Gemstones of Tanzania by Gilay Shamika

Gemstones of Tanzania Identification Brochure Color, Transparency, Refractive Index, Specific Gravity, Spectrum, Inclusions and Rough Shape

Eng. Gilay Shamika

2013

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PREFACE

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emstones have little attention in Tanzania compared to precious metals. Precious metals especially gold, copper and silver are known to most of Tanzanians and the business of the same is booming on daily basis. For gemstones is different story. Few Tanzanians who know about gemstones. When you talk about gemstones, few people will refer to Tanzanite, Ruby and garnets only. But there are more types of gems in Tanzania. This compilation is aimed to provide knowledge of gemstones which are cheaply available in abundant compared to precious metals. On top of that, they also command higher price than gold. The knowledge also will help Tanzanians to venture into gemstones and hence diversification of minerals business. Rather than everybody thinking of precious metals, Tanzanians can now start thinking of gemstones. Tanzania is believed to be the second country with higher amount of gemstones reserves after Madagascar. Gemstones are available in alluvial form along the river banks, swamps, and natural dams and in the valleys where the gemstones are washed out from the mountains by rainfall drains. Umber valley in Tanga is among the famous valleys with alluvial gemstones. The compilation has shown the areas with gemstone reserves. This will help if somebody has found the gems at a certain area, he/she can refer to this compilation and see what kind of gemstones are found in that .Whenever you see any colored stone within your vicinity, think about gemstones and not just gravels or pebbles. Consult this compilation or any Minerals office for identification. You might be playing with a gem worth a millions of dollars! Talk to your children and ask them to fetch any colored stone along the river banks, swamps and dams during their normal bathing games. The adults during grazing and farming they may see such kind of stones. It is not a joke; the records show even Dr.Williamsons found diamonds from indigenous who were blind about diamond. The first diamond also at south Africa Kimberly, was found within the hand of child playing with it as a normal pebble stone and one geologist saw it and the story changes.Songea sapphire and Tunduru Alexandrite were discovered by missionaries. The people thought those stones are evil because they don’t look like normal stones. Rubies having red color, were thought to be bloody stone causing death and alexandrite which changes color from Blue/Green to red, were thought to have mysterious power. Therefore after arrival of Christianity, the Christians took those stones to the priests (missionaries) to play for them and curse the devil not to bring again those wicked stones. The priests were baffled and tell the Christians to keep bringing those evil stones……..!! Knowledge is power, be the first to get knowledge in every field, you never know when it will ripe. 2013


Philosophy of Gem Business and Diamond Poem For Gem Business Illiterates;

Gem Business is like Politics, And, Politics is like Gem Business. Most of the People buy Gems by just trusting the seller about the benefits and features of the merchandise (blind purchase concept). The Gem might be real or fake but they just trust the seller’s words and close a deal. Politics is the same; you just trust the politician’s words and vote for him/her. Both politics and Gem Business share the same trait…..’Trust.’ But for Gem Business Literates;

Gem Business is a Science And, Science means Reality Gems knowledge is a science which can be proved and confirmed, hence distinguished from politics. The one with knowledge of gemstones is equipped with different skills to identify and confirm what kind of jewelry/gem is. For him/her is not about trust but reality. The only way to get this science is either to join a college or through private studies, and get rid of being one of those who buy or deal with jewelry/gemstones blindly. Devote your time and go through the whole compilation and for sure you will definitely become ‘Gem Literate’.

Diamond Poem Diamond is Durable than any gem, Diamond is the most Desirable gem among others. And above all Diamond is a real Deal. And for sure; Diamond will never in any case let you into Desperation .

© Eng. Gilay Charles Shamika

2013


IMPORTANT TERMS IN GEMSTONES COLOR In science color is a result of light wavelength when an object’s surface responds to light. The object’s surface can absorb, transmit or reflect light. These responses are the ones which results to the color we see. Human being can only see wavelength between 750 and 380nm.In gemstones, color is the combination of hue, tone and saturation. Colored stones as the name itself signifies, color is the supreme criteria in judging and grading colored stone. The hue, saturation and tone in their totality pave a way to a premium.GIA has done a great job in expressing the real differences of those three terms and how to identify them. Hue: Hue is the color that we notice immediately like red, blue, yellow, or green. Saturation is the intensity of the hue present in a color sensation. Colors of low saturation are sometimes called weak, grayish or brownish while those of high saturation are said to be highly saturated, strong or vivid. Saturation and Tone are used to distinguish the ‘range of colors’ (range of hue) –is it deep blue, pure Blue or slightly Blue. Tone indicates the lightness or darkness of a color sensation. The scale ranges from 0 for pure black to 10 for pure white. Black and white and the grays between them are called neutral colors. They have no hue. Colors that have a hue are called chromatic colors. Colors that do not have a hue are known as achromatic. In ancient histories color is related with happiness, grief, sorrow or misfortunes. In Bible and Qur’an color also signifies something according to scriptures. In different ceremonies colour is the one which determine the event at glance. Once you see black colour and large crowd of people, you start thinking of something wrong. The flags of nations have different colours not by accident but they hold the means and ways of the struggle movements towards the independence.

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For colored stones; color is the one which mostly bear the value of a particular gemstone followed by other factors- 4Cs.

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TRANSPARENCY In common English a word transparency means Clearness, Simplicity, Openly, Explicitly, Precision and Intelligibility. For English natives it might mean different but the logic remains the same. The word ‘Transparency’ has gained momentum in contemporary politics both in international and national forums. It is either related to democracy or administration, for instance transparency in democracy practices or transparency in administrative decisions. Scientifically transparency means ability of material to transmit light. The gemstones which allow light to pass through and enable observer to see through (clear), the gemstones are said to be transparent. If totally the gemstone doesn’t allow light to pass through is said to be opaque. But there are other gemstones which are in between; Transparency – Ability to transmit light Semi-transparent – Capable of transmitting light with some distortion, so an object viewed through the material is indistinct. Translucent – Capable of transmitting and diffusing light so an object viewed through the material cannot be distinguished. Semi-translucent – Capable of transmitting light only through thin area usually at the edge. Opaque – Inability of transmitting light.

HEFT OF GEMSTONES: Heft means how heavy a gemstone is when you feel it in your hand. The heaviness of a gemstone differs according to their crystal formation.

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INCLUSIONS AND PHYNOMENA The meaning of Inclusion The inclusions are virtually materials other than original gemstones. They may be formed before, after or on the same time with the gemstones. Broadly is defined as; Any irregularity or dislocations in a crystal's lattice, or structure, marks of the crystallization phases, color striations, and internal fractures, which may be caused by internal stress or external pressure; Simply the material trapped within the body of a crystal which is different from the primary elements of the host crystal. Types of inclusions commonly found in gemstones    

Crystal’s feathers, needle like, cracks, healed fractures and included lily pads and foils. Individual pinpoints, included crystals, voids Clusters of included crystals, or voids Clouds of pinpoints

There are three types of inclusions, or processes, through which other materials can get into a crystal; Protogenetic Inclusions: These inclusions were already present before the host mineral was formed. The host mineral grew around them. Therefore they are older than the host crystal. Syngenetic Inclusions: Formed at the same time as the host mineral. These inclusions can be solids, liquids, or gases, or combinations of any of the three forms of matter. These inclusions are therefore the same age as the host crystal. Epigenetic Inclusions: These inclusions were formed after the host crystal was formed. These inclusions are usually either formed by exsolution or from the recrystallization of a fracture in a host mineral. They may also be liquid, solid, or gaseous. These inclusions are therefore younger than the host crystal.

