[Melo melo pearl showing ideal color: Image courtesy of the Latendresse family, Large 30 mm, 150 ct. Melo melo pearl: Image courtesy of Gemopolitan.Ltd] To this date, none of the non-nacreous pearls have been successfully cultured, and each has a unique structure which makes its difficult to fake, so that there is little worry about synthetics and simulants. Value It is difficut to talk, except in generalities, about value for gemstones as rare and variable as natural pearls. The nacreous ones increase exponentially in value with size but luster, color and shape are important as well. With the non-nacreous pearls, color and quality of the any surface pattern or chatoyance are probably more important than size. Care All pearls need gentle care. They are soft, fragile, and are sensitive to chemicals, especially acids. All the cleaning they ever need, is wiping with a damp cloth after each wearing, and they should be stored away from other gems, preferably in a cloth bag or their own case. Non-nacreous pearls should not be exposed to bright light for extended periods as the organic pigments which give them their colors can fade. Pearl strands that are worn frequently should be restrung every few years.

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Freshwater Cultured Pearls (FWCP) Pearls in General Pearl is unique among gemstones, being the only one found within a living creature, and the only one which requires no fashioning (cutting or polishing) before use. Another distinctive feature is its near exclusive use by one gender. Although some efforts have been made to market pearl jewelry to males in recent years, pearls remain the most "feminine" of all gemstones. Designated officially as the June birthstone, they are, unoffically, a near requirement for brides. Cultured Pearls Cultured pearls are those which form in certain mollusks (oysters and mussels) at the intervention of man. Both fresh and saltwater species are used. A shell bead and/or a piece of mantle tissue from another individual is inserted into the interior of the animal. This operation must be done skillfully so that the creature not only survives but accepts the "nucleus". If successful, this process induces the animal to form a "pearl sac" whose cells secrete a layer of brownish protein called conchiolin, (kon-KY-o-lin) over the irritant. This is followed by the secretion of numerous mineral layers of nacre (nay-ker) composed of calcium carbonate (aragonite and/or calcite) in thin overlapping plates.

[Bead nucleation process: Image courtesy of Dr. Jill Banfield] The composition and structure of this nacre is essentially identical to that which forms under natural conditions. The thin layers create a kind of 486

diffraction grating through which light must pass. This diffraction phenomenon is responsible for the surface pearly luster, and if the layers are sufficiently thick and properly aligned, may result in that most prized of all pearl characteristics, an iridesence, called "orient". High quality pearly luster can be described as a satiny shine or glow that goes deeper than the surface. Orient, when present, is unmistakable and breathtaking: a shifting surface layer of spectral colors from subtle to dramatic, depending on the type and quality of the pearl.

[Magnified view of overlapping nacreous plates. Image courtesy of Joe Mirsky] FWCP The culturing process in freshwater pearls takes place over a period of from six months to three or more years, depending on the conditions, the species, and the desired outcome. The mollusks that produce freshwater pearls (both natural and cultured) are mussels that live in rivers and streams. Unlike what is standard procedure for saltwater culturing of pearls, beads are rarely used as a nuclei. Instead, the vast majority of FWCP are "tissue nucleated" only. This means that only mantle tissue is used, and that most of the resulting pearl is composed of nacre, rather than only the outer skin, as in the case of bead nucleation. The various species of fresh water mussels are capable of producing a wider range of natural colors than most saltwater mollusks: from white, cream, yellow, gold, silver, blue and brown to grey. They also grow faster and will tolerate multiple tissue nucleations, so that a harvest of 30-40 pearls from a single animal in 2 years is not uncommon. The slower growing bead nucleated, saltwater types will generally yield only 1 or 2 pearls per animal. It's easy to see why the freshwater types are so much less expensive. Primary sources of production of freshwater cultured pearls are China, Japan, and the US. The process of commercial production of freshwater pearls originated in Japan at the end of the 1920's at Lake Biwa, but various problems such as pollution and viral diseases have hampered production in 487

recent years. Progress is being made in restoring the ecosystems and breeding resistant mollusks, so we may well see the return of Japanese pearls to a prominent place in the market in the future, especially as a result of recent production at Lake Kasumiga of a lovely pink pearl. At present, however, the premier source is China. Chinese FWCP Although once thought of as an inferior product, advances in technique and marketing practices have made today's Chinese freshwater pearl a true gem. Up until the 70's most of the Chinese pearls were small, wrinkled and flat. This earned them the unflattering, but rather descriptive nickname of "rice krispies". These pearls, though not what the public was used to in shape, had to be admired for the depth of luster that being nearly all nacre imparts. Orient, seen only in the finer grades of natural and saltwater cultured pearls was relatively common in these little beauties.

["Rice Krispie" strand and closeup] Inexpensive and available in fun and fantastic shapes, these pearls began to command a larger and larger share of the cultured pearl market that was once dominated by saltwater Akoya pearls.

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[Variety in color and shape in FWCP, note the visible orient in the baroque shapes] As tissue nucleation techniques were improved, larger and more uniform pearls resulted, and symmetry improved so that pear, oval and egg shapes became available. Today some types are very close to round and getting larger, so that their appearance is rivaling their far more costly saltwater cousins.

[Symmetrical oval FWCP, Near round 7.5 mm FWCP, note depth of luster] A small scale new development in Chinese pearl production is the use of bead nucleation. For the present, this is mostly done under wraps and hushhush, but there is strong evidence that some of the largest, and roundest of the pearls have been nucleated with either shell beads, as in saltwater pearl production, or with a nucleus made from another FWCP. If you think about this for a second, though: what better material to use? The resulting pearl is large, very round, and almost pure nacre. I for one, would not be averse to owning such a pearl (as long as it's nature was properly disclosed and I paid an appropriate price for it). 489

American FWCP The rivers of the East Central US, especially the Tennessee River, have long held a special place in pearl culturing. The shell beads used in such quantity in saltwater production come from the mussels living in these rivers. Although many other species' shells, and indeed, many other materials have been tried, these are still the standard. The US commands a substantial and growing share of the market with the FWCP produced from these waters, especially, again, the Tennessee River. Unlike the Japanese and Chinese FWCP, the American ones are bead nucleated. The producers take special care and allow the nacre layers to grow for up to five years, producing a superior pearl. They specialize in fancy and fanciful shapes such as sticks, crosses and wildly shaped baroques. Jewelry designers love the artistic possibilities presented by the unique shapes, and pearl connoisseurs love the depth of nacre, especially in the nooks and crannies of the baroques where it pools and creates intense orient. Added to this is the fact that of all the world's cultured pearls, the American FWCP is the only type that is routinely unenhanced, so you can understand why they have a devoted following even with their somewhat higher prices.

[American FWCP] Economics Culturing pearls is a delicate process, not assured of success. Only 25 - 30% of the altered mollusks survive and produce pearls and generally only a small percentage of the pearls harvested are of fine quality. Several factors determine what a particular pearl farmer will do: the longer the pearl grows, the thicker the nacre and the more durable and potentially beautiful it will be, but at the same time, longer cultivation increases the death rate of the animals and the percentage of damaged and misshapen pearls. Different 490

strategies produce pearls of different overall qualities, aimed at different segments of the market. Because the market for inexpensive pearl jewelry is so vast, most producers aim for crops of plentiful medium to lower grade pearls with just a small percentage of them specializing in fewer, higher quality pearls. Enhancements Enhancements are so common that unless it is specifically stated by the seller, you should assume a FWCP has been at least bleached to remove dark spots of conchiolin which show through the nacre. Most have also been tumble polished to improve surface shine and remove bumps. More dramatic techniques such as dyeing or irradiation produce pearls with exotic colors such as green, black, bright gold and purple.

[Dyed Pearls] Imitations Faux pearls have been around for a long time and can consist of a variety of materials such as glass, plastic or shell with various surface treatments meant to simulate the pearl's luster. The time honored standard material is a lacquer containing an ingredient from ground fish scales called "pearl essence" or "essence d'orient". With FWCP prices at historic lows, there is little incentive to buy or wear imitations. A rule of thumb when testing a suspect pearl, is to rub it across the surface of your teeth. Pearls with a nacre surface (natural or cultured) will feel slightly gritty, most imitations will feel smooth.

