Rocks and Minerals - A Golden Nature Guide

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A GUIDE TO FAMILIAR MINERALS, GEMS, ORES AND ROCKS

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by H ERBERT S . ZIM PAUL R. S H AFFER Illustrated by

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RAYMOND PERLMAN

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Professor of. Art, Un ivers i ty of I ll i n ois

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GOLDEN NATURE GUIDE

G OLDEN PRESS • NEW YORK Western Publishing Company, Inc. Racine, Wisconsin

FOREWORD

GOLD C RYSTAL

Noth i n g is as i m po rta nt in the natura l world as our own earth and the rocks ben eath our feet. So it was i n evita b l e t h a t the 'Go lden Nature Guides i n c l u d e a n i ntrod uction to rocks and m i nerals. The task of selecting, descri b i n g , and i l l ustrating minera ls, rocks, and geologic structu res has many i n herent difficu lties. We a re g ratef u l to our col­ leagues and to othe r ex perts who have h e l ped. May we pa rticu l a r l y tha n k mem bers of the Geology Department of the U n iversity of I l l inois: Drs. C h a p m a n , D roste, Grim, Hagn er, Henderso n , Merri l l , Wa n l ess, and Wh ite, and Drs. Co l l i nson, Swa nn, a n d Willman of the I l l i nois State Geo log ica l Survey for specimens a n d s l i d es, and for i n ­ formation a n d en couragement. S o m e specimens came from U n iversity of I l l i n o is Natura l History Muse u m a n d departmenta l co l l ections; s o m e f r o m W a r d ' s Natura l Sci­ ence Esta b l ishm ent. The gem co l l ections at the C h icago Museum of Natura l History were inva l ua b le. Fine Koda­ chromes were provided by Scott lewis. Maps ca m e la rge­ ly from information i n the Minerals Yearbook of the Bureau of Mines, and from other m a ps a n d p u b l ications of the U n ited States Geologica l S u rvey. H.S.Z. P.R.S. © C o p y r i g h t 1957 by Western P u b l i s h i n g Compa n y , I n c. A l l r i g h t s rese rved, i n c l u d i n g rights of reproduction and use in any form o r by any m e a n s , i n­ c l u d i n g the m a k i n g of copies by a n y photo process, or by a n y e l ectro n i c or mech a n i c a l d e v i ce, p r i n ted or written or ora l , or record i n g for s o u n d or v i s u a l reproduction or for use in a n y knowledge retri e v a l system or dev ice, u n l es s permission i n writing i s obta i n ed from t h e copyright propri etor. Pro­ d u ced in the U.S.A. by Western P u b l i s h i n g Compa n y, I n c. Pub l i shed by Golden Press, N ew Yo rk, N . Y. library of Congress Cata l o g C a rd N u mber: 6 1 -8326

CONTENTS INTRODUCTION

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4

What is in this book a n d how to use it.

. . . . . An i n troduction to the ea rth, its crust, a n d the rocks t h a t make it u p .

SEEING THE EARTH AND ITS ROCKS

ACTIVITIES FOR AMATEURS ............ .

Where a n d how to col lect, study, a n d iden­ tify rocks and m i n e rals.

5-9 10-13

14-30

IDENTIFYING MINERALS

Physica l a n d chemical p roperties, crystal form, h a r d n ess, cleavage, chemical tests. METALLIC MINERALS .................. .

31-60

The common m i n e r a l s that are sou rces of iron, a l u m i n u m , u r a n i u m , a n d other metals. NONMETALLIC MINERALS .............. .

I nc l u d i n g calcite, gypsum, vario u s fo rms of q u a rtz; g r a p h ite, asbestos, a n d m a ny others. GEM MINERALS ...................... .

V a l u e d m i n erals that a r e cut a n d polished. Precious, semiprecious, a n d sy nthetic stones. ROCK-FORMING MINERALS

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61-82

83-93

94-108

Minerals i m portant in the formation of rocks widespread i n the ea rth's crust. . . . . . . . . . . . . . . . . . . . . . . 110-120 lavas a n d rocks fo r m ed far u n d ergro u n d .

IGNEOUS ROCKS

SEDIMENTARY ROCKS .. . . .

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Their origins a n d the typical geologic struct u res associated with them.

121-132

. . . . . . . . . . . . . . . . . 133-140 Those altered from the a bove kinds. Their identification a n d geol ogic significance.

METAMORPHIC ROCKS

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MORE INFORMATION

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INDEX

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ROCKS IN DAILY U S E

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156-157

. 158-160

HOW TO USE THIS BOOK This is a g u i d e to oid you in identifying rocks a n d m i nera ls. But it is more than that. This book will a lso help you un­ dersta n d the im porta nce of rocks a n d m inerals in our d a i l y l ives. Hence y o u w i l l fi n d information on the uses o f m i n ­ era l s a n d m i neral prod ucts as we l l as a ids in identification . Ski l l i n identifyin g rocks a n d minerals comes with ex­ perience. Take this book on. h ikes, tri ps, and vacations. Visit collecti ng p laces, exami ne specimens, a n d try simple fi e l d tests. Rem ember that only the most common k inds of rocks a n d m i nera l s are shown i n this book. Even these may va ry considera b l y i n their physical properties. T h u m b through this book before you go out on trips. Read the introductory sections. Next, becom e fa m i l ia r with the pictures of m i n erals, rocks, and rock structures. This may e n a b l e you to identify some common rocks and min er­ als at sig ht. Maps o n some pages show where i m porta nt de­ posits a re located. Books l isted on p. 1 56 w i l l h e l p fu rtner, but loca l inq uiry is often needed to pin- point .locations. As you m a ke observation s a n d· co l l ect specimens, c h eck·· your book or make marg i n a l n otes for later reference use. I n the l o n g run, your records may be as i m porta nt as the specimens you col l ect.

THE EARTH AND I TS ROCKS SEEING ROCKS AND MIN ERALS is someth i n g hard

to avoid. You have to sta l k w i l d l ife and await spring fl owers, but every roadcut, bank, c l iff, excavation, o r q u arry exposes rocks a n d m i n era l s for you t o s e e . Learn to watch for outcrops, p l aces where bedrock is natura l ly exposed, as in ridges or c l iffs. Wherever erosion is ta k i n g p l ace, rock is soon e r or later exposed. Outcrops of rocks a re com m o n in many pa rts of New E n g l a n d and the Southwest. W here soil is th ick, a s i n the m i d d l e states, o n e may have to search for o utcrops a lo n g river va l l eys a n d on steeper h i l lsides. Ma n-made exposures of rocks and minerals a re often the best source of s peci mens. Look i n road a n d ra i l roa d cuts, in q ua rries, rock pits, d u m p piles around m i n es, a n d s i m i l a r p laces. Look with care. Ask permission before e n ­ terin g a q ua rry. Be a lert for new roads, bridges, or fou n ­ dations where excavation s expose fresh rocks. 5

SURFAC E F O RM

lava-ca pped butte

ROC K

made af rock­ l i meston e

M I N E RA L

contains m i n e ra l­ calcite

Look for Surface Forms These a re evident in the physica l forms seen o n the surface-hil ls, v a l l eys, cl iffs, a n d basins. Some forms and structures are associated with a partic u l a r type of rock and can be recog n ized at a dis­ ta n ce. Knowing forms and structu res does more than h e l p y o u fi n d rocks a n d m i nerals. It a i d s y o u i n inter preting t h e l a n dsca pe, s o t h a t you can read dramatic cha pters of the h istory of the earth. Rock structures a re dea lt with u n d e r rocks (pp. 1 2 1 - 1 45 ) . P hysica l geology treats them in g reater deta i l . Look for Rocks These are t h e materia ls of which the crust of the earth is made. They form the m o u nta i n s a n d u n d e r l ie t h e va l leys. Y o u s e e t h e m w h e n t h e y have been pushed or fo lded upward o r when they jut through s o i l to form a n outcrop. All m i nera l s occur with i n rocks, and often a re components of rocks. Rocks i n c l ude the so l i d bedrock a n d a lso the unconsol idated d e b r i s above it, cal led the mantle. Look for Minerals These a re the b ricks of which the earth itse lf is made. They a re inorga n ic chemical elements o r compounds (so me q u ite com p l ex) fo u n d nat­ u r a l l y in the earth. Beca use each is a chem ica l o r a m ix­ ture of c l osely related chemica ls, a m i n era l has f a i r l y d efi n ite a n d sta b l e properties.

6

What Is Behind It All is as mysterious as the ori g i n o f t h e u n iverse, t h e s o l a r system, and t h e earth.· Geology is the science of the ea rth and its h istory. Min era l ogy (the study of m i nerals) a n d petrol ogy (the study of rocks) are two divisions of the science of geology. The Earth is a ba l l of rock 7927 m i les in diameter, weig h i n g a b o ut 6.6 sexti l l ion tons. It is com posed of a dense core as heavy as iron and severa l massive rock lay­ ers-denser near the core a n d lig hter towa rd the surface. The ·c ontinents themse lves are islands of gran itic rotk (p. 1 1 1 ) fl oating on the denser, d a rker rocks w h ich u n der­ lie the ocean basins and go down perhaps 600 m i l es. Most of our eco n o m ic m i n e r a l s are i n the l i g hter gran itic rocks and rock der ived from them. I n the process of mountain building some of the darker rocks have come to the surface and ca n be seen . The Earth and Man are insepara b l e , even at the dawn of a n age of s pace trave l . It is im possi b l e to name a major i n d ustry which is not d i rectly or i n d i rectly depend­ ent upon rocks a n d m i n era ls. Min era l resources a re ex­ tre m e l y im porta nt, and the increased use of them is a di rect measure of progress. It is im poss i b l e to t h i n k of a time when d e pendence on m i nerals w i l l cease. New uses for mi nera l s open tech n o l o g ica l vi stas. Ura n i u m m i nerals, once odd ities, are now a source of energy.

fl i n t k n ife 1 4,000 B . C .

bronze k n ife 500 B.C.

iron k n ife ( bronze h a n d l e ) A . D . 200

E a r l y m a n made these weapons by u s i n g m i n e r a l resou rces.

Mineral Resources were i m po rta nt thousa n ds of years ago when men trekked h u n d reds of m i les to fl i nt q uarries. As men learned to make bronze a n d stee l , they became esse ntia l . The foss i l fue ls-co a l and petro leum­ a re the ones o n which we sti l l depend, a nd atomic en­ g i n es wi l l n eed ura n i u m , thorium, and s i m i l a r meta ls. Conservation of m ineral resources poses rea l prob­ lems, for most of these can n ever be replaced. We have a l ready beg u n to m i n e the ocean-our greatest d e posit of low-g rad e ore. Conservation of minera l spec i m e n s is a spec i a l case. In some s i n g l e deposits of rare m i nerals, the fi rst col l ectors have ta ken the entire supply. Carel ess co l ­ lectors ofte n spo i l fi n e materia l . When you go co l l ecti ng, remember to be considerate of others. li mesto ne q u a rry near Bloomi n g to n , I n d .