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PHENOMENA Phenomena are unusual display of gemstones in response to light. It is optical effects caused by reflection, interference or refraction. The phenomena effects increase the price of the gemstones; customers like buying something two-in-one, normal gemstone and phenomenal gemstone when light is directed on a gemstone.

Types of Phenomena Effects Asterism: Appearance of a star on the surface of a gem when light reflecting from minute needle-like inclusions in a gem.

Adularescence: Appearance of blue-white light in moonstone caused by thin fibrous or layers in moonstone by diffracting, diffusing and interfering the light.

Aventurescence: Appearance of glittering spots of color caused by light reflections due to platelets inclusions.

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Chatoyancy: Appearance of cat’s eye resemblance on gemstone surface after light being reflected by minute parallel needle-like inclusions, fibrous or parallel tubes inclusions depending on the gemstones. In other word; Phenomenon of certain Cat's eye minerals which causes them to exhibit a concentrated narrow band of reflected light across the center of the mineral. Chatoyancy is almost exclusively exhibited on polished cabochons.

Color change: Change of color of a gemstone body when different sources of light are applied (incandescent and fluorescent).

Play-of-color: Appearance of flashes of spectral colors (rainbow colors) in opal when minute silica spheres in opal cause diffraction interference of light.

Iridescence: Appearance of interference colors seen in agates and other gemstones. But mostly, the term is for agates.

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Orient: Orient logically is iridescence phenomenon but when occur in pearls, is called orient. Therefore orient is iridescence in pearl.

Labradorescence: Appearance of broad color flash across the surface of Labradorite feldspar. This occurs when the thin layers in Labradorite cause light interference.

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REFRACTIVE INDEX (RI) Refractive Index (RI) is the ration of speed of light in the air (vacuum) to the speed of light in a medium. SINGLE REFLECTION (SR): Is the optic property of a gemstone to exhibits a single reading on the refractometer. The reading does not change even if you turn the gemstone on the refractometer. If you use the polarizing filter, when you turn the gem under the polarizing filter, the gem’s light reflection intensity remain the same. DOUBLE REFLECTION (DR): Is the optic property of a gemstone to exhibits a double/more than one reading on the refractometer - the maximum and minimum readings on the refractometer. The readings change as you turn or move the gemstone on the refractometer. If you use the polarizing filter, when you turn the gem under the polarizing filter, the gem’s light reflection intensity change.

GEM REFRACTIVE INDEX (RI) IS LIKE HUMAN FINGER PRINT The RI is the most useful method in identifying gemstones. Garnet and Ruby can be quickly distinguished by SR or DR. All Garnets are single reflective (SR) while Rubies are double reflective (DR). Gemstone’s RI is like finger print for human being. There is no way, a finger print of one human being to resemble with others. The same for gemstones; each gemstone has its own RI. It is only possible for RI of one gemstone to overlap with other gemstones and having the same birefringence but rarely to be the same.

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GEMSTONES SURFACE APPEARANCE Gemstones surface exhibit different appearance when cut and polished. The differences are contributed by texture and structure of the gemstones crystal latticehardness. Luster is the term used to describe how does the surface of faceted gemstone look like in reflected light. High luster: The gem surface shines like mirror. This includes diamond, hematite, and Zircon and demantoid garnet. Hematite luster is called Metallic: Mirror like luster Diamond Luster is called Adamantine: the highest luster for all transparent gems Demantoid garnet and Zircon Luster is called Sub adamantine: Not sharp like adamantine. Medium luster: The gem surface shines like glass or slightly like glass (Vitrous and Sub-vitrous).Most transparent gemstones belong to this luster. Low luster: The gem surface looks like Greasy, Resinous, Waxy and Dull. Sheen Luster: The shines of the gem occur just below the gems surface. The reflection is seen as if is inside the gem surface and look Silky/ Pearly.

SYNTHETICS AND SIMULANTS Simulant means naturally look like. These are gems which occur naturally and used to imitate other gemstones. For example colorless natural sapphire, quartz, topaz and rocky crystal are sometime used as diamond simulant, while; Synthetics are manmade gemstones with the same chemical and physical properties as natural gemstones they imitate. They are made in Laboratory.

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GEOMETRY OF ROUGH GEMSTONES 1.

Meaning of Geometry in mathematics

In mathematics geometry topic is among the difficulty. Is about how angles are related to shapes, area and lengths of an object. I remember in my Ordinary and high school it takes ages of time to understand this topic; especially the logic behind Angle of sine, cosine, tangents etc. The scientists also have taken centuries to find the simplicity of geometry calculation. The most complicated geometry involves curved, domed and circular objects. The early mathematicians struggled a lot and some discovered pie (π), Angle of sine, cosine, tangents and other constants to simplify geometry of those complicated objects. The discovery of Calculus to some extent makes life easy but for others is even worse……..! Archimedes takes not less than 20 years to find geometry of curved objects but he was killed before he completed his work. When roman police came to arrest him he said ‘please do anything to me but don’t disturb my circles’. His room was full of drawings of curved objects trying to find the easy way of calculating angles, areas and lengths. Curved and hanging bridges, domed and curved buildings, enjoy this topic in engineering and architectural calculation before erected.

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Meaning of Geometry in Gemstones

In gemstones, geometry means the same as in mathematics. It means a shape of rough gemstones (crystal shape). Each rough gemstone has its habit naturally (crystal shape). The occurrence of Moonstone shape is expected to be different from corundum and other gemstones. There are occurrences of seven crystal systems (shapes) in gemstone as summarized in the next pages;

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Source: http://www.realgems.org

1. Cubic or Isometric – It is assumed all sides and length to be the same but not always. Sometime octahedrons (eight faces) and dodecahedrons (10 faces) are found into this crystal shape. 2. Tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms. 3. Orthorhombic - like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms or dipyramids (two pyramids stuck together). 2013


4. Hexagonal - six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon. 5. Trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division. 6. Triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.

7. Monoclinic - like skewed tetragonal crystals, often forming prisms and double pyramids. This is a very simplified view of crystal structures

Some example of roughs with typical crystal system

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RUBY BACKGROUND

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uby Name History: The name ruby comes from Latin word ruber, which means red. In Sanskrit which is Indian language, ruby is termed as ratnaraj which means King of Gems.