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[Glass "pearl" with visible scratches in coating/ plastic "pearl" showing mold mark] Care Although pearls are delicate, they have been successfully used in jewelry for thousands of years. As they are sensitive to heat, chemicals and abrasion, they should be stored in a cloth bag or their own box away from contact with other materials. They should be protected from chemicals such as hairspray and perfume and chlorinated water. Wiping them with a damp cloth after wearing, and occasional cleaning in mild soapy water is all that's required. Under no circumstances should they be placed in an ultrasonic or steam cleaner. Jewelry settings in rings and bracelets should be protective, or if not (as in many pearl rings) the piece should be considered for occasional use only, rather than daily wear. Value FWCP are a bargain. This is especially true as the quality rises, they are far less expensive than similarly sized saltwater pearls and have their own distinctive beauty. The value of any pearl is most related to the thickness and quality of the nacre. A pearl with thin nacre cannot be deeply lustrous or have orient, but not all thick nacred pearls will exhibit those traits either. The thinness, translucency and alignment of the nacre platelets determine its quality. Those with deep luster and visible orient are most desirable. Other factors include size (especially in rounds), shape, and color. In general the highest prices will be paid for large, round, well colored, unenhanced gems. Factors which influence value in pearl jewelry pieces would add to these general considerations, quality of stringing and degree of matching in size and color.

Gemological Properties: Makeup: Calcium carbonate, conchiolin and water Hardness: 3 Toughness: Good Crystal System: Orthorhombic Luster: Pearly 492

Density: 2.71 RI: 1.53 -1.68 Cleavage: None Optical Phenomenon: Orient, in fine specimens

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Saltwater Cultured Pearls (SWCP) Although both natural saltwater and freshwater pearls have all been highly coveted, rare, and valuable gems throughout human history, saltwater pearls were the first to be successfully cultured by man. These creations of the cooperation between man and mollusk increasingly dominated the world pearl market from the early 1930's until about 20 years ago when they were challenged, and then superseded, by freshwater cultured pearls. By the 1950's SWCP were the market, with natural pearls sought only by the rare gem collector, and antique jewelry fan. As I have written previous essays on both natural pearls and freshwater cultured pearls, I will focus my attention in this piece on pearls grown commercially in marine oysters of various species. Farming and Culturing Pearls A number of individuals were important in developing and perfecting the pearl culturing process used today for SWCP, but to be fair, the lion's share of the credit must be given to Kokichi Mikimoto. He was tireless, not only in research and development, but more importantly in marketing, and creating acceptance for the finished product. Without his zeal and persistence in championing the term "cultured", it almost inevitable that "synthetic" or "man-made" would be the adjective used today to describe these gems. Technically, as well, the basics of all the saltwater pearl culturing operations of today, regardless of the type of oyster, or the geographic location, are the same as are those pioneered by Mr. Mikimoto. 1) Oysters, either collected from the wild, or more commonly today, bred in controlled facilities, are opened in a labratory-like facility, and "nucleated" with a shell bead (and a piece of oyster mantle tissue). Highly skilled "surgeons" perform the insertion of the bead into the gonad of the animal, taking care to promote survival by minimizing internal damage. Unlike freshwater mollusks, which accept dozens of nucleations, most saltwater species can accept but one or two. This is partially responsible for the price differential.

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[A "surgeon" nucleating an Akoya oyster: Image courtesy of www.pearlguide.com] 2) The oysters are returned to the sea protected within special rafts or cages to underwater "pearl farms" to grow and produce the nacre layers which cover the bead, and create the pearl. The time necessary varies from six months to several years depending on the size of the bead, the species of oyster, the temperature and other environmental conditions of the water, and the quality of the pearl being sought. Nacre is composed of mineral crystals layered between a protein secretion known as conchiolin.

[Above water views of Akoya and Tahitian pearl farms: Images courtesy of www.pearl-guide.com] Mortality from the nucleation process, and from subsequent disease, water pollution, and weather disasters makes the success rate relatively low, especially in comparison to freshwater culturing where conditions can be more closely controlled. 3) The pearls are harvested, cleaned, sorted and graded by size, quality and color. Color depends on the species of oyster, size is controlled by the size of the bead the animal can accept, and quality is primarily related to the 495

thickness and structural characteristics of the nacre layer. In general, longer in the ocean = thicker nacre, cooler water conditions = more uniform crystals. Depending on the producer and the type of pearl, various enhancements such as bleaching, polishing or dyeing may follow. Three Main Types SWCP differ in size, color and geographic location where they can be grown, mainly due to species differences between the several different oysters that are farmed. (Depending on whether the writer is a "lumper" or a "splitter" when it comes to categorizing things, the number of types differ from four or five to as few as two. Most commonly, the whole group is often divided into three categories: Akoyas, Tahitians and South Seas pearls, so I will stick with that nomenclature.)

[Akoya, Tahitian and South Sea Pearl rings] Pearl Oysters With one exception, the various oysters which produce all types of SWCP are species belonging to the genus Pinctada. For example: Pinctada imbricata, P. margarifera, and P. maxima. (For those not fluent in biological taxonomy this means they are about as related to each other, and as different in their ecological niche, size and outward appearance as are Felis leo, F. domesticus and F. concolor (all cats: lion, house cat, cougar). Rather than use the cumbersome scientific names, though, I'll use the common names which have the additional advantage of giving us hints about the color, geographic range and/or size of the pearls we can expect. They are, in order: the Japanese or "Akoya" oyster, the black lipped oyster, and the silver/gold lipped oyster. The term "lip" refers to the inner rim of the shell that is most characteristic of the mother of pearl color, and therefore most likely to be that of the cultured pearl. (A member of one other genus is just beginning to be cultured in the Sea of Cortez, Pteria sterna, commonly called the rainbow lipped oyster. None of the pearl oysters, by the way, are 496

closely related to the edible oyster, so enjoy those for their taste or nutritional value, but don't expect the bonus of a "pearl" reward. Akoya Pearls The Japanese pearl oyster, native to the cool to temperate seas surrounding Japan, with which Mikimoto began today's multibillion dollar industry, is also known as the "Akoya" oyster, and all pearls produced from this species, whether in Japan or elsewhere, are called Akoya pearls. The animal is small in size, grows slowly, and has a little gonad which will accept only a small bead nucleus. The upper size limit of Akoyas is about 8 mm, and most are smaller. Their natural color range is white, cream, and very subtle pastel shades of silver, tan and pink. Although the nacre layer is generally relatively thin, ( .5 mm - .8 mm) the highly uniform mineral crystals which form in the cool waters give this pearl exquisite luster. Orient, that shifting iridescence sometimes seen on the surface of pearls is usually subtle if present at all. Due to the wide variation in finished size, luster and color, matched strands of high quality Akoyas can be very expensive, especially in larger sizes. The Mikimoto Company continues to retain its reputation for quality (and its top level prices), but many other companies offer Akoyas in a range of qualities and prices.

[This 18 inch, 8 mm strand of Mikimoto brand pearls would retail for well over $3000, Lesser quality, 16 inch non-Mikimoto Akoya strand with pearls grading from 6 mm to 3 mm would be considerably less expensive] The motivation to enhance Akoyas is great, as most have uneven color or dark nucleus spots that can be eliminated by bleaching or slight surface imperfections that can be made less noticeable by polishing. Many Akoya producers use at least these minimal treatments, and some use dyes or irradiation to change color. Those who wish to purchase unenhanced, or minimally enhanced, Akoyas are going to pay a premium for the enormous grading effort and time it takes to produce carefully matched strands. "It's deja vu all over again" 497

At least two decades ago, the freshwater cultured pearl industry which began in Japan at Lake Biwa, and due to pollution, disease, over harvesting, and other problems lost the biggest share of the market to "newcomers" from China. The same nightmare is again playing itself out for Japanese Akoya pearl growers. High labor costs, bad weather, pollution and disease have made the Japanese Akoya noticeably higher priced than the newer crops produced in Chinese waters. Initially the quality difference helped maintain Japanese dominance, but as the Chinese product improved in quality, the inevitable happened. Today the majority of Akoyas sold come from China, and within single strands from even top level brands contain pearls produced from both Japanese and Chinese waters. Tahitian Pearls The products of the black lipped oyster, which grows in a wide area of ocean in the Pacific including French Polynesia and Micronesia, are generally larger than Akoyas (10 mm is common), and range in color from very dark grey to lighter grey and silver, although they are often generically referred to a "black pearls". Their body colors can show overtones of green, pink, lavender, bronze or olive, and they commonly show a strong iridescent display of orient. The reason for their larger size is due to the fact the the oyster itself is larger, and has a bigger gonad which will accept a larger shell bead than the Akoya. The warm, clean waters, help the oysters to grow relatively quickly and be harvested with a relatively high success rate. The nacre layer is generally a lot thicker than in the Akoya, and recent vigilant efforts of the Tahitian pearl industry to enforce growing time and grading standards has reversed the inevitable drive to produce large quantities of thin layered pearls. Many Tahitians are baroque in shape (as seen below), and can be relatively inexpensive but rounds, especially large ones in matched strands are extremely expensive.