Riker m o u n t

M i n e r a l cobinet

ACTIVI TIE S FOR AMATEURS COLLECTING is the fi rst a n d m ost obvious activity for a nyone interested i n rocks a n d m i nerals. A n d we l l it might be, for the n umber of m i nera l species comes to a bout 15 00, a n d there are w e l l over a h und red k i n d s of rocks. A co l l ectio n e n a b les you to study, com pare, a n d a n a lyze m i nerals; hence y o u learn m ore a b o ut t h e m . It's fun to fi n d , b uy, a n d swa p specimens. C o l lecting takes you out-of-doors; it a l so paves the way for more serious stud ies i n science o r e n g i neering. Where t o Collect I n addition to the g e n e ra l places mentioned on p. 5, run down specific m i n era l l oca l ities near you. Becom e fa m i l iar with the books and magazines l isted on p . 15 6 a n d with p u b l icatio ns of your state geolog ica l su rvey. Minera logica l magazines ofte n l ist m i nera l loca l ities, a n d in m a n y states g u i d es to m i neral deposits are ava i l a b l e . Ask m i neralog ists a n d l oca l col­ l ectors. They will be g lad to h e l p you out. How t o Collect i n vo lves the p l ace you g o to. A co l l ecti n g trip s h o u l d have s pecific o bjectives. Study the area i n adva n ce to learn the lay of the l a n d , accessi b i l ity, rock structures, a n d poss i b l e m i n era ls. A l l ow a m ple time. S u it your plans to the location. I n deserts, co l l ect early or late; m id d a y s u n o n bare rock can be overpoweri n g . Wo rk systema tica l ly; don 't attem pt too m uc h .

9

Equipment can be s i m p l e : a p i l e o f o l d newspaper for wra p p i n g specim ens, a n otebook and penci l, are a l l you need a t a m i n e d u m p, where materi a l i s broke n . Otherwise, a geolog ist's p i c k o r plasterer's ham mer i s essentia l-a n d g et a g o o d one. A co l d c h i s e l , a m a g n ify­ ing g lass, com pass, heavy g l oves, a pocket k n ife, and a shoulder bag or k n a psack a re usef u l . D o n 't carry too much. You w i l l n eed water and l u nch-a n d a kna psack f u l l of rocks gets h eavy. The Specimen You Collect should be selected with ca re. From a dozen that seem l i kely, keep o n l y a few. Hand-sized specimens are preferred. Some col l ectors look for s m a l l , perfect, thumbnail -sized specimens and study them with a l ow- power m icroscope. Be sure your specimen is fresh. Trim it to s h a pe . This takes skil l-you soon learn that l i g h t b l ows p laced correctly do the trick. Wra p your specimens as shown be low. I nclude a l a b e l with field iden­ tification, l ocation, a n d date.

10

SPECIMENS AT HOME take up room a n d gather dust.

Col lecting is fun, but g ive some thought to what you wi l l d o with your col lection. Some rocks a n d m i nera ls are so attractive that you may wa nt them for their sheer bea uty. Set these w h e re you can see a n d enjoy them. But if you i nte n d to have a stud y col lection, more is req ui red. As a fi rst step each spec imen m ust be accurate ly identified, classified, a n d la beled . Identification is best made by the p hysical char­ acteristics of m i nera ls a n d rocks ( p p. 13-24 ) . C h eck the hardness, streak, specifi c g ravity and, poss i b l y, the crys­ ta l form. Often the geo log ist at the state u n iversity, mu­ seum, or geologica l survey will identify difficult specimens. Send h i m a s m a l l sample with exact deta i l s of where it was fou n d . Classification o f rocks a n d m i n erals d e p e n d s o n yo u r purposes. I n this b o o k f o r beginners, a very s i m p l e classi� fication is used. More advan ced books fo l l ow a sta ndard chemical c l a ssifi cation for m i nera ls, a n d a more d eta iled c l a ssification of rocks. C lassifi cation goes o n e ste p beyo n d identifi catio n . It shows you t h e re lationship between rocks or m i nera l s. That poi nts the way to discovering their origin, h isto ry, a n d m odes of occurrence. Labeling usua l ly beg ins with a spot of q u i ck-drying enamel put o n the specimen in a n inconspicuous p l ace. After it dries, a n u m ber is a d d ed i n I n d ia i n k. T h is number refers to a l a b e l a n d a cata l og, both of w h i c h should i n ­ c l ude n u m ber, n a m e, location, collector, date, a n d rock or m inera l associations.

11

AGATE

shaped sectio ns

po lished

mou n ted

OTH ER ACTIVITIES re lated to rocks a n d m i nerals in­

c l u d e the a rt and science of gem co l l ecti n g a n d gem cutti n g . A n a mateur can co l l ect or purchase a n a b u n d a nce of semiprecious stones which he can cut a n d polish (p. 90) to bring out their br i l l ia n ce. From this it is o n l y o n e ste p to m a k i n g your own jewe l ry. Photogra p h i n g rocks a n d m i n era ls is a cha l l en g e t o t h e camera m a n . A cl ose- u p lens revea ls str i k i n g deta i l s of form a n d co lor. F i n a l ly, more experienced a m ateurs may wa nt to specia l ize i n the m i n ­ era ls o f t h e i r home loca l ity or i n certa i n grou ps, as t h e q u a rtz m i n era ls. Others may fi n d t h a t experime nts with fl u orescent ( p . 22) or radioactive m inera l s a re i m po rta nt e n o u g h to d e m a n d their u n d ivided atte ntio n . Mineralogy Clubs are so n u merous t h a t it is im pos­ sible to list them here. They are p l entif u l in the East a n d West, but a re by n o m e a n s lack ing i n the m i d d l e states. Some clubs specia l ize in gems, gem cutti n g , a n d polishing , but most a m ateur groups are concerned with a l l aspects of rocks a n d m i nera ls. Some a re for a l l , includ i n g beg in­ ners; a few are for adva nced students a n d professionals. All have meeti ngs, exh ib its, fi e l d tri ps, a n d sometimes their own l aboratories. Join a club if there is one nea rby. There is no better way to get started. 12

JAD E I T E is sod i u m a l u m i n u m sili­ cate ( NaAISi206 ) . Color: w h ite, yel low, brown, o r green. Ofte n a gem ( p . 88); seldom as crysta ls.

is l ith i u m a l u m i n u m silicate (liAISi206); o p a q u e­ white, l i lac, or yel low. Rarely a transparent crysta l l i n e gem stone. SPODUM E N E

IDENTI FYING MINERALS They a re chem ica l ele­ ments or com pounds fou n d natura l ly i n the crust of t h e earth. T h e y a re inorgan ic, in co ntrast t o org a n i c chem ica ls (made m a i n ly of carbon, hydrogen, a n d oxyg en) typica l of l iving things. Some m inerals have a fi xed chem ica l com position. Others a re a series of related com pounds i n wh ich one meta l l ic element m a y who l l y or partly re place another. The two m inerals a bove a re very similar chem­ ica l l y a n d i n some of their p hysica l prope rties, but a re usua l l y q u ite d ifferent in color a n d other physica l prop­ erties. On ly rarely will a s i n g l e physica l or c h em i c a l prop­ erty identify a m i n era l . Usua l l y more c h a ra cteristics m u st be used. These p hysica l a n d chem ica l properties are de­ scribed on pp. 1 4 to 24 . Some a re in herent a n d re liable; others a re varia b l e a n d m u st be used with care. You can easily learn to use the simpler physica l a n d chem ica l tests. Identifi cation of m a n y rare m i nera l s often req ui res ex­ pen sive l a bo ratory eq u i p ment and deta i le d c h e m i c a l a n d o ptica l tests w h ich only an ex pert can m a k e. MINERALS AR E CHEMICALS

13

SOD I U M ATOM

combines with

CHLOR I N E ATOM

by tra n sferring one electron per atom a n d fo rming a

sod i u m i o n ( N o+)

chloride ion (CI-)

which a re present i n sod i u m ch loride ( h a l ite, p . 68)

ELEM ENTS a re the b u i l d i n g blocks of a l l materials, in­ c l u d i n g m i nera ls a n d rocks. About 1 00 e l e m e nts are known. A d ozen or so were known i n ancient times; the latest were fou n d i n atom-splitting experiments. All are made u p of protons, neutrons, and e lectro ns. These, com­ b i n ed, form atoms of m atter. The atoms i n turn join to fo rm molecu les-the smollest pa rticles usually produced in chem ica l reactions. When tem peratures a re h i g h , mo le­ cu les may brea k down i nto atoms or atom g rou ps. With slow cool i n g these may join together, i n reg u l a r order, to form c rysta ls. Most m i n e ra l s are c rysta l l i ne, being formed from coo l i n g m ixtures, liqu ids, or vapors i n the crust of the ea rth. The arrangement of a n otom's e l ectrons determines with what other elements it will combine, a n d i n what pro­ portions. The p hysica l cond itions i n molten materia l s a lso set the pattern by which chemica l elements form d iffer­ ent m i n era l s. The science of physica l chemistry has much to reve a l a bout how, w hy, a n d when m i nerals form.

14

I NT E R F E R E N C E PATT E R N S a re shown by this thin section of a rack rich in pyroxene, here viewed t h rough a polarizing microscope.

BIAX I A L

1NT E R F E R E N C E

F I G·

forms when a thin sheet of m uscovite mica is exa m ined through a pola rizing microscope. URE

OPTICAL PROPERTIES of m inera l s a re used ma inly by

experts, but a mateurs should know a bout them because they a re fundamenta l in precise m inera l identification. O ptic a l identification is h i g h l y accurate and can be used with pa rtic les of microscopic size. X-rays sent through thin fra g ments or powders produce a pattern depend ent on the structure of the molecules and so a re an a i d to identification. Pieces of m inera ls or rocks are mounted on s l ides, then ground t i l l pa per th in. These thin sections are exa m ined th roug h ord inary and po l a rized l i g ht. The bending of l i g ht as it passes throug h the m inera ls g ives patterns that aid in identifi cation. Fragments of m inera l s c a n be i m mersed in transpa rent l iq u ids of d ifferent d en­ sity to measure their index of refraction. This is d i stinct for each m inera l and is related to its crysta l system ( p p. 16- 17) . Thus an expert can te l l if a diamond or emerald is rea l o r false without do ing any d a m a g e to the stone. I t is worth paying m o re attention t o these optica l properties as you become more experienced.