Colour Ranges: Ruby comes from Corundum group. According to GIA, for the corundum to be called ruby, it should be deep, pure vivid red. This depends on the combination of hue, tone and saturation. But in other geographical area even pinkish, purplish or orange red sapphire are called rubies. Therefore the distinction depends on the geographical areas. But professionally deep, pure, vivid red is ruby. Varieties: Ruby and Sapphire are varieties of Corundum group. The difference is colour. Ruby is red while sapphire is Blue. Sapphire has other fancy colours, like Songea Orange colour, etc. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.762 to 1.770 Specific gravity (SG): 4.00 Hardness: 9 Moh’s scale Inclusions: needle like rutile inclusion, fingerprint inclusions, high or low relief inclusions, two phase inclusion, straight and hexagonal growth banding, angular color banding and twining lines. 2013


TREATMENT Heating: To improve color or clarity appearance Lattice diffusion: This is a process of heating ruby to very high temperature in the presence of a coloring agent. The aim is either to increase colour appearance, remove color or change to other colour. Fracture filling: Is a process of filling fractures of ruby by using oil or proxy resin. The purpose is to improve clarity and also hide fractures. Cavity filling: Is the same as fracture filling but cavity is large and filling it may result in weight addition. SYNTHETICS/SIMULANTS/IMITATION Imitation: Glass Confuse with: Spinel, Tourmaline, Garnets, Topaz

RUBY DEPOSITS IN TANZANIA Morogoro: Mwalazi, Ngongolo, Matabe, Mayote, Mvomero,Matombo,ulanga(chipa,mahenge,Lukande,Epauko) Dodoma: Winza, Malamo, Madengi,matumbulu,mlali,mleha,Kongwa(pandambili) and Mangalisa Tanga: Kalalani, Kofi Mountains and Umber River valley Manyara: Hanang (dudumera), Monduli ,Mundarara Kilimanjaro: Same (Lolobukoand North pare Mts) Pwani: Bagamoyo(mandera) Ruvuma: Mbinga (Likombe)

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SAPPHIRE BACKGROUND

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apphire Name History: Sapphire name originates from Greek work Sappheiros. Before Greeks mixed lapis lazuli and blue sapphire with one name ‘Sappheiros’ because both have the same color.

Color Ranges: Sapphire has many colours but when the word Sapphire is used alone it means sapphire with blue colour. Sapphire with other colour than blue (fancy sapphire) need to have pre-fix of color for instance, Orange sapphire, Pink sapphire, Purple sapphire. Varieties: Sapphire is a variety of Corundum with the same geological properties like ruby the difference being only colour. Ruby red while sapphire Blue and other colours – fancy sapphires (orange, pink, purple, colorless, grayish etc). The Orange sapphire from Songea Tanzania is among the expensive fancy sapphire after pink.

GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): 1.762 to 1.770 Specific gravity (SG): 4.00 Hardness: 9 Moh’s scale Inclusions: needle like rutile inclusion, fingerprint inclusions, high or low relief inclusions, two phase inclusion, straight and hexagonal growth banding, angular color banding and twining lines. TREATMENT Heating: To improve color or clarity appearance Lattice diffusion: This is a process of heating sapphire to very high temperature in the presence of a coloring agent. The aim is either to increase colour appearance, remove color or change to other colour. It creates any colour in Corundum.

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Irradiation: This bombardment of electrons which cause energy release. The process is used to change colorless corundum to yellow or orange. But the color is not permanent. It fades with time. Fracture filling: Is a process of filling fractures of ruby by using oil or proxy resin. The purpose is to improve clarity and also hide fractures. Cavity filling: Is the same as fracture filling but cavity is large and filling it may result in weight addition.

SYNTHETICS/SIMULANTS/IMITATION Imitation: Glass Synthetics: Flame fusion sapphire, Flux sapphire, Hydrothermal sapphire, Floating zone sapphire. Confuse with: Amethyst, Kunzite, Tanzanite, Spinel, Zircon, Topaz, Tourmaline, dAquamarine.Chrysoberyl, etc Fancy Sapphire Confuse with: Citrine, Alexandrite, Rhodolite garnet, Spessartite garnet, Malaya garnet.

SAPPHIRE DEPOSITS IN TANZANIA Lindi: Nachingwea Lumesule, Tunduru Morogoro: Mahenge Tanga: Umba valley Dodoma: Winza

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EMERALD BACKGROUND merald Name History: The name comes from Greek word meaning green

Color Ranges: Emerald has only green color; it is a beryl with green color. Variety: Emerald belongs to beryl group which has two varieties – Emerald and Aquamarine. Aquamarine is a blue beryl while Emerald is a green beryl. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.577 to 1.583 Specific gravity (SG): 2.72 Inclusions: the gem with the most cracks and inclusions; three and two-phase inclusions, fingerprint inclusions, liquid filled inclusions, tube and needle like inclusions, calcite inclusions, angular growth zoning, minerals/crystals inclusions. Hardness: 7.5 to 8 TREATMENT Fracture filling: filling surface-reaching fractures with colorless oils or resins. Almost 95% of Emeralds are fracture filled because the occurrence of emerald is associated with fractures and inclusions. SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Green glass, Synthetic spinel triplet Synthetic: Flux emeralds, hydrothermal emeralds Alternatives: Demantoid garnet, Tourmaline, Diopside, Jadeite, Peridot, Zircon, Tsavorite garnet, Alexandrite EMERALD DEPOSITS IN TANZANIA: Manyara: Mbulu Kagera: Karagwe –kyerwa Morogoro: Mt. Nguru Rukwa: Sumbawanga-Mponda

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AQUAMARINE BACKGROUND

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quamarine Name History: Latin name –water of the see due to its color being the same as seawater – light blue.

Color Ranges: ranges from light blue to dark blue and blue-green GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.577 to 1.583 Specific gravity (SG): 2.72 Inclusions: hollow or liquid filled tubes, fingerprints and two/three phase inclusions. It occurs also as eye-clean Hardness: 7.5 to 8 TREATMENT Heat treatment change light color aquamarine to get the desired dark blue aquamarine. Confuse with: Topaz, Kyanite, Tourmaline and Zircon

AQUAMARINE DEPOSITS IN TANZANIA: Ruvuma: Tunduru Manyara: Mbulu

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ZIRCON BACKGROUND

Z

ircon Name History: Persian language – golden colored

Color Ranges: It has wide range of color- colorless, strong blue, green-blue, yellow, brown, orange, red, violet. The most occurrences are strong blue and green-blue with green color component. GEM IDENTITIES AND GEOMETRY OF ROUGH There are two types of Zircon - Higher and Lower Zircon. Blue zircon is said to be with high properties – strong doubling and high RI. Green zircon is said to be with low properties – no doubling and may show SR with SG 4.5 to 4.70 or 3.95 to 4.20. Refractive Index (RI): DR OTL Specific gravity (SG): 3.90 to 4.73 Inclusions: any natural inclusions possible Hardness: 6.5 to 7.5 Spectrum: Zircon with blue hue usually shows a key line at 653.5nm (known as zircon line) with other lines up to 40’s. Confuse with: Aquamarine, Topaz, Chrysoberyl, Tourmaline, Idocrase, Demantoid, Hessonite, Diamond and Sapphire ZIRCON DEPOSITS IN TANZANIA Singida Kiomboi Iramba and Eshamwala Morogoro: Ulanga Tanga: Mashewa and Mavumbi Dodoma: Winza Mpwapwa Rukwa: Namanyere and Paramawe

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KYANITE BACKGROUND

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yanite Name History: Kyanite means blue.

Color Range: Kyanite has most occurrence color is Strong blue, sometime with tints of purple. It rarely also occur as colorless, blue-green to brown. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.716 to 1.731 Specific gravity (SG): 3.5 to 3.7 Inclusions: Any natural inclusions possible Hardness: 4.5 to 5.0 Moh’s scale Confuse with: Sapphire, Tanzanite and Amethyst KYANITE DEPOSITS IN TANZANIA Arusha: Monduli.Manyara: Kwaraha and Sidi Hill Morogoro: Idibo Kilosa Tanga: Makalingi, Kitwai, Hakichoo, Gologolo Kilimanjaro: Hedaru, Chabaruti, Chankunku Rukwa: Namanyere, Tambaluka, Kisi, Chala.