[Baroque Tahitian pearls, showing some of their color range] South Sea Pearls

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There are two subspecies or varieties of the South Sea pearl oyster: the silver lipped and the gold lipped. It is the largest in size of all the pearl oysters and produces pearls of 13 mm on average, some much larger. The range is from the waters North of Australia to those South of China, including Indonesia. The site of the richest yellow/gold pearls centers around Indonesia so these are often referred to as "Indonesian" golden pearls. Clean water with rich supplies of plankton encourages fast growth: after 2 years, 2 - 6 mm of nacre may be deposited. Orient is not usually a strong feature, but the warm colors and satiny luster give these large beauties a special appeal. The color range is wide, including creamy white, tan, grey, yellow and gold. Rare colors like a green/gold sometimes called "pistachio" bring a premium.

[Natural color South Sea pearls: golden pearl in custom 18k gold and iolite necklace, "small" 11 mm, yellow gold round, "pistachio" pearl on custom tektite stickpin] Detecting Enhancements in Pearls As with Akoyas, both Tahitian and South Sea pearls can be enhanced by dye or with an irradiation process which darkens the shell nucleus, although such treatments not yet the norm, as are bleaching and light polishing. Dyed or irradiated pearls can sometimes be detected by observing the pearl, and especially the drill hole, at high magnification. Dyes, which affect only the nacre layer, might be seen as concentrations of color near the drill hole or in surface imperfections. Irradiation darkens the inner shell nucleus, not the nacre, so in this case an abrupt difference in color between the nacre and the bead seen at the drill hole will be definitive. A natural colored strand of Tahitians or South Sea pearls can be expected to show slight color variations from pearl to pearl, whereas a strand of dyed pearls will be quite uniform. This observation is less likely to be helpful with Akoyas, where bleaching is more commonly used as an aid to color matching. 499

Blister Pearls, and Mabes Cultured blister pearls are formed when a nucleus is attached to the oyster's (or abalone) shell rather than implanted in the gonad. These have a long history, and were actually produced as curiosities long before the days of Mikimoto. When a blister pearl is removed from the shell, the bead extracted, and the cavity filled with an epoxy resin, then given a flat shell backing, the result is called a Mabe pearl. Technically termed an "assembled cultured pearl product", they are lustrous, can be formed in interesting shapes, and give the buyer a lot of pearl and nacre "bang for the buck".

[American abalone blister pearl carving, Mabe pearl earrings] Imitation Pearls Faux pearls go back hundreds of years, and can be as cheap and obvious as molded plastic, or carefully made and nearly as expensive as freshwater cultured pearls. The premier brand of imitation pearls, Majorcas, with a heritage of cottage industry manufacture going back to the 19th century, still have a loyal following today. Short of examining the pearl surface at 50X magnification to detect the overlapping layers of nacreous plates, the old standby test is to gently run the pearl over the edge of your bottom teeth. A slight, but noticeable gritty texture, indicates a cultured pearl, a smooth texture, an imitation.

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[Gumball machine quality plastic "pearl": note mold mark, 24 inch strand of 7mm Majorca brand "pearls", as facsimiles go, top notch!, magnified view of natural or cultured pearl surface with overlapping layers of nacreous plates: Image courtesy of Joe Mirsky] Care It is true that pearls are delicate, but they are tougher than their statistics might indicate. Hardness of 3 and sensitivity to heat and chemicals on the downside, is partially compensated for by surprisingly good toughness. A pearl's ability to resist chipping and breaking is due to the "bricks and mortar" nature of the nacreous coating. So, with a saltwater cultured pearl, nacre thickness is the key not only to beauty, but also to durability. Inexpensive pearls (especially Akoyas), may have extremely thin nacre layers (less than .5 mm), due to very short growth times. Although these bargain pearls may look pretty good when new, they will rapidly degrade as the fragile nacre layer chips or flakes off, and the dull bead underneath is revealed. Large size in pearls is a tempting quality, but given the same amount of money to spend, a smaller pearl with a thicker nacre layer will be the better investment in lasting beauty. Pearls should be wiped with a damp cloth after wearing, and rare cleaning in mild soapy water is all that's required. Under no circumstances should they be placed in an ultrasonic or steam cleaner. Pearls should be given their own, cloth lined compartments in a jewelry case, not thrown in a jumble with diamond and colored gemstone jewelry. Jewelry settings in rings and bracelets should be protective, or if not (as in many pearl rings) the piece should be considered for occasional use only, rather than daily wear. Pearl strands of substantial monetary or sentimental value, if worn frequently, should be restrung every year or two. This caution is not primarily due to the string weakening and being likely to break. Rather the worry is that as pearls loosen on the strand due to stretching of

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the string (which is inevitable with wear), the knots become free twist and to abrade the nacre/bead junction, and damage the pearl. Value I am speculating, but I think it's pretty safe to say that although many more freshwater than saltwater cultured pearls are sold, the dollar value of the latter far exceeds the former. From the earliest days of pearl culturing at the turn of the 20th century, into the 60's when cultured freshwater pearls first began to enter the market, and still, today, saltwater pearls have been considered to be finer in quality, and are the most expensive type. So many factors go into the valuation of saltwater cultured pearls that it is difficult to make any generalizations. Suffice it to say that the more lustrous, beautifully colored, large and if in strands, the more well matched pearls are, no matter what the species of oyster that produced them, the more they will cost. Rare colors, thick nacre, iridescent orient, lack of enhancements, and exceptional size will bring premium prices.

Gemological Properties: Makeup: Calcium carbonate (aragonite), conchiolin and water Hardness: 3 Toughness: Good Crystal System: Orthorhombic Luster: Pearly Density: 2.71 RI: 1.53 -1.68 Cleavage: None Optical Phenomenon: Orient, in fine specimens

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Sugilite Named for Professor Ken-ichi Sugi, who discovered the mineral in a nongem form in Japan in 1944, the first gem grade, commercially exploitable deposits were not found until 1979 in the Wessels' Mine area of the South African Kuruman manganese fields. Although pure Sugilite, a complex silicate which gets its purple color from manganese, is a mineral species, much of the more variously colored material commonly cut into cabochons, and called Sugilite is technically a rock composed of both Sugilite and chalcedony. Sugilite was formed in deep beds of manganese-containing metamorpic rocks that were later invaded by silica rich hydrothermal fluids.

[Rough sugilite from S. Africa] Sugilite occurs as a microcrystalline aggregate and ranges in color from dark to medium purple, with variable amounts of dark or light mottling when chalcedony is present. Although a small percentage of the rough is translucent, most pieces seen on the market are opaque. The pure purple specimens which are nearly 100% Sugilite are 5 1/2 - 6 in hardness, while the pieces containing chalcedony may be 6 1/2 or higher and often have a more reddish purple color and/or distinctive patterning.