.!'I<...J.Lll�

A check on this d i a m o n d ' s i n dex of refraction shows that bottom is cemented glass.

• .

....... ..

_,, index 1.8

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CRYSTAL FORM is critica l in m inera l identification as

it reflects the structure of the very molecules of the m i n ­ era l . I t is a lso t h e most d i ffi c u l t chara cteristic t o u s e a n d o n e that req u i res the most ca refu l study. Yet crysta l s a re so magn ificent in their beauty a n d symmetry it is some­ times hard to bel ieve they are natura l . The study of how they are formed revea l s mathematica l relation s h i ps as a mazing a n d as bea utiful as the c rysta l s themse lves. PerCubic

(Isometric)

Sys­

tem includes c rystals in which

the three axes (common to five of six systems) a re of equal length a n d are at right a n g les to one another, a s i n a cube­ exa m p l es: galena, g a r n et, py­ rite, a n d h a l ite. Tetragonal System has two axes of eq u a l length and one u n eq u a l . All three axes a re at right a n g les to one a n other, as i n zircon, ruti le, a n d cassiterite. Z I RC O N

RUTILE

Hexagonal System has three equa l axes at 1 20° an­ g les a rra nged i n one plane and o n e more axis of a differ­ ent length at right a n g les to these, as in q u a rtz, beryl, cal­ c ite, tourma l ine, a n d c i n n abar.

16

QUA RTZ

CALC I T E

feet crysta l s a re rare, a n d some a re of g reat va l ue. How­ ever, a frag ment or a n im perfect crysta l w i l l yield basic data to the experienced m i n eralog ist. Sometimes c rysta ls develop i n c l usters, or as tw ins. They reve a l d istortions, i n c l usions, and other i nterru ptio ns in their development. A very simple out l i n e of the six systems of crysta ls is g iven o n these two pages as a bare i ntroduction to the science of crysta l lo g ra p hy: Orthorhombic

System

has crysta l s with three axes a l l a t right a n g l es, but a l l of dif­ ferent length. Exa m p l es: su lfu r, barite, celestite, sta urol ite, a n d o l ivine. SULFUR

Monoclinic System has three unequal axes, two of which a re n ot at right a n g les. The third makes a right a n g l e t o the p l a n e of the o t h e r two, as i n orthoclase, gypsu m , ·micas, a u g ite, epidote, a n d hornblende.

E P I DOTE

STAUROL I T E

AUGITE

Triclinic System has three u n eq u a l axes but none forms a right a n g l e with any other. Ex­ a m p l es: p l a g ioc la se fe ldspa rs, rhodon ite, a n d cha lca nth ite. AMAZONSTO N E

R H O D O NITE

A scratches B

Try to scratch A with· B

Try to scratch B w ith A

B does not scratch A

HARDNESS is used in a rou g h manner in mineral identi­ fication. The re a re much more precise ways of measuring hardness in i n d ustria l laboratories. Thoug h arb itra ry, Mohs' sca le of ten m i nera ls is useful: 1 . Talc 2. Gypsum 3. C a l cite 4. F l u orite 5 . Apatite

6. Orthoclase 7. Q u a rtz

8. Topaz 9. Coru n d u m 10. Diamond

Remem ber these ten by using the odd sentence "The Girls Can F l irt And Other Queer Things Can Do." Gypsum is harder than ta l c but not twice as hard; fl uorite is harder than ca l cite a n d less hard tha n a patite. If a n u n k nown wi l l scratch a l l t h e m i nerals in the sca l e u p t o 4 and i s scratched by a patite, its hardness is betwee n 4 and 5. C heck care­ f u l l y to be sure there is a d isti nct scratch. Don't test hard­ ness on the face of a va l u a b l e crysta l . For field use here are some other convenient sta n da rds of hard ness:

penny 3

steel file 6.5

A bala nce used

SPEC I F I C GRAVITY is the re lative weight of a m i n eral

com pared to the weight of a n equal v o l u m e of water. Since the weight of a n equa l vo l u m e of water is identica l with the m i n era l's loss in weight when weig hed in water, specific g ravity (Sp. Gr.) is q u ickly deter m i n e d . A coru n ­ d u m c rysta l weig h i n g 2 . 0 o z . d r y weig hs 1 .5 o z . w h e n suspen ded i n water. The l o s s ( 0 . 5 o z . ) divided into the d ry weig ht g ives a specific g ravity of 4.0. T h is may seem odd, beca use coru n d u m contains only a l u m i n u m {Sp. Gr. 2 .5) a n d oxyg en, a gas. lea rn to estimate s pecifi c g ravity and make you r own measu rements as an aid to identi­ fi catio n . Below are some average fi g u res. Borax Sulfur H a l ite Sti l bite Gypsum Serpentine Orthoclase Qua rtz C a lcite

1.7 2.0 2.1 2.2

2.3 2.5 2.6 2.7 2.7

Talc 2.8 Muscovite 2.8 3.0 Tremo lite 3.2 Apatite C rocidol ite 3.3 3.5 Topaz Rhodoch rosite 3.6 3.7 Stau rolite Siderite 3.9

Corundum Rutile Ba rite Zi rcon Z i n cite C a ssiterite Cinnabar U r a n i n ite Gold

4.0 4.2 4.5 4.7 5.5 7.0 8.0 9.5 19.3

(Sp. Gr. of some m i n e r a l s may vary a s much as 25 per cent from sped· men to spec i m e n . )

-

+ aluminum Sp. G r . 2.5

oxygen a gas

coru n d u m S p . G r . 4.0

19

Rhombohedral c leavage: calcite

Basa l cleavage: mica

C u bi c cleavage: galena

·

C LEAVAG E is the way some minera l s s p l it a l ong planes related to t h e molecu l a r structure of the m inera l a n d par­ a l l e l to poss i b le c rysta l faces: The perfection of c l eavage is described in five steps from poor (as in born ite) to fair, good, perfect, and e m i nent (as in m i cas). The types of c l eavage a re usua l l y described b.y the n u m ber and direc­ tion of c l eavage planes. Th ree exa m p les of cleavage a re shown a bove. Use c l eavage as a n aid in identifi catio n ­ t h o u g h y o u may at fi rst fi nd it difficu lt t o te l l the face of a c rysta l from a fresh, perfect c l eavage s u rface. Fracture is the breakage of a m i n e r a l s pecimen i n s o m e w a y other t h a n a long c l eavage p l a n es. N o t a l l min ­ era l s show good c l eavage; most show fracture. Fresh frac­ tures show the m i n er a l 's true color. Five to seven types of fracture a re recog n ized; three are shown below.

Conchoidal fractu re: obsi d i a n

20

U neven fracture: a rsenopyrite

E a rthy fractu re: clay

COLOR is the fi rst of th ree c h a rac­ teristics that have to do with the way a m i n era l l ooks. In most meta l ­ lic ores it is a safe c l ue in identifica­ tio n . But i n q u a rtz, coru n d u m , cal­ cite, fl u o rite, agate, ga rnet, tourma­ l i ne, a n d others it is often d u e to i m p urities a n d m a y vary greatly. So use c o l o r with caution and use o n ly the color of a freshly b roken s u rface. N ote the s u rface ta rnish o n some meta l l i c o res; it differs from the true col or, but can be used for identification a l so. Streak is the color of the pow­ d e red minera l best seen when the m i nera l is rubbed agai nst a streak p l ate of u n g lazed porcelain (the back of a tile is exce l l e nt). In m eta l ­ l i c ores the streak may d iffer from the color and so is worth noting. Luster d e pe n ds o n the absorp­ tion, reflection, o r refra ction of l ig ht by the surface of a m i n era l . It is often a n aid i n identification. About a dozen terms are used, m ost of w hi ch a re se lf-explanatory: adamantine ( b ri l l ia nt), l ike d ia­ mond; vitreous ( g lassy), like q ua rtz; a n d metallic ( l ike meta l), l i ke ga le­ n a . The prefix· sub- is used when the characteristic is less c l ear. Oth­ e r lusters to n ote: d u l l, earthy, s i l ky, g reasy, pea r l y, resinous.

TOURMAL I NE

C RYSTAL

CORUNDUM

U S I NG A STREAK PLATE LUSTER meta l l i c

resi n o u s

g l a ssy

liGHT WILLEMITE A N D CALC I TE

C OMMON OPAL

U LTRAVIOLET LIGHT is invisible. I ts waves are too short to be d etected by the eye. However, some m inerals, when exposed to this l ig ht, are "excited"-they absorb the u l tra­ vio let light and e m it longer light rays w h ic h we see as co lors. Minera l s which do this are fluorescent. If they con­ tinue to e m it light after the u ltravio let rays have been cut off, they are phosphorescent ( l ike the l u m i nous dial of a watc h). A q u a rtz l a m p is a fi n e source of u ltraviolet light of s h o rt (about 1 1 1 0,000 in.) wave l e n gth. A n arg on light g ives l o n g e r u ltraviolet rays. Not all m i nera ls fl u oresce when exposed to u ltravio l et l i g ht. U ra n i u m m i nera l s do; so does scheel ite, a n ore of tungsten , and other tungsten m i nera ls. Other minerals may fl uoresce because of im­ purities, and sti l l others fl uoresce when from one loca l ity a n d n ot when from a n other; this makes the search for fl u o rescent m inera ls exciti n g . A porta b l e q u a rtz l a m p can be used o n fi e l d trips. Beca use o f t h e i r bea uty, fluores­ cent m inera ls receive a good dea l of attention, but the serio us study of fl uorescence is a difficu l t one.

22

MAG N ETISM occurs in a few m in era ls. lodeston e (a form of mag ­ n etite) is a natura l magnet. An a l ­ n ico m a g n et wi l l attract b its o f mag­ n etite a n d pyrrhotite. A few man­ g a n ese, n ickel, a n d iron-tita n i u m ores become m a g n etic w h e n heated by a b lowp i p e . ELECTR I C A L PROPERTI ES of m i nera l s a re varied. Thin slabs of q u a rtz c rysta l control radio fre­ q ue ncies. C rysta ls of su lfur, topaz, and other m in era l s deve lop an e lec­ tric c harge w h e n rubbed. To urma­ line crysta ls, when h eated, deve l o p o p posite c h a rges at o p posite e n d s of the crysta l . H EAT may raise the tem perature o f a m i n e ra l t i l l it w i l l f u s e i n a b l ow­ pipe fl a m e . Use o n l y sma l l, thin s p l i nters. The seven-point sca le of fusi b i l ity, with exa m p les, is: 1. Stibnite fuses i n alcohol l a m p o r

ca n d l e fl a m e 2 . Chalcopyrite f u s e s e a s i l y i n blow3.