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TANZANITE BACKGROUND

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anzanite Name History: Since Tanzanite is only found in one source in the world, Tanzania East Africa. Tiffany & Co the main distributor decided to name it by referring to the country of origin.

Colour Ranges: Tanzanite crystal occurs as a transparent rough with different colours including brown, blue, greenish-blue and khaki. But the most common is the one with blue colour. Predominantly blue tanzanite is generally worth more than other hues. The deep blue (A- grade) is obtained by heating tanzanite in controlled temperature but also they occur naturally. Tanzanite has distinguished property of showing three colors at different angles (Trichrinic) Varieties: tanzanite comes from Zoisite group. Before discovery of Tanzanite the only Zoisite varieties known were Thulite and Anyolite. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.69 to 1.70 Specific gravity (SG): 3.35 Inclusions: Often inclusion free but can include fine needles, pinpoints and clouds. Hardness: 6.5 to 7 TREATMENT Heating: Produce colors that include light to dark Violetish blue and bluish purple, as well as pure blue. But these colors also occur naturally. Confuse with: Sapphire, Kyanite, Amethyst TANZANITE DEPOSITS IN TANZANIA: Manyara: Merelani Tanzania

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T

TOURMALINE BACKGROUND

ourmaline Name History: Tourmaline name comes from toramalli which means mixed gems in Sinhalese language of Sri Lanka.

Color Ranges: Tourmaline comes in a wide range of colors. It is believed to be a gem with widest color ranges of any gem species. Varieties: Tourmaline exists in six varieties categorized by their colours.

1. Rubellite tourmaline

3. Chrome tourmaline

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2.Indicolite tourmaline

4.Parti-colored tourmalines

5. Watermelon tourmaline

6. Paraiba tourmaline

GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.624 to 1.644 Specific gravity (SG): 3.06 Inclusions: color zoning, thread like inclusions, gas filled fractures. Hardness: 7 to 7.5 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION: Glass, Synthetic Ruby, Synthetic Sapphire, Synthetic Spinel Confuse with: Any gemstones because tourmaline has all colors. TOURMALINE DEPOSITS IN TANZANIA: Kagera: Karagwe –kyerwa Dodoma: Mpwapwa-Winza, Chamwino (Hombolo) Mtwara: Newala Tanga: Handeni-Makwere, Muheza (Ng’ombeni) Manyara: Kiteto

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ALEXANDRITE BACKGROUND

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lexandrite Name History: Alexandrite was first discovered in Russia in the early 1800's. It was named in honor of Alexander Nicholavich, who was later to become the Russian Czar Alexander II. Legend has it that the gemstone was discovered on the future Czar's birthday and named in his honor, though the factual nature of this is disputed.

Color Ranges: Blue in daylight and red/purple in incandescent light. Alexandrite is the highly regarded color changing variety of Chrysoberyl. The color of Alexandrite changes under different lighting conditions. If viewed in daylight, its color is greenish blue to dark yellow-green. If viewed in incandescent or candle light, its color is pink to red. Alexandrite is a very rare and highly valuable gemstone, and until recently was extremely difficult to obtain due to its rarity. However, new sources in Brazil and Tanzania have made this gemstone available and more mainstream on the gemstone market. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.744 to 1.755 Specific gravity (SG): 3.5 to 3.80 Inclusion: Not diagnostic – any inclusion possible. Hardness: 8.5 Confuse with: Color change Sapphire and color change Garnet ALEXANDRITE DEPOSITS IN TANZANIA Ruvuma: Tunduru

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CHRYSOBERYL BACKGROUND

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hrysoberyl Name History: Chrysoberyl is a hard, tough, and durable gem. Although lacking the fire of other gemstones, Chrysoberyl in its various forms can be quite valuable.

Color Ranges: Most Chrysoberyl gems are yellow, though some are brown, green, or orange. Varieties: Chrysoberyl is best known for its important varieties Alexandrite and Cat's Eye. Alexandrite is a rare and expensive form that exhibits different colors in natural and artificial light. Cat's Eye is Chrysoberyl that is polished into a cabochon and highly chatoyant, displaying a sharp line of light through the center of the stone. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.744 to 1.755 Specific gravity (SG): 3.5 to 3.80 Inclusion: Not diagnostic – any inclusion possible. Hardness: 8.5 Confuse with: Topaz, Tourmaline, Zircon CHRYSOBERYL DEPOSITS IN TANZANIA Ruvuma: Tunduru

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TURQUOISE BACKGROUND

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urquoise Name History: Tourques (Turkish Stone).

The name refers to French expression Pierre

Color Ranges: The color ranges from light to medium blue or greenish blue. It is often mottled and sometimes has dark splotches. But can also occur without being mottled or splotches. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): 1.610 to 1.650 Specific gravity (SG): 2.74 Inclusions: mottled with dark splotches recessed below the surface. Hardness: 5 to 6 Moh’s scale TREATMENT Impregnation with wax, plastic or dye added: To improve color, luster and durability. Backing with Epoxy resin: Adds thickness, strength and weight. SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitations: Glass, Plastic, Reconstructed turquoise Confuse with: Agate, Chrysocolla in Chalcedony, Jadeite, Lapis lazuli, Malachite and Nephrite. DEPOSITS IN TANZANIA Tanga: Muheza – Gerevi-Hills

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PERIDOT BACKGROUND

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eridot Name History: The name originated from Arabic word Faridat, which means gem. It is also called Olivine or Chryolite.

Colour Ranges: Occurs as brownish or yellowish green to greenish yellow GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR 1.654 to 1.690 Specific gravity (SG): 3.34 Inclusion of natural Peridot: Disc like liquid and gas inclusions commonly called lily pads. High relief black chromites crystal inclusions. Hardness: 6.5 to 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitations: Glass, Plastic, Synthetic sapphire, Synthetic Spinel Confuse with: Demantoid garnet, Emerald, Tsavorite garnet, Zircon, Topaz, Tourmaline, Jadeite, and Chrysoberyl. PERIDOT DEPOSITS IN TANZANIA Manyara: Mbulu- Kingiti Dodoma: Kibakwe Arusha: Leishaine Hill.

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APATITE BACKGROUND

A

patite Name History: Apatite in Greek means ‘to deceive’. Apatite confuses with tourmaline and has RI close to tourmaline which can deceive you.

Colour Ranges: Occurs in variety of colour ranges. Colorless, Pink, Yellow, Green, Blue and Violet. Apatite is a fairly uncommon gemstone, and you will only rarely see it offered for sale in the typical commercial jewelry stores. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR 1.634 to 1.638 Specific gravity (SG): 3.18 Inclusions of natural Apatite: crystals, needles, two and three phase inclusions. Hardness: 5 Moh’s scale Confuse with: Aquamarine, Topaz, Zircon, Demantoid Garnet, Tsavorite APATITE DEPOSITS IN TANZANIA Manyara: Hanang- Gallapo Tanga: Korogwe-Umber Valley Dodoma: Mpwapwa Mbeya: Chamloto Mtwara: Newala- Nagaga

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SPHENE BACKGROUND Name History: The name sphene comes from greek word meaning wedge Sphene since its crystal shape looks like wedge.