[Probably pure Sugilite: translucent "gel" pair, opaque solid purple piece]

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[Sugilite/chalcedony mixes: showing reddish purple color, and in the center suite, a pattern sometimes called "leopardskin Sugilite"] This beautiful purple gem was discovered during mining operations for manganese in the 1970's, but it didn't begin to make a market impact until the 1980's. It is expensive as opaque stones go, even though the known deposit is quite large, this is primarily because the one and only source is remote (in the Kalahari Desert near Botswana), and it must be mined 3200 feet underground. I have no doubt that it would be buried still, if it were not a profitable sideline of on-going industrial manganese mining. In the early 80's, attempts were made to market Sugilite under various tradenames such as "Royal Azel", "Wesselite" and "Lavulite", but none of these caught on. The translucent, dark purple (grape jelly) pieces are referred to as "gel Sugilite" and are very expensive due to their rarity. It's estimated that less than .05% of the gems mined from the deposit are in this gel form. The gem has recently received a boost in popularity, though, as have many unfamiliar opaque gems, via the home shopping channels and internet auctions sites which feature them in sterling silver jewelry. There are no known enhancements of this gem and it has not been synthesized. However, a plastic "Sugilite" simulant is sometimes used in inexpensive jewelry pieces. Plastic will melt and give off an acrid smoke when touched with the tip of a red hot needle, Sugilite will not react.

Care

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Athough reasonable care should be taken in setting and wearing this gem, it is relatively durable compared to some other popular cabochon gems. Sugilite is, for example, less susceptible to chemical attack than turquoise, and less sensitive to heat and drying than opal. It will need a repolishing from time to time if worn daily in a ring, and it should be protected from sharp knocks, but otherwise it is highly suitable for most jewelry uses.

[Sugilite mounted in silver: a lovely combination!]

Value The major value points are the depth and purity of the purple color and the degree of translucence. Within the opaque type, those which are the richest and purest purple color (without appearing black) and least mottled are the most valuable. It is the translucent "gel" form that commands the highest prices -- the very best pieces of which are generally set in gold and surrounded by diamonds . When pieces are mottled, particularly attractive patterns can rise above the norm in value, as is the case, for example, with the spotted "leopardskin" Sugilite.

Gemological Data: Makeup: a complex silicate colored by manganese, often mixed with chalcedony (quartz) Hardness: 5 1/2 - 6 if pure, 6-6 1/2 if mixed with chalcedony Crystal structure: hexagonal Cleavage: none Density: 2.74 505

RI: 1.60-1.61 if pure, can be as low as 1.54 from chalcedony present Birefringence: .003 Pleochroism: none

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Malachite Gems like malachite, which are stunningly beautiful, yet common and inexpensive, always bring to my mind the "No respect" phrase made familiar by Rodney Dangerfield. Pretend for a moment that there were just a handful of specimens to be had, think how we would sing its praises, and long to own one. Despite ready availability, though, malachite has a great deal to recommend it to the gem lover, or to anyone simply interested in Nature's wonders. Our forebears valued the dramatic colors of this mineral not only for use as an ornamental material and a gemstone, but also in ground form as a cosmetic (eye shadow). Unfortunately, although the results may have been beautiful, they were also hazardous to health: the copper content of the dust released from grinding this stone makes it toxic to breathe. (Today those workers involved in the mining and fashioning of malachite are advised to wear protective respiratory gear, and to keep dust to a minimum by keeping the rough wet.) There is evidence that malachite was mined in Egypt as early as 4000 BCE. Early on it was ground and used as a pigment for paints. Not until the industrial revolution were synthetic pigments created that could rival the green hues achieved this way. Those who restore and conserve old paintings still use the old malachite based formula for authenticity. There is disagreement in the mineralogical literature as to the derivation of the name. Most writers agree that the word comes from the Greek, but there is a split between those favoring malakos meaning soft, and those who propose malakhe meaning the green herb, mallow, a reference to the color. Invariably associated with deposits of copper ores (and itself considered to be one of the minor copper ores at 58% copper content), malachite recovery is generally done, at least on the large scale, as a sidelight of copper mining.

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[Typical malachite rough] This vivid green gem gets its color from the copper in its chemical formula, and its lovely swirling and concentric patterns, from the way forms. The basic mode of formation is precipitation from solution, rather than from the crystallization of melted rock, or from the condensation of vapors. Technically malachite is termed a "secondary" mineral which means that it is created by a chemical reaction between minerals that have already formed, rather than by a simple one-step process. When waters containing carbon dioxide or dissolved carbonate minerals interact with preexisting copper-containing rocks, or, alternately, when solutions containing dissolved copper minerals interact with carbonate rocks, malachite may form. Most commonly it occurs in "massive" form as a micro-crystalline aggregate, in nondescript lumps, or as crusts on other rocks. The typically banded appearance reflects the waxing and waning of the solutions necessary for formation, and the frequent changes in their chemical content. The majority of the world's malachite supply comes from The Democratic Republic of Congo (formerly Zaire), Namibia, Russia and the American Southwest. Due to its softness it is easy to shape and carve, but unlike many soft minerals, it generally takes a good polish. With attributes like this, there is no wonder that it finds so many decorative uses. Perhaps the greatest malachite appreciators of all time were the Russian Royals of the 19th century who had sets of dinner ware, huge sculptures, vases and even sections of room paneling made of it. Here's a link to a virtual tour of the famous "Malachite Room" of the Hermitage: (be patient it takes this mega-file time to download) http://www.hermitagemuseum.org/html_En/08/hm88_0_1_62.ht ml The Victorians were great admirers of opaque jewelry stones, and malachite was one of their favorites, which they sometimes chose to set in gold. For the most part today, though, this gemstone is used in small carvings, beads, and cabochon gems usually set in silver. It is particularly popular in both genuine Native American sterling designs and inexpensive imitations of them.

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[Victorian gold and malachite brooch, Victorian gold, malachite and natural pearl necklace: Image courtesy of www.fraleigh.ca, Native American style silvertone and malachite bolo, contemporary bead strand, malachite carving] The lovely colors and patterns, easy workability, and the ready supply of fine material also endear it to today's lapidary artists for use in intarsias and inlays.

[Intarsia and inlay using malachite] Mineral and gemstone collectors compete to acquire prime malachite specimens which show some of its rarer habits. Botryoidal masses, stalactites or slices cut from them, and specimens with splayed out clusters of needlelike (acicular) crystals showing a velvety chatoyance are highly prized.

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[Collector's Treasures: a botryoidal mass, a polished slice from a stalactite, tufts of needle-like radiating crystals with silky luster] Happily, along with malachite in those secondary deposits are other copper containing minerals which sometimes end up combined in the same specimens. Along with malachite's forest green, the addition of blue-green chrysocolla, dark blue azurite, or brick red cuprite can create rocks of surpassing beauty.

[Malachite and friends: with chrysocolla, with azurite, with cuprite] Enhancement Malachite is rarely enhanced, although lower quality, less compact pieces may be stabilized with plastic resins or given a surface polish with wax. Although synthetic malachite has been manufactured for research purposes, it has not much been found in the gem marketplace to date. There would be little point, as the synthetic material would be far more costly than the natural mineral which is in abundant supply. Value Malachite is plentiful in its typical forms, so even the best specimens are modestly priced. Pieces showing an unusual crystal habit, distinctive pattern, or chatoyance, will have higher values. Likewise, rocks consisting of malachite and other colorful copper minerals in lovely combinations generally command higher prices than do pure malachites. The value of 510

carvings and ornamental objects will hinge primarily on their size, and artistry of the work. Care Malachite is soft and somewhat brittle, and is sensitive to both heat and acids. It requires gentle care, so no ultrasonic or steam cleaning should be done. Use in rings, bracelets, belt buckles, or other jewelry that gets rough and/or constant wear is not advisable. On the other hand it is an appropriate and delightful gem for earrings, brooches, pendants, tie pins, and occasional wear rings or bracelets.

Gemological Data Makeup: Cu2CO3(OH)2 (a copperhydroxycarbonate) Crystal system: monoclinic Crystal habits: massive, botryoidal, rarely, small acicular (needle-like) crystals Refractive Index: 1.85 (average) Birefringence: 0.025 Hardness: 4 Toughness: poor Specific Gravity: 3.80 Polish luster: vitreous to silky Fracture: uneven to splintery Optical phenomena: rarely, chatoyance Fracture luster: dull UV Reaction: inert

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Turquoise As early as 4000 - 5000 BCE humans, first in the Sinai region of Egypt, and a millennium later in Mesoamerica and China, were mining and working turquoise into jewelry and ceremonial objects. It was so highly valued in Eqypt, that when high quality deposits were exhausted, artisans developed a copper glazed ceramic simulant called faience, rather than abandon use of that sky blue color in their artwork.