4. 5. 6. 7.

pipe fl a m e Almandite ·fuses less e a s i l y i n b l owpipe fl a m e Actinolite: thin e d g e s f u s e e a s i l y with blowpipe Orthoclase: t h i n edges fuse with d ifficulty E n stat i te: o n l y thinnest edges fuse with blowpipe Q uartz : n o fusing at a l l i n blowpipe fl a m e

(980°F)

• •

-

Heated tou r m a l i n e develops electric cha rges b l owpipe flame

(1475°F) ( 1920°F) ° (2 190 F)

forceps

° (2374 F) ° (2550 F)

chalcopyrite

(Over

2550°f\

23

G E I G E R C O U NTERS are not a tool for the amateur

mineralogist but have become well known because of their use in locating or checking deposits of uranium and thor­ ium. The Geiger tube is the heart of the counter. A wire down the center of the tube has a negative charge. How­ ever, no current flows, because of the gas that fills the tube. When the tube is exposed to radiation, some of the molecules of the gas are ionized. They develop an electric charge because of electrons knocked from them. The ion­ ized gas conducts electricity and there is a momentary flash of current through the tube. This is recorded on a counter or dial, or heard as a click in headphones. Cosmic rays from outer space also discharge the Geiger tube, and these must be considered when searching for ore. In order to get an effect, the ordinary Geiger counter must be held close to the ore. Hence it works best on out­ crops and other exposed rock. The richer the ore, the more numerous the discharges and clicks. The scintillom­ eter is another sensitive apparatus used to detect radio­ active materials.

24

MI N ERALS as natural inorganic chemicals can be iden­ tified by their chemical properties as well as by hardness, streak, or luster. Once a mineral is dissolved (often a dif· flcult task), other chemical solutions can be added to identify the elements in it. Chemists make constant use of these "wet" tests. Although prospectors working in iso­ lated places can frequently identify a mineral or rock by its physical properties, they also collect and bring material in for laboratory study. Laboratory tests often involve a blowpipe, a short metal tube for blowing air into a flame. In blowpipe analysis, a bit of the mineral to be tested is heated on a charcoal block. The colored coatings which form identify the ele­ ments present. The mineral may be powdered, also, and a touch of the powder absorbed in a drop of melted borax to give a bead test (p. 28). When mineral powder is brought into a flame, the flame color may be studied. Powdered minerals are also heated in closed or open tubes (p. 30). Mineral analysis calls for the basic materials listed be­ low-as well as for a working knowledge of chemistry. Books to help you are listed on p. 1 56. Blowpipe C h a rcoa l b l ocks Alcohol o r gas b u r n e r Test tubes Open tu bes Chemical forceps Plati n u m wire

Mortar a n d pestle Blue a n d g reen glass Hammer and s m a l l anvil litmus paper Borax pow d e r a n d other chem ica l s Magnet

25

OX I D I Z I NG FLAME

R E DUC I NG FLAME

Use blowpipe to send o o i r i nto flame, molding na rrow cone a bout 2 For reducing fl ame, hold

strea m of it i nto a i n . long. blowpipe

beh i n d flame and heat specimen at tip of i nterior b l u ish cone. For oxidizing fl a m e, hold blowpipe i n flame a n d heat specime n at tip.

BLOWPIPE TESTS make use of an a lcohol, gas, or

ca n d l e flam e. Moving the b l owpipe back and forth as shown a bove p rod uces a n oxidizing fl a m e (extra oxyge n c o m e s f r o m the air b lown i nto the flame) or a reducing fl a m e ( hot gases take oxygen from t h e specimen). The powdered specimen set i n a h o l low at o n e end of a char­ coa l block is heated in the flame u ntil c h a n ges occur. Sometimes a fi ne, colored coating (sub l i mate) forms; some­ times a bead of meta l is left behind or cha racteristic fumes are released. When a fl u x (iodide, bromide, or ch romate) is added to the powdered min eral, differently colored coati n g s form . These may be used to confirm the tests. I n some tests t h e m i n era l i s heated o n a block o f plaster in­ stead of a c harcoa l block. Fi nal ly, the b l owpipe can be used to heat a m inera l specimen directly, as i n d eterm in­ ing fusibil ity. A s l iver of the mineral is h e l d by forceps d i rectly in the fl a me, as shown o n p . 23.

Blowpipe test for zinc: heati n g ore on c h a rcoal with oxidizing flame.

SAM P L E BLOWP I P E T ESTS for

the meta l l i c e l e m e n t in the m inera l specimen: Anti m o n y forms a dense wh ite coating, b l uish at the fringe; it is volatile, but n ot as much as a rsenic, which forms a s i m i l a r coating and has a garlic odor. B i smuth m i nerals g ive a n ora n ge-ye l l ow coating, w h i c h be­ comes g reen ish-ye l low o n coo l i n g . A g r a y britt l e b utto n o f b is m uth a l so forms. When iodide fl ux is m ixed with the powdered m i n e ra l , the coating is ye l low w i t h a reddish border. Copper When oxides are h eated in the red uc i n g flame with a fl u x practica l ly no coating resu lts, but a redd ish ba l l of meta l l ic cop­ per remains. Blowpipe fl a m e is col­ ored b l ue-gree n . Lead m i nera ls h eated i n a re­ ducing fl a m e l eave beh i n d a g ray ba l l of m eta l l ic lead. The coating is yel lowish (da rker when hot) with a white or b l uish border. Z i n c m i n e r a l s g ive a sma l l coating c lose to the specimen-bright yel low w h e n hot ( p . 26), w h ite when cold. Add a d rop of coba lt n itrate s o l ution to the coating, reheat, a n d t h e coating w i l l t u r n g ree n . Use plaster b lock with iod ide fl ux.

A N T I MO N Y

B ISMUTH

LEAD

·Z I N C

27

B e a d in o x i d i z i n g fla m e .

B E AD T ESTS help identify metals when minerals are dis­ solved in a flux and heated. The flux is borax, heated in a loop of platinum wire till a clear glassy bead is formed. The hot borax bead is touched to a trace of the powdered mineral and is reheated in reducing and oxidizing flames. The color of the bead is noted when hot and when cold. All traces of a previous bead must be "washed" off the wire before a new test is made. Below are the colors in some common bead tests. OXIDIZING FLAME

Metal

Cold

Hot

Cold

colo rless g re e n

yellow g reen

b l ue

blue colo r l ess

colo rless green blue

Antimony

yellow

C h ro m i u m

yellow

Cob alt

blue g reen

blue green yellow I ro n violet-brown v i o l e t M a n g a nese colo rless M o l y b d e n u m yellow brown violet N ic k e l colo rless-w h ite colorless Tita n i u m colo rless y e l low T u n gsten y e l l ow-b rown yellow Ura n i u m

Co p p e r

Va n a d i u m Alter

M.

REDUCING FLAME

Hot

green

yellow

b rown

g reen colo r l ess b rown colo rless-g ray yellow-g ray

green col o rless brown colorless-gray

y el low g ree n b rown

b rown green g re e n

yellow

lim, B l o w p i p e A n a lysis a n d Tests for Com m o n Min e rals,

OX I D I Z I NG

R E D UC I N G

COPP E R I RO N U RA N I UM

28

HOT

COLD

HOT

COLD

7935.

/ SODIUM

STRONTIUM

COPPER

POTASSIUM

Strong yel low, i nvisible through coba l t g l a ss.

Strong, i n tense crimson-red flame.

Bl ue, with some green, dependi n g o n ore.

V i o l et, visible as red through coba l t g l ass.

FLAME T ESTS depend on the fact that small amounts of mineral introduced into a flame will color the flame, de­ pending on the metals it contains. Flame tests are fairly crude, but when such flames are viewed through a spec­ troscope, a highly accurate kind of chemical analysis is possible. The spectroscope and the X-ray are important tools in advanced work with minerals and are essential in working with small, rare specimens. To make simple flame tests, use a clean platinum or nichrome wire. The wire, dipped in strong hydrochloric acid, is held in the flame until no change in flame color is seen. The wire loop is touched to a bit of the powdered mineral, also moistened with acid, and then flamed. The flame may be viewed directly, or through a cobalt blue glass, which masks the yellow sodium color. The Merwin screen, made of two overlapping layers of colored plastic, is also used to view flame colors. 29

On co n tin ued h e a t i n g it forms a y e l low to re d d i s h-brown s u blimate in t h e co o l port of t h e t u b e .

LEAD ORE (ga l e n a ) t u r n s a lig h t co l o r a n d for m s a w h ite s u b l i mate

when h ea te d in on open t u b e .

TUBE T ESTS involve heating powdered minerals in closed and open tubes to see what sublimates form in the upper, cooler part of the tube, and to notice fumes and odors from the heated mineral. The closed tube is an ordinary pyrex test tube. Use only enough mineral to barely cover the bottom. Hold at a low angle in Bunsen burner flame and heat until mineral is red hot. Watch for fumes and sublimates. The open tube can be a piece of straight or bent glass tubing about six inches long. The powdered mineral is inserted about an inch from the lower end, and the specimen is heated while being held at a low angle. Do not tilt higher or the specimen will spill. Air circulates through the open tube and oxidizes the mineral powder. Sublimates form at the cool end. Use a test tube holder for these tests.

30

in matrix

M E TALLIC MIN E RALS The metals are the core of our civilization. Life as we know it would be impossible without them. Here are the minerals from which our most important metals are ob­ tained; they form an interesting group for collectors. COPPER n uggets were found by a ncient m a n . Later, cop­

per was smelted from its ores. Today it is essentia l for practica lly a l l things electrica l and for many othe r uses. Chi le, Peru, Cyprus, Africa, Ja pan, a n d Austra lia have large deposits. Our deposits are largely i n Michigan, Mon ta na, Ten nessee, a n d the Southwest. Copper occurs principa l ly in volca n i c rocks a n d in veins. Native capper (H. 2 . 5 to 3, Sp. Gr. 8.9) is hard to mine. The su lfides a n d carbonates described o n t h e n ext page a r e easier t o h a n d l e. Some malachite and azurite is c u t f o r ornaments and gems, a s is c hrysoco l la, a copper s ilicate. Cuprite (copper oxide}, a reddish brawn m inera l, resu lts from oxi­ dation of other copper m i nera l s Sulfides a re b lack, purple, and yel­ low. The oxide and n ative copper . . a re d u l l red; the carbonates, blue \ .T � ).. I and g•een. C•y•ta I• D'O '"'"·

��� ·.