Colour Ranges: Sphene occurs in variety of color range from yellow, brown, green and reddish brown. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR OTL Specific gravity (SG): 3.52 Inclusions: All natural inclusions are possible Hardness: 5 to 5.5 Moh’s scale Confuse with: Demantoid garnet, Citrine, Apatite, and Tourmaline SPHENE DEPOSITS IN TANZANIA Tanga, Dodoma and Morogoro.

2013


TOPAZ BACKGROUND

T

opaz Name History; The source of word topaz comes from Greek Topazios,the old name of an Island in Red Sea which used to be a source of Peridot. Topaz was confused with peridot before advancement of gemstones identifications

kills.

Colour Ranges: The color ranges from Colorless, Yellow, Brown, Reddish, Pink and Orange Varieties: Topaz has no variety but just trade names Imperial Topaz: Medium reddish Orange. The most expensive topaz. Sherry Topaz: Yellowish brown or brownish yellow to Orange.name comes from the color of sherry wine. To get rid of confusion with citrine and smoky quartz, Topaz with this color range is also called precious topaz. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): 1.619 to 1.627 Specific gravity (SG): 3.53 Inclusions: Two and three phase inclusions, liquid inclusions in its planes Hardness: 8 Moh’s scale TREATMENT Heating: Changes some yellow, Orange, brown topaz to Pink Irradiation followed by heat: Produces various shades of blue from colorless.

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SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitations: Glass, Synthetic Sapphire, Synthetic Spinel Confuse with: Aquamarine, Citrine, Tourmaline, Sapphire, Smoky Quartz, Hessonite garnet, Morganite, Zircon, Kunzite, Spessartite garnet, Malaya garnet.

TOPAZ DEPOSITS IN TANZANIA Dodoma: Winza Mpwapwa Tanga: Handeni Kwendikundi Plain

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IOLITE BACKGROUND

I

olite Name History: Iolite means violet in Greek language. It is also sometime called Cordierite

Blue Iolite

Purple Iolite

Color Ranges: It ranges from light to dark blue, brown and violet. Since it is pleochroic, it shows different color from different viewing angles. Depending on the angle, iolite appears colorless, gray or yellow. Navigators are said to use iolite as light polarizer to locate the sun. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR 1.542 to 1.551 Specific gravity (SG): 2.61 Inclusions: Hematite inclusions, natural inclusions Hardness: 7 to 7.5 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Glass Confuse with: Blue Topaz, Amethyst, Sapphire, Tanzanite and Purple/Blue Scapolite

IOLITE DEPOSITS IN TANZANIA Manyara: Babati, Hanang

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S

SPINEL BACKGROUND pinel Name History: The name’s origin is unknown. This is due to spinel being under estimated and under appreciated by many people during early civilization. The confusion of spinel with Rubies draws back its popularity by being referred to ruby. It is among the rare gemstones and hence less known in a market.

Color Ranges: The color ranges from violet, blue, orange, red, pink and purple. Spinel in most cases appears red and found in the same sources with rubies. It can also appear as color change from grayish blue in daylight to purple in incandescent light. Varieties: No variety but it is believed that Spinel is the most synthesized gem used to imitate other gemstones in the market. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.718 Specific gravity (SG): 3.60 Inclusions: minute octahedral or negative crystals, alone or in fingerprint pattern; included crystals, iron oxide staining. Hardness: 8 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Synthetic Sapphire, Glass, Synthetic Ruby Synthetics: Flux and Flame fusion Spinel Confuse with: Garnets, Ruby, Tourmaline, Topaz, Aquamarine, Amethyst, and Kunzite. SPINEL DEPOSITS IN TANZANIA Morogoro: Mahenge, Ulanga Dodoma: Winza Ruvuma: Tunduru

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S

SCAPOLITE BACKGROUND capolite Name History: The name Scapolite is derived from the Greek words scapos, which means rod, and lithos, which means stone. The natural crystal often looks stick-like, hence it's name. Scapolite is a little known gemstone that can be quite beautiful. The most common colors are a nice yellow to orange to pink or violet. Scapolite is a distinctly fibrous gemstone and is often confused with amethyst, citrine, Chrysoberyl and golden beryl.

Color Ranges: occur in different colors including Colorless, yellow, pink, violet GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR 1.550 to 1.564 Specific gravity (SG): 2.60 to 2.68 Inclusions: Natural inclusions Hardness: 5.5 to 6 Moh’s scale Confuse with: Amethyst, Tanzanite, Iolite

SCAPORITE DEPOSITS IN TANZANIA Dodoma: Imagi, Tambi Tanga: Umba korogwe

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GARNET BACKGROUNDS During my study at Gemological Institute of America (GIA), garnet varieties identification was one of my weakness points. I know at a glance that, it is a garnet but which one……Pyrope, rhodolite, Almandite, Pyrope-Almandite, Hessonite etc!! My instructor Annie did a tremendous job for me to master garnet varieties identification. Eventually everything was on a right track and my classmates used to tease me --- King of garnet. In my practical Exam of 20 stones, I picked up three garnets and I was able to identify their varieties. Spectrum is the most useful tool for garnet varieties identifications, especially for those combined garnets.

Green garnet

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Red garnet


Mandarin garnet

Mali garnet

DEMANTOID GARNET BACKGROUND

D

emantoid Name History: In Dutch language, demantoid means Diamond like. It is called diamond- like because it shows flashes of rainbow color (fire) like diamond. Demantoid flashes are more noticeable compared to diamond.

Color Ranges: Green to yellow-green GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.88 (OTL) Specific gravity (SG): 3.84 to 3.91 Inclusions: Mostly with horsetail like inclusion (radiating needle-like inclusions, but not in all demantoid) Hardness: 6.5 to 7 Moh’s scale

SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Garnet and glass doublet, Colored CZ, Colored YAG Confuse with: Emeralds, Peridot, Tsavorite garnet, Tourmaline, Green Zircon, and Green Sapphire.

DEMANTOID DEPOSITS IN TANZANIA No discovery at present

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TSAVORITE GARNET BACKGROUND

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savorite Name History: The name refers to Kenya Tsavo National Park where the gem is abundantly found. Merelani area apart from being the only source of Tanzanite, it also host some Tsavorites.TanzaniteOneMining Ltd (TOML as it is called by TMAA) encounters the Tsavorite when mining Tanzanite.

Color Ranges: The color ranges from light to intense green to yellowish green. It is used mostly as alternative to Emeralds .Since the stone is not treated it is favored by many customers who like green color. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.740 (Can be low up to 1.735 Specific gravity (SG): 3.61 Inclusions: Fingerprints, graphite platelets, liquid and minerals inclusions and healed fractures Hardness: 6.5 to 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Synthetic Spinel, Synthetic Emerald and Glass Confuse with: Peridot, Tourmaline, Demantoid garnet and Emerald.

TSAVORITE DEPOSITS IN TANZANIA Manyara: Merelani, Simanjiro -Lemshuku

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GROSSULARITE (GROSSULAR/GREEN) GARNET BACKGROUND

G

rossularite Name History: The name grossularite in Latin is gooseberry.