[Faience "Mummy" beads, circa 300 BCE] Chemically, turquoise is a hydrated copper/aluminum phosphate, of aggregate, cryptocrystalline structure. There is only one known deposit (in the state of Virginia) where turquoise is found in transparent to translucent discrete visible crystals. Specimens from that locale are rare and bring a hefty price from collectors.

[Small turquoise crystals (triclinic crystal system) from Virginia 20x] More typically, turquoise is found as an opaque deposit in nodules, or veins within host rocks, or as shallow crusts on the surface of rocks.

[Typical turquoise deposits: crust and veins in rocks from Nevada, portion of a larger turquoise nodule from Globe, Arizona] 512

Color ranges through shades of blue to blue-green to yellowish green depending on the amount of copper (adds blue) chromium or vanadium (adds green) and iron (adds yellow). There are rare specimens of blue-violet color which contain strontium impurities. In general, US mines produce slightly greenish blue, to green gems due to high iron and vanadium content. Most turquoise rough contains patches or veins of the host rock in which it formed, such as chalcedony or opal, brown limonite, black chert or white kaolinite.

[Color variation in turquoise is due to trace impurities and the nature and amount of the matrix] Such matrix can affect the color and toughness of the stone and its workability for the lapidary or jeweler. Relatively pure specimens of turquoise might have a hardness of around 5 and be moderately porous. In general, a high proportion of silicate minerals increases hardness and decreases porosity while a high content of clay minerals (like kaolinite) has the opposite effect. On one end of this spectrum, then, we find pieces of hardness 5.5 to 6 that take a bright polish and are minimally porous, and on the other end are pieces of a soft and chalky nature with so much porosity as to be unusable without stabilization. Turquoise occurs, usually in arid regions, where ground water percolates through aluminous rock in the vicinity of copper deposits. Like malachite, then, it is a secondary mineral which forms through the interaction of preexisting minerals and their solutions. Historically the finest material was obtained from mines in Persia (Iran), and there is still considerable production from that area, but the majority of today's commerce in turquoise is supported primarily by sites in North America, and China. Its name, from French, means "Turkish stone", a reference to the long history of imports of Persian material, through Turkey, to the West. The US deposits are almost exclusively limited to the Southwest with Nevada home to a larger number of mines than Arizona, New Mexico and Colorado

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put together. This is a source of pride for Nevada and turquoise is, in fact, its official State Mineral.

[Some important (historical and present) turquoise mines in the Southwest: Picture taken at the Las Vegas Natural History Museum] Historically, and to a large extent today, the most admired stones are those of a fine robin's egg or celestial blue color with no visible matrix (this shade is an indication that no iron and little vanadium is present). Historically, stones of this caliber were produced only in Persia (Iran), and some still are, but the world's supply is now supplemented by similar stones primarily from the US, such as those obtained from the Sleeping Beauty Mine near Globe, Arizona. It is common in the gem marketplace to call any pure blue, high quality material "Persian grade" regardless of its actual geographic origin.

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[Fine Iranian source (true Persian) turquoise, "Persian grade" turquoise from the Sleeping Beauty Mine] In the Middle East it has been traditional to set turquoise in gold, sometimes with diamonds. The Victorians also greatly admired turquoise, and generally set it in gold as well. In the US, though, turquoise has had a long historical association with silver jewelry. Long before the arrival of Europeans in North American, the native inhabitants had an appreciation for turquoise, which is still strong today. The significance of this gem for some tribal groups rivals the importance that the ancient Chinese gave to nephrite jade. Such was also true in South America, and the early Spanish invaders recorded their surprise in finding turquoise to be more highly valued by the native people than was gold.

[Victorian turquoise and garnet necklace in gold: Image courtesy of Acanthus Antiques, circa 1900 natural pearl and turquoise gold brooch: Image courtesty of www.fraleigh.ca, handmade traditional Navajo silver and turquoise bracelet: Image courtesy of www.irocks.com, contemporary commericial Southwestern style silver and turquoise design] During the 1960's and 70's there was a burst of admiration for turquoise among the US population, especially as found in Native American jewelry. After reaching the heights for a few years, this fad crashed amidst scandals involving simulants, imitations and "Indian" jewelry (even that being sold by some Native Americans ) which was made in Asia. The popularity of this gem is now once again at stratospheric levels, due to a combination of some well known modern designers favoring the stone, and 515

aggressive promotion by home shopping channels and fashion magazines. Although still widely available in traditional silver Southwestern style pieces, more and more designers are emulating the ancient Persians and the Victorians and setting pieces in gold.

[Contemporary turquoise jewelry using "Persian Grade" material in gold] The highest grades of turquoise are used for cabochons, carvings, and inlay, with the lesser grades finding use as polished beads or natural "nuggetstyle" beads.

[Turquoise carving and inlay] Among those who prefer the look of turquoise with visible matrix, the highest regard is generally given to material with an even, interconnected patterning of black matrix veins. Stones of this type are referred to a "spiderweb" turquoise.

[Spiderweb turquoise] Simulants and Enhancements There are numerous enhancements and simulants in the marketplace. All but the highest grades of turquoise may be "stabilized" by a pressure 516

infusion of wax or resin. Small, porous pieces are sometimes pressed together with a resin binder to make a stabilized mosaic. Although it is usually true that Chinese turquoise has softer matrix, and tends to be more porous than that from much of the American Southwest, the photos below show, stabilization or lack of it is not always obvious and it's dangerous to generalize.

[Closeup of stabilized mosaic slab showing areas of different colors, stabilized Kingman, Az turquoise, unstabilized Chinese turquoise] A relatively new electro-chemical enhancement called the "Zachary Process" has recently been promoted as an alternative to traditional stabilization, and is said to increase both durability and evenness of color. Some large retailers are now marketing gems treated in this way under proprietary brand names. Turquoise itself is infrequently dyed, but the white and grey-veined mineral, Howlite, accepts dye readily and is commonly found for sale. Unfortunately not all the dyed Howlite offered is properly labeled as "faux" turquoise. Howlite is sometimes sold in its natural state with the misnomer "white turquoise" --> but, make no mistake about it, there is NO such thing as white turquoise!

[A nugget of dyed Howlite sawn open to reveal its true nature, Howlite posing as the fictional "white turquoise"]

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In addition, there are numerous non-mineral imitations such as plastic, ceramic and glass, offered with or without matrix. Synthetic turquoise is also available, the most well known type of which was first produced by the Gilson company in 1972. A recent import from China, which is being sold as "yellow turquoise" (almost exclusively as beads) has been featured at some shows and by some retailers. The natural color is actually a light yellow-green, indicating high iron and low copper content, but, buyer beware, as some very bright sunshine or butter yellow dyed pieces are being offered without much effort to discriminate them from the unenchanced material. About the only natural gem with which turquoise is likely to be confused is variscite (which lacks copper), and which can look similar to green turquoise. Variscite and turquoise, in fact, sometimes occur together in a rock which has been dubbed "variquoise" which brings a premium price for its attractive patterns and combinations of colors.

[Variscite, "variquoise"] Care and Use As a gem material, turquoise has its limitations: it is relatively fragile, porous, and susceptible to heat and/or chemical damage. Turquoise averages 18 - 20% water content, and as the gem is heated (perhaps from an unwary jeweler's torch) that water is progressively lost until at 400 degrees C, the structural integrity of the mineral is destroyed. Few deposits of material are of such a fine grained and compact nature that they take a good polish and have low porosity. For these reasons, the majority of turquoise found in commerce today has been enhanced in one way or another. Even top grade, otherwise natural, stones are often given a surface coat of paraffin wax to seal them and enhance the polish. (Skin oils and cosmetic residues are prime culprits in changing and darkening the color of turquoise gems.)

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Due to this stone's properties, it is best to make turquoise rings and bracelets occasional wear items, and to protect all turquoise jewelry from heat, chemicals and shocks. So, no ultrasonic or steam cleaning, and wash only with mild, lukewarm soapy water and a soft brush, and wipe pieces with a damp cloth after wearing. There is an avid collector market for turquoise, with sibling rivalry amongst the various enthusiasts who see virtue in different colors, matrix variations and mine sites. Just as no gem collection would be complete without several representatives of this species, so no jewelry collection should be without at least one piece featuring this well beloved December birthstone gem. Value Considerations Evenness and saturation of color, would be the most important consideration in terms of value, followed closely by the degree to which the material is compact and capable of taking a good polish without stabilization. Among those who appreciate matrix patterns, the beauty of that pattern would be crucial in setting value. In my opinion, turquoise is a real gem bargain, for even the very highest grades of material are modestly priced compared to many other gems.