·

·

•

31

C h alcocite (Cu 2 S) is a dark meta l l ic m i nera l . H. 2.5; Sp. Gr. 5.5; strea k, g ray to b lack. A n im­ porta nt ore, it is found with the other three minerals on this page. Usu a l l y occurs i n vein d eposits; crysta l s rare. Covellite ( C uS), fou n d with other copper su lfide ores, forms thin deep b l u e plates, usua l ly ta r n ished to purple or b lack. Not as com mon or as rich in co pper as cha lcocite. H . 1 . 5 to 2; Sp. Gr. 4.6; l u ster, meta l l ic. Occurs a s crysta l s or incrustations.

B u tte, Mont.

Beaver Co., U tah

32

Born ite (Cu5FeS4) is ca l l e d peacock ore because of i t s usua l ly shi ny, purple ta r n i s h . An im porta nt ore, fou n d i n veins o r scattered in i g n eous rock. Crysta l s rare. Bronze­ co lored when fresh . H . 3; Sp. Gr. 5; streak, b lack. May conta i n sma l l a m ounts o f g o l d a n d si lver. Ch alcopyrite (CuFeS2), the common coppe r ore, is a b rassy, a l m ost g o l de n m i n era l . May form crysta l s but is m o re often fou n d in massive form, i n m ost co pper m i n es. H . 3.5 to 4; Sp. Gr. 4.2; streak, greenish-b lack; very brittle.

Cuprite (Cu20) forms by weathering of other o res and so is more com m o n near the surface. Cubic crysta l s fa irly co m m o n . Also occurs as g ra i n s a n d irreg u l a r m asses. H . 3.5; Sp. Gr. 6; co lor, red dish-brown; streak, b row n i s h .

Seven Devils, Wash.

C h rysocol l a (CuSi03·2 H 2 0) i s fou n d i n veins a n d. masses with q ua rtz in most copper m i nes i n the Southwest. Its c h ief value is as a g e m when even -co lored and rich i n q ua rtz. Color varies, often b l u ish g ree n ; H . 2 to 4; Sp. Gr. 2 . C rysta l s a re rare. Malach ite a n d Azurite a re usua l ly fou n d together. Malachite (CuCo3·C u (O Hh), more com mon than azurite, is various sha des of g reen. Azurite (2CuC03·Cu(OHh), w h ich is b l ue, forms crysta ls m ore often . Both occur in sm ooth or i rreg ­ u l a r masses i n the u pper leve l s of m ines. Com pact, dee p-co lored stones a re cut a s orname nts. H . (for both) about 4; Sp. Gr. 3 .7 to 4. A Z U R I TE- Bisbee, Ariz.

cut a n d polished

Azurite a n d m a l a ch ite mixture

33

GALENA C RYSTALS

LEAD does occur as the n ative m eta l , but on ly rarely. The m ost i m porta nt source of lead is the minera l galena, lead sulfide (PbS). It has been known for centuries, and lead, sme lted easily from it, has a lso been used si nce a ncient times. G a l e n a is fo und i n veins, pockets, and repl acement de­ posits in carbonate rocks. It occurs with z i n c, co pper, a n d si lver, often conta i n i n g enoug h of the latter m eta l s t o make the ore d o u b l y va luable. About two-thirds o f U.S. p roduction comes from lead-zinc ores. Galena is a heavy, brittle, si lvery-gray m i n e ra l w h ich com m o n ly forms cubic crysta ls and has perfect cubic cleav­ age. Its crysta l s were used i n early ra dio sets. H . 2.5; Sp. Gr. 7.5; streak, lead-gray. America n d eposits are in southeast Misso uri, the Tri-State (Missouri-Ka nsas-Ok la­ h om a ) area, i n I l l i n ois and Wisconsin, a n d i n C o lorado, I d a ho, and Uta h with si lver ores. Europe, South A rr: erica , a n d Austra l i a have com mercia l deposits also.

cleavage p l a n es

A N G L E S I T E R E PLAC I N G GALE N A Tintic d istrict, Utah

leadvil le, C o l o . C ER U S S I T E I N E m b reevi l le, Tenn.

Over a dozen other lead m i n ­ era ls exist, but of this n u m b e r o n l y two h a v e m u c h i m porta n ce as ores. Both a re secon dary m inera ls de­ rived from g a lena by the slow action of a i r a n d water. Silver­ bearing g a lena is roasted to form lead oxide a n d su lfur d ioxide gas, then red uced with carbon . Zinc is a dded. The si lver a n d zinc rise and are skimmed off. The zinc is removed by distil lation. Cerussite (PbC03) forms large w hite or gray crysta ls, sometimes needle-like i n bund les. It a lso occurs a s mas­ sive deposits o r as loose, crysta l l in e crusts. H . 3 ; Sp. Gr. 6.5; adamantine o r s i l ky l u ster, w hite streak. Ang lesite (PbS04) is often found with ga lena, a s a w h ite or gray crust. H. 3, Sp. Gr. 6.4; streak, w h ite.

GOLD is neither the ra rest n o r the most v a l u a b l e meta l,

yet it is part of the ·fou n dation of trade a n d c o m m e rce, and has m a n y uses because of its meta l l i c properties. Ancients who fou n d native g o l d prized it, a n d gold, beau­ tiful and easi ly worked, is sti l l widely used i n jewe l ry. A soft m eta l (H. 2 .5), it is sometimes a l loyed with copper to h a rden it a n d m a ke it go further. Pure gold is 24 carats; hence 1 4 ca rat gold is 1 4/24 or about 60 per cent g o l d . Go l d is fou n d i n q ua rtz veins, sometimes w i t h pyrite. T h e g o l d may occur within t h e pyrite itse lf-giv i n g foo l 's g o l d a rea l v a l ue. Gold may occur i n metamorphic rock a n d occas io n a l l y i n sed iments where it h a s been redeposited. O n l y rare ly is visible gold found in g o l d ore. It usua l l y ca n not be seen at a l l. Some o f t h e com m e rcia l ores con­ tain only 0. 1 o u nce of gold for each ton of rock. Gold in q u a rtz with pyrite-C a l .

G O L D N U G G ET- C a l .

36

X i p e , Gad af S p r i n g a n c i e n t g o l d w o r k f r o m Mexico

As g o l d d eposits a re eroded, the h eavy gold (Sp. Gr. 1 9.3) is concentrated in strea m beds where g ra i n s, fla kes, and even n uggets may be fou n d by wa sh­ i n g away the lig hter sand i n a g o l d pan or a s l uice. From these p lacer deposits m i ne rs have gone o n to search for the orig i n a l veins o r " l odes." Here the gold may be found as flecks i n the q ua rtz and, rarely, a s octa hedra l crysta ls. Gold is m a l leab le; color pa le to golden yel low; meta l l ic l uster. It occurs as a compound with te l l u­ rium in such m i n erals as sylva n ite (Au,Ag)Te 2 a n d c a l averite, AuTe 2 • Go ld may a lso be recovered from other meta l l ic ores.

GOLD C RYSTAL

0.1 in.

G O L D O R E - lead, S . Oak.

NAT I V E S I LV E R

S I LVER sometimes occurs as native si lver in large twist­

ing, bra n c h i n g masses. Another i m portant source of silver is the sulfide (Ag 2 S)-argentite. I n addition, si lver, lead, su lfur, and antimony form a whole series of ra re, com­ p lex m i n e ra ls. Silver may be a va l u a b l e by-prod uct in smelti n g lead, zinc, and other meta l s. Argentite is m assive, or it may form cubic crysta ls. Found w ith lead, copper, and zinc m i nerals. Color si lvery when fresh, b lack to g ray when tarnished. H . 2.5; Sp. Gr. 7.3; luster, meta l l ic.

pure silver 1 000 fi ne

38

sterling sliver 925 fine

coin sliver 900 fi ne

C I N NABAR

crystal

M E R C U RY, in the form of cinnabar (HgS), is freq uently

a bright red, attractive m i n e ra l fo und near hot springs and in low-tem perature veins-typica l ly near volca n ic rocks. American d eposits, concentrated in the Sierra Ne­ vada and coast ran ges, are more l i m ited than th ose of Spain. C i n n a b a r forms hexagona l crysta l s but is usua l ly massive or occurs as scattered fl ecks. H. 2 . 5 ; Sp. Gr. 8. 1 ; color varies from b lack to bright red; prism atic c l eavage. Mercury is a lso fou n d as silvery g lo b u l es of n ative mercury in deposits of c i n n a bar. It is used i n m e d i c i ne, in the m a n ufacture of thermom eters a n d explosives, a n d i n sev­ era l chem ica l i n d u stries.

I ro n floats I n mercury S p . Gr. 1 3.6

At room tem­ perature m e rcu ry is a liquid

mercury freezes

IRON ORES

M E TEORITES

a re " s h o o t i n g stars" w h i c h reach t h e earth . Same are stony; some a r e i ro n a l loyed with nickel and traces of other meta ls. Meteors ra nge from s a n d-gra i n size t o m asses wei g h i n g tons. S u r­ face ofte n pitted, oxidized, or ru sty. I ro n meteors a re mag netic. H. 4 to 5; Sp. Gr. 7.5.

( F e 3 0 4 ) is t h e only b l a c k ore t h a t con be p i cked u p e a s i l y by a mag net. The h a rd ( H . 6) a n d h eavy (Sp. G r . 5 . 2 ) black crysta l s o r ma sses are found i n b a s i c i g n e o u s rocks a n d metamor­ p h osed sedimenta ry rocks. A val­ uable ore, though sometimes d if­ fi c u l t to m i n e . Stre a k : black.

( F e 2 0 3 ) , the most im­ porta n t iron o re, conta i n s about 70 per cent iron. G reat beds oc­ c u r i n M i n nesota, Mich i g a n , Wis­ co n s i n , and a d j a cent C a n a d a . H e m atite varies from a r e d earthy powder to a d a rk, compact, s h i n y m i n e ra l . H . 1 to 6; Sp. Gr. a b o u t 5; strea k, c h e r r y r e d .

LIMONIT E , a n

HEMAT I T E

MAG N ETITE

iron ore with water ( 2 F e 2 0 3 · 3 H 2 0 ) . is soft a n d earthy (ye l l o w och re) o r i n compa ct, smooth, d a rk, rounded mosses. Never crysta l l i n e. Limonite with about 60 per cent iron fo rms a series of very s i m i l a r iron m i n er­ a l s. H . 1 to 5.5; Sp. Gr. a bout 3.5; strea k, yell ow-brown .