Color range: Near-colorless, Yellowish Green or green. Tsavorite and green garnet (grossular) are all variety of grossularite. The difference is their color intensity. Tsavorite is medium light to dark green, while grossularite is light yellowish green. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): 1.735 to 1.759 Specific gravity (SG): 3.61 Inclusion: Fingerprints, graphite platelets, liquid and minerals inclusions and healed fractures Hardness: 7 Moh’s scale NB: Grossularite- andradite garnet (mali garnet) is Yellowish green also with RI 1.773 to 1.779 while with RI 1.773 to 1.779 and yellow only , is also Grossularite garnet

SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Glass Confuse with: Tsavorite, Tourmaline, Demantoid garnet and Emerald.

GREEN GARNET DEPOSITS IN TANZANIA Manyara: Simanjiro –Lemshuku Dodoma: Mpwapwa

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HESSONITE GARNET BACKGROUND

H

essonite Name History: The information about hessonite name is quite unknown. Whatever the meaning of the name it is, hessonite is a variety of grossularite garnet like tsavorite. It is also known as Cinamon Stone in market.

Color Ranges: medium to dark orange to yellow, yellow-green, brownish orange and colorless. NB: If pale call it grossularite not hessonite GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.740 (can go up to 1.755) Specific gravity (SG): 3.61 Inclusions: heat wave effect (looks like undulating growth, burnt area or some call it scotch in water effect) and rounded crystals. Hardness: 7 Moh’s scale

SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Confuse with: Citrine, Spessartite, Almandite, Zircon, Topaz, Orange Sapphire and Fire Opal. HESSONITE DEPOSITS IN TANZANIA Morogoro: Kilosa, Uluguru mount, Mngazi valley, kisitwi Tanga: Mlola Lushoto, Kilinga and Kihunza Handeni Ruvuma: Likombe Mbinga

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SPESSARTITE GARNET BACKGROUND

S

pessartite Name History: The name comes from Spessart which is a district in Bavaria State, German that was the first source of a gem.

Color Ranges: It is among garnet gem which is not red as most people know all garnets are red – but it is not. (Always with orange component). Spessartite color ranges from medium – light to dark Orange, yellowish, brownish or reddish Orange. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): SR 1.810 (OTL) Specific gravity (SG): 4.15 Inclusions: heat wave effect (looks like undulating growth, burnt area or some call it scotch in water effect) and rounded crystals Hardness: 7.25 to 7.5 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Synthetic Sapphire, Glass Confuse with: Citrine, Fire Opal, Spinel, Topaz, Tourmaline, Malaya Garnet, Carnelian, Amber.

SPESSARTITE DEPOSITS IN TANZANIA Ruvuma: Likombe Mbinga Morogoro: Kisitwi Kilosa, Kihunza, Mngazi valley, Uluguru Mts, Tanga: Mlola Lushoto, Kilinga Handeni.

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RHODOLITE GARNET BACKGROUND

R

hodolite Name History: The name derived from Greek words, rhodo, rose and lithos, meaning stone. Geologically, rhodolite is a mixture of Almandite and Pyrope garnets.

Color Ranges: predominantly purple but also occur in a range of light to dark purplish red through reddish purple. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.750 to 1.780 Specific gravity (SG): 3.84 to 3.88 Inclusions: Low relief crystals, needle inclusions, zircon crystals with strain halos. Hardness: 7.25 to 7.50 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Synthetic ruby and Glass Confuse with: Topaz, Almandite, Pyrope, Spinel, Zircon, Tourmaline, Ruby.

RHODOLITE DEPOSITS IN TANZANIA Manyara: Lelatema kiteto Morogoro: Uluguru mts, Mngazi Ruvuma: Likombe

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PYROPE GARNET BACKGROUND

P

yrope Name History: In Greek language, pyropos means fiery eyed. The gem was called pyropos (fiery-eyed) because of having glowing red color. Sometime in market is called Bohemian garnet.

Color Ranges: The color ranges from medium to dark reddish orange to purplish red. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.730 up to 1.750 Specific gravity (SG): 3.78 Inclusion: needle-like, crystals and irregular rounded crystals. Hardness: 7 to 7.5 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Synthetic ruby and Glass Confuse with: Topaz, Almandite, Rhodolite, Pyrope, Spinel, Zircon, Tourmaline, and Ruby.

PYROPE DEPOSITS IN TANZANIA Tanga: Mlola Lushoto and Kilinga Handeni Dodoma: Tambi Mpwapwa Morogoro: Kisitwi, Kihunza, Mngazi and Uluguru mts. Ruvuma: Likombe Mbinga

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ALMANDITE GARNET BACKGROUND Almandite Name History: The Almandite was named after the town of Alabanda in Asia which was a center for trading and faceting gemstones from different places.

Color Ranges: The color range from orange red through red to reddish purple. It is mostly fashioned as hollowed cabochons to increase color intensity- more reddish.

GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): SR 1.781 to OTL Specific gravity (SG): 4.05 Inclusion: zircon crystals having strain halos, high or low relief crystals and Needlelike inclusions. Hardness: 7 to 7.5 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Garnet- and- glass doublet Confuse with: Hessonite, Spessartite, Rhodolite, Pyrope, Spinel, Tourmaline, Ruby.

ALMANDITE GARNET DEPOSITS IN TANZANIA Tanga: Mlola Lushoto and Kilinga Handeni Morogoro: Kisitwi, Kihunza, Mngazi and Uluguru mts. Ruvuma: Likombe Mbinga

2013


OPAL BACKGROUND Opal Name History: Opal is the most colorful of gems. Its splendid play of color is unsurpassed, and fine examples can even be more valuable than Diamond. The play of color consists of iridescent color flashes that change with the angle at which the stone is viewed. This phenomenon is often called opalescence. The play of color may consist of large, individual flashes of color (known as schillers), or may be of tiny, dense flashes. The intensity and distribution of the color flashes is a determining factor in the value of an Opal.

Color Ranges: White, Colorless, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Banded, and Multicolored. TYPES OF OPAL: Opals are classified into two types; Precious Opal and Common Opal. Opals displaying play of color are known as Precious Opals, and opals lacking play of color are known as Common Opals. Varieties of Opal: There are many varieties of both precious and common Opals. Black Opal: Is the most desired and beautiful form of opal. It is opal with a dark blue, dark green or black background with a strong play of color.

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White Opal: Opal with a light colored body color (white, yellow, cream, etc.) with strong play of color.

Fire Opal: Opal with a transparent to translucent deep-orange red. Mostly fire opal does not show play of color. If Fire Opal displays play of color, it is then called Precious Fire Opal.

Opal Doublets and Triplets Opal Doublets: Are thin slices of precious opal glued onto a base with any material to increase hardness of opal.

Black layer glued onto a base. Opal Triplets: Are like opal doublets but coated with a thin layer or dome of clear Quartz on top of cabochon to make them more resistant to scratches. (Glued on bottom and on Top covered with thin layer of other transparent materials)

Black layer onto a base and thin transparent on top glued 2013


Crazing Problem: A condition whereby opal shows cracks internally or on the surface when opal loose moisture. It is advised to keep opal away from excessive temperature. But not all opals are affected by crazing. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): SR 1.450 Specific gravity (SG): 2.15 Inclusion: patches or dots of play of color. The pattern maybe in terms of small dots (pin fire), large patches (flash) or distinct patches known as harlequin. Hardness: 5.5 to 6.5 Moh’s scale SYNTHETICS: Gilson synthetic opal or other synthetic opal, under magnification they show snakeskin-like structure or known as chicken wire pattern. Synthetic opal also can show columnar structure vertically.