Gemological Properties: Chemical Composition: hydrated copper/aluminum phosphate (with varying amounts of iron, and other trace elements) Crystal System: triclinic RI: 1.61 - 1.65 Hardness: 5 - 6 depending on compactness and presence of other minerals Density: 2.60 - 2.90 (affected by matrix) DR: .040 Luster: waxy to vitreous Toughness: poor to fair

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Fossilized Plant Materials as Gems There are three main ways in which plants, or parts of them, can become fossilized so as to later be desirable as gemstones or ornamental gem materials: 1) they become compressed, compacted and altered over time, 2) they are replaced by mineral solutions 3) by slowly decaying in soft sediments they leave impressions or casts. 1) The Organic Plant Fossil Gems In some cases the original organic structures come to be buried by sediments, often in an oxygen-poor environment, where over time, high temperatures and pressures compact and compress them, while chemical changes are occurring which favor the formation of polymer-like or hydrocarbon molecules. The most familiar gem materials of this type are bog oak and jet, when the original material was wood, and copal and amber, when the original material was resin. Such gems are considered to be of organic origin as the molecules of which they are composed (although highly altered) are still largely those from the original living source. In general, the longer the period of burial, compression and chemical change, the more the characteristics of the material are altered. Bog oak comes from hardwood trees which were long ago buried in acidic peat bogs. The primary source for the material in use today is Ireland. Although considerable change in the character of the original wood molecules has occurred, bog oak, under magnification, still shows some graining and other signs which reveal its woody nature. Jet, which comes from far older buried wood deposits, has undergone substantially more change, and retains no such outer signs. Physically, jet is more stable and compact and takes a better polish than bog oak. The main sources for the jet in today's gem market are England and China.

[Victorian Era bog oak brooch and jet bracelet] 520

Copal and amber have a similar relationship in that they both originated as resin secreted from trees, but copal being much younger is less compact, hard, and stable than is the far older amber. The really interesting situation with amber and copal as plant fossils, is that they can have other plant fossils inside them! Pollen grains, bits of bark and leaf debris are very common, and mostly go unnoticed and unidentified in fossil resins, but the occasional intact leaf or flower makes a notable find.

[Baltic amber, copal with fossil debris likely to be of plant origin, microphotograph of a bryophyte (moss) fossil inside Dominican amber: Image courtesy of www.ambercompany.com] 2) The Mineral Plant Fossil Gems Although the source of "petrified" plants was, indeed, the original living object, those molecules have long since decayed away, and have subsequently been replaced by minerals from the surrounding environment. As a result, such gems are not classed as organic, but rather as mineral gems. Petrifaction, then, is the process in which, particle by particle, structures of a dead organism are replaced by mineral solutions, usually silicon dioxide. As a result, a perfect replica of the organic material is produced in agate, chalcedony or opal. If the original object was a woody plant the resulting stone is called petrified or fossilized wood. Technically this should be referred to as "a chalcedony pseudomorph after wood" but outside of academic circles, "petrified" will do just fine. Petrifaction is almost exclusively limited to the "hard" parts of plants such as wood, cones and seeds.

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[15' long petrified tree trunk with close-up of surface]

[Slices of petrified wood from Oregon: Image courtesy of Las Vegas Jewelry and Mineral] Huge deposits of brightly colored pieces have been found in Northern Arizona with black, red or yellow silica colored by iron or other trace minerals. Depending on the orientation of the slice and the conditions of petrifaction, there may or may not be clear annular rings or other woody structures visible. Most of this material is used for specimens or ornamental objects such as bookends, and in comparison, relatively few pieces are used for jewelry.

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[Cabochons with and without clear annular rings]

[Cabochon of petrified wood in a custom pendant, rare specimen of chromium colored petrified wood from Arizona] Rarer types of wood such as palmwood and tree fern wood are also seen and are favorites with collectors and jewelry designers as well. The interesting patterns that appear in such pieces may reflect the internal anatomy of the tree, such as that of the layout of the vascular bundles through which water is conducted from the roots to the leaves. Depending on the orientation of the slice such features could appear as rings, parallel lines, dots or streaks. The special case of "peanut wood" is interesting in that it is the petrified remains of wood buried in marine sediments which before petrifaction had been infested with a burrowing mollusk. The silt filled burrows of those wood parasites also fossilized leaving the "peanut" shaped markings.

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[Cabochons of petrified"peanut" wood, palmwood, tree fern wood] Also included in this group of petrified hard parts would be roots, bark, burls, cones and other such tree or plant structures. When the organic/mineral replacement is complete, these pieces are as hard as any agate or chalcedony, and are suitable for jewelry use with no special care necessary.

[Fossilized pine bark and palmwood burl]

[Cabochons cut from fossilized pine cones] 3) Impressions/Casts Yet another way that plant parts can become immortalized in stone is by leaving an impression. When very fine, soft sediments quickly cover fleshy organic parts of plants such as leaves, these can decay very slowly in the, now, oxygen-poor environment. This slow decay allows them to leave stains upon, or even actual casts of themselves, in the forming rock, as the silt and mud slowly compact and harden around them. Later, such rocks, which tend to split easily along layers, may be opened to reveal beautiful evidence of the once buried plant structure. These specimens are more delicate than petrified gems, but with care, many can be used in jewelry.

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[Fossil cast of fern leaves, an impression of a fern leaf, an impression of a red wood leaf] Not Fossils Some natural mineral inclusions look very plant-like and can, at first glance, be mistaken for fossils. Examples would be the tree and moss like inclusions of iron oxide and manganese oxide that invade cracks within crystals, or between rock layers to form branching crystalline structures known as "dendrites".

[Dendritic agates and a dendritic sandstone piece] Value It is hard to generalize about such a highly diverse group, but one cannot go wrong to say that the rarer, more perfect, and beautiful the fossil, and its state of preservation the better. For petrified gems the highest value is attached to those pieces which are fully agatized with no soft spots or gaps and which are well proportioned, beautifully cut, and with an excellent polish. Fossil hard and soft woods are more common than palm or tree fern, and therefore less expensive.

Gemological Data: (given for petrified pieces which are mostly quartz) Makeup: silicon dioxide Hardness: 7 Crystal structure: Trigonal Cleavage: none Density: 2.61 525

RI: 1.53-1.54 Birefringence: .004 Pleochroism: none

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Birthstones The custom of wearing birthstone jewelry started in 18th century Poland and has spread all over the world. For some months there is but a single choice, other months have one or more traditional or modern alternates. Traditional Birthstones for English Speaking Countries with Alternates. January: Garnet Once available primarily as dark, reddish brown stones, the gem marketplace now offers beautiful garnets in every color, except blue. From bright green drusy uvarovite, to neon orange mandarin Spessartites, to pure spectral green Tsavorites and raspberry pink rhodolites, garnets are available in a wide price range and many cutting styles. With hardnesses ranging from 6.5 to 7.5, depending on the species, garnets are reasonably durable gemstones for most jewelry uses. Main sources include India, Madagascar, Russia, Australia, Sri Lanka and the USA. As there no gem treatments commonly used on garnet to enhance its color or other properties, it generally is safe to assume the stones are natural.

[Garnet: Spessartite, uvarovite drusy, rhodolite, Tsavorite]

February: Amethyst Long a favorite, purple quartz, or amethyst, is available in sizes from small to huge, and in colors from pale lilac "Rose d' France" to strongly saturated 527

"Siberian" purple with glints of red and/or blue. As well as faceted stones, it is possible to find lovely amethyst cabochons, carvings and beads. It is a durable gem (hardness = 7) for most jewelry uses. Brazil, Uruguay and Zambia are major sources in today's market. Most amethyst is heated to enhance its color, unless stated otherwise, you should assume stones have been treated. The heat induced color change is stable.