MARCAS I TE

{ F e 5 2 ) . sometimes called wh ite pyrites, is s i m i l a r but l i g hter and more brittle than true pyrites. I t occ u rs in radiating a n d coxcom b forms, a s crustatio ns a n d concretions, i n clays, peat, a n d coal . H . 6; S p . G r . 4 . 8 ; crysta ls commo n . Speci m e n s crumble and break u p o n sta n d i n g .

( Fe52 ) o r foo l ' s gold is not l i k e gold a t a l l , but w h e n tar­ nished may rese m b l e c h a l copyrite (p. 32). Used to obtain s u l f u r a n d sometimes a s a sou rce of i r o n . C rysta l s a re com m o n ; a l so occu rs as grains or in masses. H. 6; Sp. Gr. about 5 ; strea k, g reenish­ black; color, light bra ssy y e l low.

( F eS) v a r i e s i n com­ position b u t a lways conta i n s an excess of sulfur. Ofte n fo u n d with nickel (Pentlandite) and mined for its nickel content. Occurs as crys· ta l s, thin p l a tes, g rains, o r masses. Color, bronze (py rite is b rassy ) ; H . 4; Sp. Gr. 4.6; streak, g ray­ black. Often mag netic.

SIDERITE

PYRRHOTITE

PYRITE

(FeC03) is occasi o n a l l y u s e d as i r o n o r e b u t deposits are u s u a l ly sma l l a n d iron conte nt is low-48 per cent. C rysta ls com­ mon; more ofte n in masses w h i c h cleave like c a l c i t e ( p . 64) . Color, yellow, gray, d a r k brow n ; H. about 4; Sp. Gr. 3.8; streak, wh ite; luster, pearly.

41

ore

scrap

BLAST F U R NAC E

l i m estone

coke

air b last

p ig iron

Iron has long been m a n 's m ost i m porta nt meta l . Conti nuously op­ eratin g b l ast furnaces similar to the one shown are used to produce pig iron and ferro-a l l oys. The furn ace is lined with fi re brick not bound with m orta r. Iron ore is genera l l y a n oxide, as hematite, l i m o n ite, or magnetite, a lthough occasio n a l ly a su lfide is used after conversion to an oxide by roasting. The ore is d u m ped into the furnace a l o n g with coke, a n d l imesto ne f o r fl ux. B l a sts o f h o t a i r r o a r in f r o m the sides, u n iting with the carbon of the coke to red uce the ore to meta l lic iron which fl ows to the bottom of the furnace, be­ n eath the slag. The furnaces a re ta pped regu­ larly. Most of the m o lten iron is taken di rectly to Bessemer o r o pen hearth converters to be made into stee l . Some is run into mol ds, mak­ ing pig iron. O p e n - p i t m i n i n g , Mesa bi Range.

bar m a g n et

C a n a d i a n n ickel

N I C K EL ore, h a rd to smelt in the early days of European m i n ing, was thought bewitched and was spurned by m i n ­ e r s . Canada, w i t h the la rgest deposits l ocated near Sud­ bury, Ontario, produces about three fourths of the free world's nicke l . Niccol ite ( N iAs) and m i l lerite ( N iS) are m ino r nickel ores occurring with sulfide and a rsenic ores of coba lt and i ro n . The pri ncipal ore of n ickel (pentlandite) occurs in pyrrhotite (p. 4 1 ) and i s similar to it. Greenish secondary ores are found near the surface, w h ere weath­ ering has a ltered the primary minera ls. Oregon and Mis­ souri mines produce nicke l ores i n the U . S. N ickel, a mag n etic m eta l, is widely used in a l loys, especi a l ly with iron. Perma l l oy and a l n ico, both nickel a l l oys, are used in making m a g n ets. German s i lver, another a l l oy, i s used for kitchenware, ornaments, and e lectrica l heating wire. U.S. nickels (5-cent pieces) conta i n about 75 per cent copper and are n ot magnetic. Canad ian nickels, with a higher n ickel content, a re magnetic.

M I L L E R I T E IN CALC I T E St. Lou is, Mo. C o ba l t, Ontario

43

C O BALT is chemically related to

near Salmon, Idaho

I

0.1 in.

C RYSTAL F O R M S : c u b i c

0. 1 in.

1 2-sided

S k u t t e r u d , N o rw a y

nickel and iron, and its ores are often found with nickel and iron minerals. The Belgian Congo and Northern Rhodesia are the largest producers; there, the cobalt is found with copper. There are also large deposits of cobalt ores in the Scandinavian countries, and in Canada with nickel. Cobaltite (CoAsS) and skutteru­ dite (CoNiFe)As3 (about the same as smaltite) are the chief ores at Cobalt, Ontario. Both crystallize in the cubic system and look alike. Cobaltite has a hardness of 5.5; color, silvery-metallic. Skutterudite, which is similar, also contains vari­ able amounts of nickel and iron and is classified as an ore of which­ ever metal is dominant. Cobalt is a heavy metal (Sp. Gr: 8.9) used in hardening steels and in other alloys. Carboloy, an alloy of cobalt and tungsten carbide, is used in cutting steel. Another ferro­ cobalt alloy makes permanent magnets. Cobalt oxides are impor­ tant pigments in paints and cera­ mics, in which they are used to produce shades of green, blue, yel­ low, and red. It is the source of color in blue glass. Cobalt also has other chem ical uses.

T I N is seen daily as the thinner­ than-paper coating on the surface of tin cans. This layer protects the iron of the can from rusting. About half the supply of tin goes into the 50 billion tin cans made yearly. Tin is also an important constituent of bearing alloys ( Babbitt metal) and of type metal and solder. In its oldest use, and still a major one, it is alloyed with copper and some zinc to make bronze. Tin is essentially a one-ore metal. The ore, cassiterite (Sn0 2), tin ox­ ide, contains almost 80 per cent tin. It is commonly brown or black, though occasionally red, gray, or yellow. Streak, pale; luster, glassy to adamantine. Cassiterite forms crystals, but occurs more often as fibrous masses (wood tin) or as crusts or veins in granite and peg­ matite rock. It may be distinguished from limonite by its high specific gravity (7.0). The Malay placer de­ posits of gravel and cassiterite peb­ bles are mined by huge dredges. Small amounts occur in placer deposits in Alaska, but most tin comes from Malaya and Bolivia. The Romans m ined tin from placer deposits in Cornwall, England.

CASSITERITE

C A SS I T E R I T E-WOOD T I N

G u a n a j u a ta, Mexico

t i n ca n

type m e t a l

so l d e r

bearings

45

crysta l 0.2 i n .

in calcite Franklin, N.J.

Z I N C was used as a n a l l oy with copper to produce brass

long before it was know n as a meta l lic e l e ment. Now zinc is widely used i n coating iron to prevent rust (galva­ n ized i ron), as wel l as in dry-ce l l batteries, p a ints, other a l loys and i n chemical industries. Zinc ores occu r with lead and copper ores in veins associated w ith i g n eous rocks (p. 1 09) and as replacement deposits in carbonate rocks. Sph aler ite, zincblende, o r b lackjack (ZnS) is the primary m i n e ra l . Color: yel low, brown, o r b lack; l uster: resinous. H . 3.5-4. Sp. Gr. 4. Spha le rite has perfect c leav­ age and b reaks easily. Some specimens are fl uorescent; others emit flashes of l ight when scratched i n a dark room . 46

S M I T H SO N I T E O N G A L E N A Leadville, C o l o . Broken Hill, New South Wales H EM I MO R P H I T E

W I LLEMITE Franklin, N.J.

Zi ncite is ora n g e- red zinc oxide (ZnO), a n ore a t F ra n k l i n F u r n a ce, N . J . Found w i t h fra n k l i n ite, a m i n era l sim i l a r to m a g n etite, conta i n i n g zinc a n d m a n g a n ese. S m ithso n i te (ZnC03) fo rms a s zinc ores weather. It is often a crysta l l i n e crust but mostly earthy and d u l l . Good speci m e n s a re found i n t h e Southwest. H e m i morph ite (Zn4Si 2 0 , (0 H k H 20), a z i n c s i l icate w i t h water, forms crysta l s or earthy de posits. W i l l e m ite (Zn 2 Si04), tra n s l u­ cent, va ries i n color. Often fl uo­ rescent (p. 2 2 ) .

Tessien, Switze r l a n d

h a r d n ess

5

l vigtut a rea, Gree n l a n d

ALUM I N UM K ya n i te, or cya nite (AI2 Si05), is usua l l y found in sc h ists a n d g n eisses. The w h ite to b l ue-g ray or b l ack crysta ls a re long and b lade­ l ike. Luster, g lassy to pea rly; Sp. Gr. 3.6; hard­ ness u n usua l -4. to 5 a l o n g the crysta l axis, but 7 across. Cryo l ite ( N a 3AIF6) is a rare mi nera l . Sma l l amou nts have been found in Colo­ rado, but it is the o n e g reat de posit i n Gree n l a n d that was crucia l i n the h istory of a l u mi n u m, m a k i n g the smelting of ba uxite possi­ ble. Now, a rtifi c i a l cryo l ite is used. H. 2.5; Sp. Gr. 3; g lassy or greasy l uster. S p l i n­ ters fuse in c a n d l e flame. Corundum (AI 2 0 3 ) is a primary a l u m i n u m m inera l found in meta morphosed l i m esto nes and i n sch ists. Hexagona l crysta l s com­ mon. Coru n d u m a lso occurs as dark g ra n u l es with mag­ n etite - a form k n ow n as e mery and used as a n abrasive. H . 9-harder t h a n a n y other c o m m o n m in e ra l ; Sp. G r . 4 ; color varia b l e .