OPAL DEPOSIT IN TANZANIA Kigoma: Buhoro, Nyakitonto and Makere

2013


MALACHITE BACKGROUND Malachite Name History: The stone's name derives from Greek molochitis lithos, "mallow-green stone”. The mineral was given this name due to its resemblance to the leaves of the Mallow plant.

Color Ranges: green, bluish-green or greenish blue with bands GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): AGG 1.655 to OTL (use birefringence blink method) Specific gravity (SG): 3.95 Inclusion: distinctive green banded appearance Hardness: 3.5 to 4 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ Imitation: Glass, plastic Confuse with: Turquoise, Jadeite, Nephrite

MALACHITE DEPOSITS IN TANZANIA Dodoma: Winza Rukwa: Mpanda Mara: Kamba Hill Tarime Mtwara: Masasi Ntaka

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FLUORITE BACKGROUND

F

luorite Name History: Latin meaning flow.

Color Ranges: It ranges from yellow, green, blue and purple. Purple or blue are mostly banded with colorless bands. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): SR 1.43 Specific gravity (SG): 3.18 NET Inclusion: Color Zoning or Bands, it might be also parti-colored, all inclusions Hardness: 4 Moh’s scale Confuse with: Since fluorite has every color, it confuse with any gemstone. FLUORITE DEPOSITS IN TANZANIA Mbeya: Chunya, Tukuyu Rukwa: Mpanda

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MOONSTONE BACKGROUND

M

oonstone Name History: It is called moonstone because it has a white shimmer like moonshine. That optic effect is called adularescence. It can also show asterism (star effect)

Color Ranges: It is colorless to white with a whitish-silvery to bluish sheen called adularescence (bluish sheen against colorless body.)But can be orange, yellow or brown. Varieties: There are two moonstone varieties, Moonstone Orthoclase and Moonstone Labradorite Moonstone Orthoclase – blue sheen with colorless body while Moonstone Labradorite – sometime called rainbow moonstone, it has strong blue or multi-color sheen. GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR/AGG 1.518 to 1.526 Specific gravity (SG): 2.58 Inclusion: centipede like inclusions Hardness: 6 to 6.5 Moh’s scale

Confuse With: Blue chalcedony and glass imitation

MOONSTONE DEPOSITS IN TANZANIA Morogoro: Kilosa Gairo Dodoma: Mkoyo and Zoisa Kondoa

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SUNSTONE BACKGROUND

Sunstone Name History: The name refers to the color and glitteriest of the gemstone which look-like the sun.

Color ranges: The sunstone has different varieties but the common one is orange.

GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR/AGG 1.539 to 1.547 (sunstone Oligoclase) 1.518 to 1.526 (sunstone Orthoclase) Specific gravity (SG): 2.65/2.58 (sunstone Oligoclase/ sunstone Orthoclase) Inclusion: Reddish to Golden metallic platelets Hardness: 6 to 6.5 Moh’s scale Varieties: There are two varieties of Sunstone. Sunstone Oligoclase and Sunstone Orthoclase

Confuse with: Glass imitation, Plastic imitation

SUNSTONE DEPOSIT IN TANZANIA Morogoro: Mtimbila Mahenge and Kilosa Gairo Tanga: Mtae Hill Lushoto Kilimanjaro: Ugweno Mwanga

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AMAZONITE BACKGROUND

A

mazonite Name History : comes from amazone forest where it is believed to be mined for the first time commercially.

Color Ranges : Green to Greenish- blue GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): AGG 1.522 to 1.530 Specific gravity (SG): 2.56 to 2.58 Inclusion: mottled coloring with grid-like patterns Hardness: 6 to 6.5 Moh’s scale Confuse with: Chalcedony, Chrysoprase, Serpentine and Turquoise

AMAZONITE DEPOSITS IN TANZANIA Tanga : Luguruni handeni Morogoro : Kilosa Gairo

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LABRADORITE BACKGROUND Labradorite Name History: It was first discovered in Labrador, Canada and named after that area.

Color Ranges: Labradorite is a member of the Feldspar family with remarkable play of color, known as Labradorescence. The color usually ranges from gray-green, dark gray, black or grayish-white. Labradorite is composed in aggregate layers that refract light as iridescent flashes of peacock blue, gold, pale green or coppery red. The predominant blue varies within the light, displaying hues from deepest blue to various shades of pale, almost blue-green.

GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): AGG/DR 1.559 to 1.568 Specific gravity (SG): 2.70 Inclusion: Black-needle like inclusions, metallic looking platelets which cause Labradorescence and repeated twinning. Hardness: 6 to 6.5 Moh’s scale Confuse with: Rainbow moonstone

LABRADORITE DEPOSITS IN TANZANIA Kigoma: Kidahwe, Nyakitonto

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QUARTZ BACKGROUND

Quartz is among abundant gemstones on earth. The abundance of quartz is due to its formation, it is made by silica and oxygen (silicate oxide - SiO2). Since silica and oxygen are found everywhere on earth, quartz is also found everywhere. The formation of quartz varieties depends on the size of the silica (clay) which combines with oxygen in presence of favorable temperature and water. The silicate crystallizes either in macro or micro depending on the silica size. Therefore, quartz varieties are divided into two groups; Macro – crystalline quartz and Micro – crystalline quartz. NB: All quartz varieties are Uniaxial positive; Might show a bull’s eye or Airy’s spiral optic figure. Quartz also shows brazil-law twinning under crossed polarizing filters.

Macro- Crystalline Quartz Rose quartz, Citrine Amethyst Rock Crystal Smoky quarts Aventurine quartz

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Micro – Crystalline Quartz Chalcedony ; Chrysoprase Chrysocolla-in- chalcedony Onyx, Carnelian Agate ,Iris agate, Fire agate, Dendritic agate Bloodstone Jasper

ROSE QUARTZ BACKGROUND Name History: It is called rose quartz simply because, the color looks like rose flower.

Color Ranges: The color of rose quartz ranges from very light to medium dark pink. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: look cloudy due to fracture, never transparent (semitransparent to translucent) Hardness: 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Glass and Plastic Alternatives: Topaz, Spinel, Tourmaline, Ruby.

ROSE QUARTZ DEPOSITS IN TANZANIA Kigoma: Mbirira Kasulu Dodoma: Winza Mpwapwa

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C

CITRINE QUARTZ BACKGROUND itrine Name History: The name citrine is related to citrus fruit’s color.

Color Ranges: The color of citrine ranges from light golden yellow to reddish yellow. Most people confuse citrine with topaz of similar color.

GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: Color zoning, negative crystals, two and three phase inclusion, twinning Hardness: 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Glass and Plastic Synthetics: Synthetic hydrothermal quartz, Synthetic sapphire, Synthetic Spinel Confuse with: Topaz, Spessartite, Orange Sapphire, Carnelian, Amber, Chrysoberyl, and Tourmaline.