[Amethyst gems]

March: Aquamarine/ Traditional Alternate: (Bloodstone) Named for its resemblance to the color of sea water, beryl in hues of bluegreen to blue in medium dark to pale tones is called aquamarine. It can be found in a variety of cutting styles and makes a brilliant and durable jewelry stone (hardness = 7.5). Virtually all aquamarine has been heated to reduce green tones and produce a purer blue, a change which is stable. Main sources are Brazil, Zambia, Madagascar and Nigeria.

[Aquamarine gems] 528

Bloodstone is an opaque dark green jasper with red spots. The main source is India. Like all jaspers, bloodstone is a durable, hardness = 7, gem for most jewelry uses.

[Bloodstone jasper]

April: Diamond With hardness of 10 and the brightest luster of all tranparent gemstones, diamonds have a unique place in the gem world. Diamonds occur in colorless and near colorless forms as well as rare fancy colors. Both color enhanced and synthetic diamonds are available as well as many diamond simulants, chief among them being cubic zirconia. Major sources include South Africa and Australia.

[Brilliant cut diamonds, diamond earrings, white and black diamond pendant]

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If diamonds are too costly, any colorless gemstone can be used as an "unofficial" alternate. Examples would be white sapphire, white topaz, Goshenite (white beryl), petalite, phenakite, Danburite, white zircon or rock crytal quartz. Depending on the species, hardnesses vary, but most make reasonably durable jewelry stones. Below are some colorless natural gemstone choices.

[Danburite, phenakite, rock crystal quartz]

[White sapphire, white topaz, white zircon]

May: Emerald Beryl with medium to medium dark green color, contributed by chromium or vanadium content, is called emerald. Although frequently visibly included, traditional oiling treatments enhance the clarity of most pieces. With hardness of 7.5 they make reasonably durable gemstones, oiled stones, however, require gentle cleaning with no solvents, steam or ultrasonics. The world's highest quality gems come from Colombia but Brazil, Zambia and Russia also contribute stones to the marketplace.

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[Emerald gemstones]

June: Pearl / Traditional Alternates: Alexandrite, Moonstone Pearls are one of the few gemstones of organic rather than mineral origin, and also one of the few identified almost exclusively with one sex (female). Historically, however, there was no sexual bias in appreciation of pearls. Today's pearls ("cultured") are joint products of mollusk and human cooperation, and can be from fresh or salt water species. Another unique characteristic is that pearls are the only gem commonly worn unfashioned (not cut or polished). Pearls are delicate gems that must be worn and cleaned gently. Fresh and saltwater pearls in many shapes, sizes and colors are available. Many different treatments might be used to enhance a pearl's quality or change its color, so unless otherwise stated, you should assume pearls to have been treated.

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[Cultured pearls: freshwater baroque, freshwater faceted pearl, Tahitian saltwater pearl ring, saltwater button pearl pendant, freshwater baroque cluster] Alexandrite is color-change chrysoberyl, and one of the world's most highly valued gem varieties. Few specimens of high quality are available, but the best of these show a color change from raspberry red to teal blue-green when the light source changes from incandescent to fluorescent or daylight. Cat'seye forms occur. Synthetics and imitations are available at more modest prices. Alexandrite is generally untreated and makes a very durable jewelry stone (hardness = 8.5). Although, historically associated with Russia, today's sources are Brazil, India and Sri Lanka.

[Same stone, different lighting: daylight or fluorescent color on left, incandescent color on right] Moonstone is a type of feldspar that displays an optical phenomenon called "adularescence", a floating light over the surface, often called "shiller. They range from transparent to opaque and occur in a variety of colors. They are generally cut as cabochons or used for carvings, but especially transparent 532

pieces are sometimes faceted. The most valuable type is colorless with strong blue shiller. Some moonstones show a cat'seye or, rarely, a four rayed star. About as fragile as opal (hardness = 6), they should be treated somewhat gently. Virtually all moonstones are unenhanced.

[Moonstones: highest quality blue shiller moonstone, star moonstone, cat'seye moonstone, faceted white shiller moonstone]

July: Ruby Red corundum is known as ruby (while all other colors of that mineral are called sapphire). Chromium is the coloring agent. Large fine rubies are the most expensive gems sold in today's marketplace bringing prices considerably above that for diamonds of the same size and quality. The world's highest quality rubies come from Burma (Myanmar), although Kenya, Pakistan, Vietnam, Thailand and Madagascar are important sources as well. Ruby is a very durable jewelry gem (hardness = 9), that has generally been at least heat treated. Some specimens show a "star" effect (asterism).

[Rubies: faceted heart shaped brilliant cut, ruby earrings, star ruby, ruby in zoisite carving, ruby cabochon] 533

August: Peridot Peridot occurs in shades of limey to olivey yellowish green that are unique in the gem world. Major sources include the USA (Arizona), Pakistan, Burma and China. One of the minority of idiochromatic gem species, whose color is derived from its inherent chemical compostion rather than from impurities, (allochromatic) like most. It is a reasonably durable jewelry gem for most applications with a hardness of 6.5. There are no treatments commonly used to enhance peridot.

[Peridot gems: pear shape, trilliant cut in a pendant, concave cut trillion, peridot cabochon]

September: Sapphire/ Traditional Alternate: Lapis Lazuli Although commonly thought of as blue corundum, sapphire occurs in a wide color range, as well as in phenomenal form, as star sapphires. Currently sapphire is the world's most popular colored gemstone with the US leading in purchases. Sapphires, with a hardness of 9, are second only to diamonds in durability. Most sapphires have been heated to enhance color, but a large variety of more exotic treatments exist in the marketplace. Unless you are 534

guaranteed otherwise you should assume any sapphire you purchase has been enhanced.

[Sapphires: blue pear shape, fancy yellow heart, fancy oval pink, sapphire earrings, sapphire cabochon pair, white star sapphire, slightly chatoyant sapphire carving] Lapis Lazuli is a blue rock made of several different minerals with an average hardness of about 5.5. One of the world's most historically important gems, it's royal blue color often with specks of golden pyrite is highly prized. An opaque stone, it is most often used for cabochons, beads and carvings. Sources include Afghanistan and Chile. Most true lapis is unenhanced, but synthetic lapis and various simulants do exist in the marketplace.

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[Fine quality lapis gems]

October: Opal/ Modern Alternate: Pink Tourmaline Opal is one of the world's most popular and variable gemstones. It ranges in form and color from the bright red and oranges of Mexican opal to precious white, crystal and black opals through matrix and boulder types and to the transparent crystal opals. Somewhat fragile, with hardness of 6, many precious opals are offered in the marketplace as doublets or triplets. Precious opal is distinquised by a phenomenon called "color play". This is caused by diffraction and interference of light rays as they pass through opal's ultramicroscopic structure of tiny stacked silica spheres. Australia, Mexico, Brazil and the USA are major sources. Treaments to darken color and stabilize pieces are fairly common. Often thin slices of opal are made into doublets or triplets to improve their durability.

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[Opal gemstones: precious opal, blue opal, yellow opal, opal doublets in earrings, boulder opal, Mexican opal, crystal opal, black opal doublet] Pink tourmaline has gained popularity recently, and is available from many sources world-wide and in many shades from pale baby pink to darker pinks tinged with reddish, brownish and orangey hues. Tourmaline makes a durable jewelry gem (hardness = 7.5). Many tourmalines are heat treated, and a few types are irradiated, but the colors obtained are stable.

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[Pink tourmalines: round brilliant pair, cabochons in earrings, checkboard cut heart shape, oval cabochon, pair of carvings]

November: Yellow Topaz/ Modern Alternate: Citrine Since the advent in the market place, in recent decades, of heated and irradiated blue topaz, many don't realize that, historically, the color associated with this gem was yellow. To distinquish this color, the term "precious topaz" is used, with "Imperial" being reserved for specimens of precious topaz that show a particularly intense orangey to reddish color. It is a brilliant and hard jewelry gem (hardness = 8), but must be used gently as it has poor toughness due to its tendency to cleave. The major source of yellow topaz in world commerce is Brazil. Yellow topaz is commonly heat treated.

[Precious topaz gems, the color at the tip of the large stone is Imperial color] Citrine is yellow quartz, and although it does occur in Nature, the majority of the richly colored pieces in today's marketplace have been heated. Large, clean pieces are available, so this stone is popular with custom cutters and 538

carvers and is often available in spectacular cuts. At hardness 7 it is a durable gem for most jewelry applications. The major source is Brazil.