M I NERALS Bauxite, the ore of a l u m i n u m, is a g roup of re­ lated oxi des with water of hydrati on. Most abund­ ant i n warmer areas, it forms as a l u m i n um-bearing rocks are weathered. Color, w hite-though often sta i n ed brown or red by iron oxi des. H ., vari a b l e, 1 to 3; Sp. Gr., 2.5. Named after the region near Baux in F ra n ce where it occurs, Bauxite is fou nd i n Arka nsas (main U.S. de­ posit) and in a belt from Alabama i nto Georgia. The Guianas have rich d eposits. Kao l in, a group of at least th ree m i nera ls, a l l a l u ­ m i n u m s i l icates w i t h water (H4AI 2 Si209), is w h ite a n d sca ly when p u re. More of­ ten found i m p u re as clay; then it is earthy and col­ o red by i m p u rities. Kao l i n is widespread, t h o u g h pure d e posits are l i m ited. It is essentia l i n ceramics a n d has many o t h e r uses. It i s a lso a potenti a l sou rce of meta l lic a l u m i n u m , though com mercia l s m e lting meth­ ods a re yet to b e deve loped . C RYSTA L L I N E KAOL I N ( hig h ly m a g nified)

49

+

+

y ields 2 lbs. of a l u m i n a

3,4 l b .

of carbon

10 k i lowatt hrs. current

A L UM I N UM, as a commercia l meta l , has been known

for over a h u n d red yea rs, but its wide use has been much m ore rece nt. C lays conta i n i n g a l u m i n u m were used in making pottery long before meta ls were k n ow n . Pottery a n d other cera m ic products sti l l uti l ize large qua ntities of a l u m i n u m m i n era ls (p. 1 50). A l u m i n u m is a constituent of fe lds pars, m icas, garnets, corund u m , and c ryo l ite, but on ly the latter has ever been a n a l u m i n u m ore. A l u m i n u m o res are usua l l y seco nda ry-weathered a n d a l tered prod­ ucts of these m i nerals. A l u m i n u m , making u p over 8 per cent of the earth's crust, is more a b u n dant than iron, but worka b l e deposits are l i m ited . Bauxite, consisti ng of hyd rated oxides of a l u m i n u m , is the principal ore. In p rocessi ng, the 50 to 70 per cent a l u m i n u m oxide, c a l led a l u m i na, is fi rst ex­ tracted, then d isso lved in h uge vats of m o lten cryo l ite. A l u m i n a is red uced to m eta l l ic a l u m i n u m by carbon e l ec­ trodes carrying a strong e l ectric cu rrent. It co l l ects at the botto m of the vat. About a m i l l ion tons a year are pro­ d uced, m a i n l y for the transportation a n d construction i n d ustries. Pouring molten aluminum

C H RO M I T E - La n c a ster, P o .

C RO C O I T E - n e a r D u n d a s , Tasm a n ia

C H ROMI UM, a bright silvery metal, has become famil ­ iar in the flashy trim on automobiles and household wares. It is often used over a nicke l undercoat as a non-rusting plating on iron and stee l. Chromium has only one ore, though it occurs in about a dozen minerals. C h r o m ite (FeCr 2 0 4 ), the chromium ore, occurs widely, but workable deposits in the United States are limited largely to California and Oregon. Commercial deposits occur a lso in Africa, the Philippines, Turkey, and New Caledonia. Chromite occurs in basic igneous rocks or in metamorphic rocks formed from them. Chromite ( H . 5 . 5 ; Sp. Gr. 4.7) i s metallic black o r brownish; streak, dark brown. Sometimes slightly magnetic because of its iron content, it occurs in veins or in widespread granular masses, frequently with a coating of serpentine. C rocoite (PbCr04 ), a rare but handsome minera l, is formed when chrome chemicals encounter lead. Attrac­ tive crystals of lead chromate then develop.

51

MANGANESE is widely found, often with iron, barium,

cobalt, and zinc. The most common ores are secondary, formed by the action of air and water on manganese sil­ icates and carbonates. Deposits are common i n bogs and lakes. Manganese is used to toughen steel for machinery, rails, and armaments. Russia, India, South Africa, and Brazil have most of the ores. U.S. deposits are in Tennes­ see, Virginia, Arkansas, Arizona, and Montana. R h o d o n ite (MnSi0 3 ) -pink, yellow, or brownish-is best known from Franklin Furnace, N.J. H. 5 . 5 to 6.5; Sp. Gr. 3.5; translucent; streak, white. Large, flattened crystals quite common. Prismatic cleavage. R h o doch rosite (MnC0 3 ), softer than rhodonite (H. 4), rarely forms large crystals. Translucent with glassy luster; color pinkish, as in rhodonite. Massive, in veins or as crusts. Typical calcite cleavage (rhombohedral ). Psi l o m e l a n e (Mn0 2 · H20) appears often with barium and iron. Soft, dull, noncrystalline (see manganite, be­ low), but may form hard (H. 5) rounded or stringy masses. Soft, impure mixtures are called wad. M a n g a n i t e , MnO(OH), is often in prismatic crystals or fibrous masses. H. 4; Sp. Gr. 4. 3 ; streak, red-brown. Pyro lusite (Mn0 2 ), principal manganese ore, is earthy, powdery, granular, or fibrous. Hardness varies from 1 or 2 up to 6 in rare crystal s. Sp. Gr. 5; streak, b l ack. Forms fernlike crusts (dendrites) along cracks or as inclusions in moss agate. These are not fossi ls. MOSS AGAT ES

52

Pyro l u site d e n d ri tes in q uartz

C a l ifornia

R H O D O N I T E - F ro n k l i n , N . J .

P S I LOM E LA N E New Mexico

R H O DOC H RO S I T E B u tte, Mont.

MANGA N I T E I lfe ld , H a rz, G e r m a n y

PYROLU S I T E I ronwood, M i c h . PYROL U S I T E D E N D R I T ES on dolomite-Pri n ceton, I owa

53

U R A N I U M (discovered in 1 7 89 and isolated as an ele­ ment about 1 8 42) is now prized as a source of atomic energy. It occurs in some 50 minerals, most of them rare. The main ores are uraninite and secondary miner­ als formed from it by weathering. Actually, uranium min­ erals are widespread in granites and pegmatites. Speci­ mens may be collected wherever these igneous rocks are exposed. Commercial deposits are another matter. Ura­ nium prospecting requires time, patience, and skills which few amateur mineralogists possess. Ur a n i n ite (U0 2 ) i s steel black, opaque, hard ( H . 5 . 5 ) , and heavy; R a d i a ti o n s d isclose u ra n i u m . Sp. Gr. 9 to 9 . 5 for pure specimens. Streak from gray to brown to black; crystals rare. More common is p i tc h b l e n de, a form of uraninite which occurs in massive, fibrous or rounded masses.

URANOPHANE­

North C a r o l i n a

C A R N OT I T E ­

thwest Colorado

Uraninite alters to an orange or red gummy, waxy mineral of variable composition, called gummite. Carnot i te (K 2 ( U 0 2)2 (VO. k 3 H 2 0) is a complex min­ eral with vanadium and uranium. It occurs in weathered sedimentary rocks as streaks or earthy yellow grains. Common in the Southwest, sometimes on petrified wood. U r a n o p h a n e (Ca U 2 Si20 1 1 ·7H20) is found with uran­ inite as clusters of tiny yellow, needle-like crystals. It is widely distributed, but never common. Autu n ite ( Ca( U 0 2 )2 ( PO • k 1 0- 1 2 H 20) is another secondary uranium mineral. Note the greenish, pearly flecks. Autunite is common in small U r a n i u m occurrences amounts. This and most other uran i u m minerals fluoresce strongly under ultraviolet light. Radiation from these minerals can also be detected by the use of a Geiger counter or a scintillometer.

55

IMPORT ANT M I N O R M ETALS

l u n a C o u nty, N . Mex.

SC H E E L I T E

Visa lia, C a l .

VANAD I N ITE T u cs o n 1 A r i z .

M O l YB D E N I T E

56

C l imax, Colo.

Wolfram ite (Fe,Mn) W04 is a m i nera l of q ua rtz veins a n d peg­ matites. It is fou n d i n the form of ta bular or prism atic crysta ls; dark brown or b lack with submeta l l i c luster; H . 5 . 5 ; Sp. G r . 7 . 5 ; brittle. An ore of tu n g sten (wo lfra m)­ important i n lamp fi la m ents a n d in stee l-al loy cutting too ls. Schee l i te (CaW04), a n other ore of tungste n . H. 5; Sp. Gr. 6. Glassy, someti mes tra nsparent; ·. -s treak, wh ite. Color va riable, but l i g h t. Found in q ua rtz veins or at contact of igneous rocks and l i m estone. It is the most i m porta nt U.S. tungsten ore. Va n a d i n ite (Pb 5 (V04 h C I ) is a n attractive, fairly widespread va nadium m i n e ra l , but not a n i m ­ po rta nt ore. H . 3; Sp. Gr. 7 . Va­ n a d i n ite is a seco n d a ry m i n era l of lead a reas. Carnotite (p. 55) is a better source of vanadium, used in a l loy steels. Molybdenite (Mo52 ) is a m i nera l fo u n d in pegmatites a n d veins. It is soft ( H . 1 .5), meta l lic and opaq ue; streak, b l ue-gray. Occurs as fl ecks, o r ta b u l a r crys­ t.a ls. Molybde n u m is essentia l in too l -steel a l loys.

C o l u m bite ( Fe,Mn ) C b 2 0 6 a n d tanta l ite (Fe,Mn)Ta 2 0 6 a re ores

of rare m eta ls. Actua l l y, they a re a series of oxides i n c l u d i n g i r o n a n d m a n g a n ese. T h e m i neral is c o l u m b ite w h e n the amount of columbium ( n iobi u m ) is h i g h , and ta ntal ite w h e n it has more ta nta­ lum, w h ich is used as a n a l l oy in surg ica l i n struments. C o l u m b i u m a l l oys are u s e d i n rocket e n g i n es. The minerals a re d a rk b rown or b l a ck, c rysta l l i n e (often twi n ned). H . 6; Sp. Gr. 5.5 to 8; usua l l y opaque with a s u bm eta l l ic l uster. They form in pegm atite, often with tin a n d tungsten m i nera ls. Beryl · (Be3A I 2 (Si03) 6 ) is an ore of beryl l i u m as we l l as a gem sto n e ( p p. 84-85). The meta l is used i n a l l oys of copper a n d i n atomic resea rch. It is a l most as light as m a g n esium. M o n a zite, H . 5; Sp. Gr. 5, is a com p l ex m i n e ra l conta i n i n g thorium a n d a n u m ber o f other "rare ea rth " m eta ls. It occurs as ye l low resinous grains or as la rger crysta ls i n pegm atite and i n cer­ ta i n sand deposits in southeastern U n ited States. An even g reater number of "rare e a rths" a re f o und i n sam arskite, which occurs rarely in peg m atites.

COLUM B I T E A N D TANTA L I T E B e d fo r d , N . Y .

B E RYL-Ge rmany

MONAZITE Yo r k t o w n , N . Y .

S A M A RS K I T E S p r u ce P i n e , N . C .

57

I l m e n ite, C u m b e r l a n d , R . I . R u t i l e , Yo r k C o . , Po.