CITRINE QUARTZ DEPOSITS IN TANZANIA Morogoro: Rubeho Kilosa Dodoma: Winza Mpwapwa

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AMETHYST QUARTZ BACKGROUND

A

methyst Name History: No vivid information about amethyst name.

Color Ranges: The Amethyst color is purple. The finest amethyst color comes from Africa. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): SR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion Negative crystals, liquid, color zoning, two and three phase. Hardness: 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES Imitation: Glass, Purple synthetic corundum, Synthetic Spinel triplets Synthetics: Hydrothermal Confuse with: Topaz, Spinel, Tanzanite, Sapphire, Tourmaline, Iolite, Rhodolite garnet.

AMETHYST QUARTZ DEPOSITS IN TANZANIA Kigoma: Mbirira Kasulu Morogoro: Rubeho Kilosa and Tungi Dodoma: Winza Mpwapwa

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ROCKY CRYSTAL QUARTZ

R

ocky Crystal Name History: It is called rocky crystal because it looks like colorless crystal. The colorless, transparent variety of Quartz, free of any impurities, is known as "Rock Crystal". Flawless and very large cuts may be cut from Rock Crystal.

Color Ranges: It is colorless quartz. Name History: The name citrine is related to citrus fruit’s color. Color Ranges: The color of citrine ranges from light golden yellow to reddish yellow. Most people confuse citrine with topaz of similar color. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: needles, two and three phase inclusions, liquid crystals. Hardness: 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES

-No information at present

ROCKY CRYSTAL QUARTZ DEPOSITS IN TANZANIA Morogoro: Rubeho Kilosa Dodoma: Winza Mpwapwa Kigoma: Mbirira Kasulu

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SMOKY QUARTZ BACKGROUND Smoky Quartz Name History: Smoky Quartz is the brown "smoky" variety of Quartz. It ranges in color from light brown to black.

Color Ranges: It ranges in color from light brown to black.

GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: crystals, two and three phase inclusion, needles, Hardness: 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES -No information at present

SMOKY QUARTZ DEPOSITS IN TANZANIA

Quartz is one of the most common and varied minerals on earth, and its abundant throughout the country. Quartz is extremely common and is found in numerous localities throughout the world.

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A

AVENTURINE QUARTZ BACKGROUND venturine Quartz Name History: The name reflects the phenomenon effect caused by chrome mica inclusions which cause appearance of glittering spots of colorAventurescence.

Color Ranges: It is almost green but rarely yellow, gray and brown. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: chrome mica inclusions (tiny, disk-like, flakes or platelets randomly distributed) which cause Aventurescence phenomenon. Hardness: 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES

-No information at present

AVENTURINE QUARTZ DEPOSITS IN TANZANIA Quartz is one of the most common and varied minerals on earth, and its abundant throughout the country. Quartz is extremely common and is found in numerous localities throughout the world.

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CHRYSOPRASE BACKGROUND

C

hrysoprase Name History: the name comes from Greek language, meaning gold leek.

Color Ranges: It is almost yellowish green. GEM IDENTITIES AND GEOMETRY OF ROUGH Refractive Index (RI): AGG 1.530 to 1.540 Specific gravity (SG): 2.60 Inclusion: Not diagnostic Hardness: 6.5 to 7 Moh’s scale SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES -No information at present CHRYSOPRASE DEPOSITS IN TANZANIA Dodoma: Chamwino, Itiso-Haneti

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CHALCEDONY VARIETIES BACKGROUND

GEM IDENTITIES AND GEOMETRY OF ROUGH; Refractive Index (RI): 1.530 to 1.540 Specific gravity (SG): 2.5 to 2.6 Inclusion: curved, straight bands or layers. Hardness: 6.5 to 7 Moh’s scale

CHALCEDONY DEPOSITS IN TANZANIA: Dodoma: Haneti – Itiso Hill. Kigoma: Kasulu.

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AGATE BACKGROUND Color Ranges: All colors banded with curved or straight lines. Varieties: moss agate, fire agate, dendritic agate, iris agate

FIRE AGATE

Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60

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DENDRITIC AGATE


IRIS AGATE


MOSS AGATE


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ONYX


SARD


SARDONYX


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CARNELIAN


CHRYSOCOLLA - IN - CHALCEDONY


JASPER BACKGROUND


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BLOODSTONE


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PEARL BACKGROUND

P

earls are among the most ancient decorations used by human being.

Natural Pearl - Pearl that is formed from calcium carbonate secretions that forms naturally within a mollusk without any human intervention. This term is distinguished from the more common Cultured Pearls which are produced with human intervention. Cultured Pearl. Cultured Pearls are produced by inserting a foreign substance known as a nucleus within the body of an oyster or mussel, which in turn causes the organism to grow a pearl around the nucleus. Oysters are cultivated and harvested in mass numbers for the purpose of growing Pearls within them. Almost all Pearls currently available on the gemstone market are of Cultured Pearl.

VARIETY OF PEARLS. Freshwater Pearl - Pearl that grew in a non-saline environment in a freshwater mussel with a habit of forming in irregular “potato” like shapes. The most abundant form of Pearls because each mussel can produces up to 50 Pearl while saltwater oysters produce only one to three Pearls per oyster. Saltwater Pearl - Pearl produced by a mollusk such as an oyster in a body of saltwater such as the ocean. Akoya Pearl: Cultured Pearls with a white color and a consistent round shape and a mirror- like metallic luster. Sometimes are treated to look black or a very dark blue. South Sea Pearls: Pearls with large size, white and golden color Tahitian Pearl: Also known as “Black Pearl.” They range in color from green to blue, red, gold and black. Abalone Pearl These pearls are often an iridescent blue color and commonly hornshaped

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Overtone: Although Pearls are characterized by body color, they also have an “overtone.” Overtone is the word used to describe the glint of a Pearl in various lighting. Overtones are most apparent in saltwater pearls. Although Freshwater pearls have an overtone, it is not as prominent or exact as those found in saltwater pearls.

PEARLS DEPOSITS IN TANZANIA Along the Indian Ocean in Mainland and Zanzibar

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RARE BLUE STONES THAT LOOK LIKE

LAPIS LAZULI

Lapis Lazuli is a deep blue opaque gemstone with pyrite sparkling. Refractive Index (RI): 1.50 to 1.67 Specific gravity (SG): 2.40 to 2.90

SODALITE

White streak/ irregular white lines Refractive Index (RI): 1.483 to 1.487 Specific gravity (SG): 2.20 to 2.30

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SUGILITE

Refractive Index (RI): 1.607 to 1.610 Specific gravity (SG): 2.75 to 2.80

CHAROITE


AZURITE


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Reference 1.

GIA Lab Manual

2.

Gemstones of the World By Walter Schumann

3.

GIA Gem Reference Guide

4.

Gemstones Guide by Shazmin,2000

5.

Gems Picture credits: Google gemstones picture

6.

Gemstones Processing Steps by Eng. Gilay Shamika,2010

7.

http://www. Minerals.net

8.

http://www.realgems.org

9.

http://www.gst.go.tz

10.

http:// www.tmaa.go.tz

11.

Philosophy of Gems Business by Eng.Gilay Shamika,2013

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Gemstones of Tanzania by Gilay Shamika

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