[Citrine gems]

December: Turquoise/ Traditional Alternate: Blue Zircon. Modern Alternates: Blue Topaz/Tanzanite (December presents the widest range of alternates for birthstone choices): Turquoise is an opaque blue, blue green or green gem often with black or tan matrix. Although once associated in the US almost exclusively with Native American silver jewelry, there has been a recent surge in interest in this gem by modern designers working in gold. Sources include USA, Mexico and Iran. Somewhat fragile (hardness = 6) and sensitive to exposure to chemicals, it should be treated with care. In the gem marketplace you will find stones that have been enhanced by various treatments that seal the surface, fill cracks, or change color. A great variety of synthetic and simulant gems are can be found as well.

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[Turquoise gems: Beads, cabochon set, greenish color material showing matrix, blue colored stones showing brown and black matrix, turquoise carving] Blue zircon has been heated to that attractive color from the natural orangey brown rough. Its saturated greenish blue color and top-notch luster and brilliance have led to recent increases in popularity and familiarity. It is a relatively durable gem with hardness of 7.5. The main source is Cambodia.

[Blue zircon gems]

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Within recent years blue topaz (irradiated and heated white topaz) and Tanzanite (blue-violet heated zoisite) have been promoted as alternatives to the traditional choices. Topaz is a durable jewelry gem (hardness = 8), but Tanzanite is rather fragile (hardness = 6.5) and requires gentler care. Most blue topaz originates from Brazil, and all Tanzanite comes from Tanzania.

[Blue topaz]

[Tanzanite] **(If you don't especially care for the stone(s) assigned on this list to your birth month -- never fear. By doing some internet searching on "Mystical Birthstones" [Tibetan], "Ayurvedic Birthstones [Indian] ", traditional gems for the days of the week , or gems associated with the various astrological signs, you have many, many additional choices!)

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Meteorites as Gemstones Although most of us are familiar with meteorites as interesting collector items, far fewer realize that they, along with some related specimens, can be beautiful additions to a gem or jewlery collection. The majority of the essay that follows was written by one of my colleagues at CSN, Dr. David Batchelor, a specialist in planetary geology. In Astronomy 103: The Solar System, one of the courses David teaches (in person and online through CSN's Distance Education Department), the topic is developed in greater detail. Irons, Pallasites, Tektites and Impactites in Jewelry Most meteorites are pieces of asteroids, which are leftover building blocks of the planets. The more common meteorite types are chemically and geologically primitive, and while their chemistry may offer a fascinating glimpse into the planet-forming process, they are both too fragile and too drab to be of gemological interest (most look like ordinary dull grey rocks). Nevertheless, there are some meteorites and related materials suitable for jewelry. Irons: A handful of asteroids grew large enough to differentiate; they had enough gravity to pull theiriron content away from the rock and down into a core. Iron meteorites, which are really alloys of iron, nickel, and other metals, are fragments of these cores.

[An iron meteorite in a freeform natural shape which might find a good home in a pendant] Their fascination as jewelry comes primarily from their Widmanstätten patterns, which are seen only after a piece is cut, polished, and etched with 2% nitric acid in alcohol. At the concentrations found in these meteorites, iron and nickel do not mix, but separate into two types of crystals; plates of the low-nickel alloy kamacite grow in octahedral shapes, with the highnickel taenite alloy filling in the spaces. Specimens from deeper within the parent asteroid have cooled more slowly, and their crystals grew larger. 542

Much of the gemological skill in fashioning these pieces comes from selecting a piece with appropriate crystal size, cutting it to display the pattern to advantage, polishing and etching it to bring out the pattern, and somehow protecting it from rust.

[This pair of earrings features both sliced and etched, as well as simple tumble polished nuggets of iron meteorites]

[Iron meteorite "cabochons" with larger and smaller Widmanstatten patterns. The piece in the 14k gold pendant has been rhodium plated to resist rusting]

[This group has been plated with 24k gold, another attractive way to protect the metal from rusting and corrosion while preserving the crystal patterning] Pallasites: The most beautiful of all the meteorites, the 50 or so Pallasites are iron meteorites with silicate rock inclusions, often of amber to pale-green olivine crystals, gemologically known as peridots. The Pallasites all come from the core/mantle boundaries of three different parent asteroids, and are 543

collectively named after Peter Simon Pallas, who described the first known example, found near Krasnoyarsk in Siberia. They can have intact olivine crystals large enough for jewelry use.These specimens are often sliced to give a stained-glass effect, or individual peridots are faceted.

[This magnificent (and really valuable) slice from the Esquierl Pallasite has large "phenocrysts" of peridot interspersed within the metallic matrix. Image courtesy of www.gemfrance.com]

[A sterling silver pendant featuring a polished Pallasite slice (seen with reflected light to show the metallic sections and with back lighting to reveal the peridot pockets, a pair of tiny gem peridots (1.3 mm each, .07 ct. tw) cut from a Pallasite meteorite.] This URL will take you to a photo of the largest faceted Pallasite peridot gem known to exist (1.5 ct.), http://www............ Tektites: When meteorites hit the surface at high speeds, the target rock, soil or sand is melted, and droplets solidify into glassy tektites. They occur in 544

four particular areas on Earth, three of which are centered around known impact craters. (The number of named tektite strewnfields has actually shrunk over the years, as what were previously believed to be separate field were found to be parts of larger fields spreading across multiple continents. The Bediasites from Texas and the Georgiaites from Georgia are now recognized as part of the North American strewnfield from the 34 million year old Chesapeake Bay crater. The Australites, Chinites, and Indochinites are now part of the Australasian strewnfield, for which no crater has been found despite a relatively young age of 600,000 years. And 1 MY old tektites from Africa and Australia are part of the Ivory Coast strewnfield associated with a crater at Lake Boumtwi in Ghana.) Although there is significant evidence they formed from craters on Earth, a handful of prominent researchers cite contradictory evidence and argue for an origin from craters on the Moon. Some of the prettiest tektites are from the strewnfield along Europe's Moldau river, associated with the 15 million year old Ries Crater in Germany. These "Moldavites" are a striking green, with surfaces apparently shaped by wind as they descended through Earth's atmosphere.

[Rough Moldavite and Chinese tektites showing, flattened, bubbly, rough surfaces]

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[Carved Moldavite, faceted Moldavites in pendant with iron meteorite, Chinese tektite as body of stickpin with South Sea pearl] Impactites: One of the most mysterious materials in this general group is called Libyan Desert Glass. Found in remote areas of the Sahara often in quite large pieces, Technically, the Libyan Desert Impact Glass samples aren't tektites, although they are also bits of glass formed by meteorite impact. Tektites specifically show aerodynamic shapes from reentry through the Earth's atmosphere. (Or entry, if you allow for the possibility of a lunar origin.) The more general term "impactites" includes tektites, melt glass, impact breccias, shattercones, or any bit of geologic evidence of impact.

[Faceted Libyan Desert Glass] This URL will take you to a picture and story about a recent archeological finding of a scarab gem, carved from Libyan Desert Glass among King Tut's jewelry:http://news.bbc.co.uk/2/hi/science/nature/5196362.stm Man-Made "Meteorite" Gemstone This is a bit of a stretch, but kind of fun. In 1893 a French scientist Henri Moissan began studying fragments of meteorites from Arizona's Meteor Crater. Dr. Moissan discovered microscopic crystals of quantities of a new mineral, today known as a form of silicon carbide. In 1905, this mineral was named Moissanite, in his honor. Although opaque, non-gem forms of silicon carbide could be found and/or manufactured and were used extensively as industial and lapidary abrasives (harness = 9.5), none of the transparent, single crystal gem type was made until 1995. Recently Charles and Covard Company has patented the production process and is offering the near colorless form of the gem as a diamond simulant.

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[A man-made Moissanite diamond simulant]

Value Factors As huge crystals are available, the value of gems or carvings from this material is almost entirely due to the beauty, interest or artistry of the piece.

Gemological Properties: Chemical Composition: SiO2 Crystal System: Trigonal RI: 1.54 - 1.55 Density: 2.65 Fluorescence: none Luster: vitreous Hardness: 7 Fracture: conchoidal Fluorescence: none

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