Gem rutile (sy nthetic)

Tita n i u m a l loys u sed in rockets

T I TAN I U M is a meta l with a future a n d its m i nerals w i l l

be o f increasing im porta nce. Light weig ht a n d a h i g h m e l t i n g p o i n t g ive it i m porta nce in rocket construction. Now used i n steel a l loys, as a c utti n g too l (tita n i u m car­ bide), and in w h ite po ints. Tita n iu m is abunda nt, making u p 0 . 6 per cent of the earth's crust. Its ores ore fou n d principa l ly i n southeastern U n ited States and Arka n sas, and in l n,dia, N o rway, France, Switzer l a n d , and Brazil. Ruti l e (Ti02) has varied fo rms. Most common ly it is b lack, often in Iorge prismatic c rysta ls. H . 6; Sp. Gr. 4.2; Streak, l i ght brow n . Found in igneous and m eta morphic rocks. Needle-l ike c rysta ls o re fou n d as i n c l usions in r uti­ loted q u a rtz. Synthetic ruti l e is used i n rings. I l men ite (FeTi03) is the more co m m o n ore of tita n ium fo u n d in many mag netite deposits; associated with g n eisses and metamorphic rocks genera l ly. Found as thin sh eets, flecks, ta b u l a r crysta ls, g ro ins, or massive. Meta l l ic b l o c k i n color; opaque. Streak from b lack to redd ish­ brown. H . 5 to 6; Sp. Gr. 4.5. 58

MAG N ES I T E Steven s Co., Wash .

DOLOM I T E Mon roe C o . , N .Y.

cleavage fragment

MAG N E S I U M, l ig hter than a l u m i n u m , is the eighth m ost com mon element in the earth's crust. It h a s become a meta l of major i m po rta nce- its a l loys fi n d wide use i n a i r p l a n es, i n other sheet m eta l products, a n d i n casti ng. I ts two principa l o r es are m a g n esite a n d dolom ite. Mag­ nesium is a lso m a n ufactured from sea water-260,000 g a l l o n s y i e l d i n g one ton of the meta l . Th e magnesium c h loride is treated with l i m e from oyster s h e l ls. Then the magnesium is extracted by e l ectro lytic actio n . M a g n esite (Mg C03), usua l l y d u l l wh ite, massive o r g ra n u l a r, sometimes g l assy, ra rely occurs as crysta ls. H . 4; Sp. Gr. 3. large deposits i n Washi ngton and C a l ifo rnia. Dolom ite (MgCa(C03h) is described as a non m eta l lic m inera l ( p . 65), but recently it has come into use as a n ore of magnesium-just as the c lay m inerals may eventu a l l y become ores of a l u m i n u m . Three light meta ls-a l u m i n u m , magnesium, a n d l it h i u m-are of g rowing i m porta nce. S p i n e l , a m a g n esium-a l u m i n u m oxide, is a well-k nown gem m i neral ( p . 85) which is found mainly i n Cey l o n , Burma, and Thailand.

59

S T I B N I T E, (Sb 2 S3), fo u n d with py­

ST I B N I T E Shikoku, Jopon

rite, g a lena, a n d a rse n ic m i nerals, is t h e o n l y c o m m o n a ntimo n y o re. It is more typical of l ow-tempera­ ture veins. Stee l-gray, meta l lic; H. 2 ; Sp. Gr. 4.5. C rysta ls c o m m o n , ofte n fo u n d b e n t . A n t i m o n y is used i n type meta l , pewter, a n d other a l loys. Native a ntimony is a l so found as a m ineral-but rarely.

ARS E N I C is a semi-meta l used i n a l loys. Its po iso nous compo u n d s a re used in sprays a n d in secticides. R e a l g a r (AsS), the s i m p lest ore, forms i n l ow-tem per­ ' ature veins as crusts, g ra ins, fl ecks, o r massive deposits. C rysta l s a re rare. H. 2; Sp. Gr. 3.5; resinous l uster; color a n d streak both orange-red. Rea l g a r s l owly breaks down on exposure to l ight to form orpiment. O r p i m e n t (As2 S3), often found with rea lgar o r stib­ n ite, is usua l l y ma ssive, though sometimes s h eetl ike. C rys­ ta l s ra re. H. 1 .5; Sp. Gr. 3.5; perfect cleavage. S pec i mens becom e d u l l on exposu re to l ig ht. Arsen o pyrite (FeAsS) forms i n h i g h -tem perature veins and pegm atites. Occurs massive or a s crysta ls. Sil ­ ve ry, m eta l l ic; H. 6; Sp. Gr. 6. An ore of arsen ic.

60

ORPIMENT M a n hatta n , Nev.

A R S E NOPYR I T E

REALGAR M a n hatta n, N e·

N O N M E TA L L I C M I N ERA L S N O N M ET A L L I C M I N ERALS form a large group o f m i n ­ era l s wh ich conta i n no m eta l or are nat used for the m eta l s they conta i n . G e m s a n d rock-form i n g m i n e ra l s a re i n sep­ a rate sectio ns. Even a few meta l l ic m i n era l s (pp. 3 1 -60) belong i n the non meta l l ic group, for w h i l e they conta i n meta l s, t h e y a r e n o t ores. The non meta l l ic m i nera l s a r e of g reat i m p o rtance - for insu lation, as fi l lers, fi lters, a n d fl uxes, a n d i n t h e cera m i c a n d chemical i n d ustries. The world's m ost common m i n erals belong i n this group. S U L F U R (S) is a n o n meta l l ic m i n era l e lement found i n volca n ic rocks, a r o u n d hot sprin gs, a n d i n sed i m e ntary "domes" ( p . 1 45) with salt, gypsum, a n hyd rite, and lime­ stone. It is yel low (someti mes brown), waxy o r resi nous, weak and brittle. H . 1 . 5 to 2.5; Sp. Gr. 2 .0 . Sulf ur's l ow melting point ( 1 1 0- 1 2 0 ° C ) a i d s in m i n i n g it from u n der­ g r o u n d d e posits. Superheated water is p u m ped down large p i pes, melting the su lfur; compressed a i r then forces the m e l ted sulfur out. Sulfur is used i n pa permaking a n d as a source of su lfuric acid.

crysta l

G R AP H I T E is o n e of the world's softest m i nerals. D i a m o n d

is the h a rd est. Both a re c a r b o n (C) . Graph ite occurs i n i g n eous a n d meta m o r p h i c rocks-sch ists a n d marb les. I t may f o r m when h i g h tem perature vei ns cut coa l deposits, a n d an a rtificia l form is made in e lectric furna ces. Gra p h­ ite is ea rthy, or forms sca ly or fl a ky crysta ls w ith a meta l ­ l i c l uster, g reasy a n d flexible. H . 1 ; Sp. Gr. 2 . 0 . Com mer­ cia l de posits in this cou ntry a re l i m ited to three m i nes in Alabama, Texas, a n d Rhode Island; these ca n n ot com pete with the rich deposits of Korea, Ceylon, Mexico, a n d Mad­ agascar. Graphite is used for dry and wet lubrication a n d f o r electrica l a n d chem ica l purposes Its best-known u s e i s as "lead" i n lead penc i l s, w here i t is usua l l y m ixed with other m ateria ls to g ive various deg rees of hard n ess. Graph­ ite is a strateg ic m i nera l . I ts latest use is a s a moderator to slow down neutrons in atom ic p i l es. 62

CALC I T E

I C ELA N D S P A R

TWI N N E D C RYSTALS

I c e l a n d S p a r is a tra ns­ parent cal cite which has the o ptica l property of bend­ ing light two ways, making words a ppea r double.

Twinned C rysta l s of ca lcite, g rowing together a s shown above ( l eft) are very com m o n . This is a ty pi­ col specta c u l a r form.

Dogtooth S p a r , a com­ mon crysta l l i n e form, with crysta ls long a n d pointed. C rysta l s from J o p l i n , Mo., a re we l l known.

Sta lactites a n d Sta­ l a g m ites form i n caves by

dripping water. Cal cite a lso forms in thin sheets or d ra­ peries from the roof.

63

TRAV E RT I N E Death V a l l ey, C a l .

C A L C I T E S A N D C RYSTALS Badlands of South Dakota

CALC I T E (CaC0 3), m ost common a n d widespread of the

carbo nate m i n e ra l s, is interesting beca use of its many a n d varied crysta l forms. C a l c ite occurs i n a n u m ber of structu ra l forms a n d freq uently g rades into dolom ite ( p . 65). G reat masses of c a l cite occur i n l i m esto n es (pp. 1 261 27); sma l l crysta l masses a re present i n rock open ings, w h i l e rare, tra n s pa rent crysta l s occur as Ice l a n d spar, va l ued for use in ra nge fi n ders and pola riz i n g m icro­ scopes. C a l c ite also occurs as a vein m i neral in a l most a l l rocks. C rysta l s a re com m o n . H . 3; Sp. Gr. 2.7. C l eav­ age: perfect, rhombo hedra l . Most ca lcite is opaque, s l i g htly colored by im p u rities; yel low, ora n g e, brown, and g reen shades occur. Ca lc ite is often fl u orescent. Other Forms of C a l c ite

N a i l - head Spar: fl atte ned, rhombo hedral crysta ls, ofte n in c l usters. Travertine: a genera l term for massive, nonc rysta l l i n e calcite a s fo u n d in caves. Opaque, often colored . Tufa : porous, white trave rtine from spring de posits. C h a l k : w h ite, soft, compa ct she l l s of s m a l l sea a n ima ls. Ala baster: a solid, banded traverti n e used for ornam ents. See a lso gypsum (p. 66). O nyx: an a labaster, often clearer and more tra n s l ucent. Satin-spar: fi b rous, s i l ky fo r m . This name a l so a pp l ies to a form of gyps u m . Calcite bubbles i n hydroc h loric acid. 64

A RAG O N I T E C RYSTALS

P R E C I O U S C O RA L

A RAGO N I T E C RYSTAL

Sicily

Italy

C u m be r l a n d , E n g l a n d

ARAG O N I T E is chemica l ly the same as c a l c ite (CaC03)

but is less c o m m o n and crysta l l izes in the orth orhombic system . It is s l ig htly ha rder and heavier- H . 3 . 5 to 4; Sp . Gr. 2.9. Aragon ite does n ot cleave as d istinctly as ca l cite, a lthoug h it, too, b u b b les stro ng ly in d i l ute hydroc h l o r i c a cid. Aragon ite is usua l l y w h ite, g ray, o r crea m . The mothe r-of-pea r l l i n i n g of sea shells is aragonite. F l o s f e r r i is a bra n c h ing g rowth of p u re w h ite aragon ite i n m i nes a n d caves. C o r a l , fo rmed by pla nts a n d a n i m a l s in warm seas, is a lso a ragon ite. Precious coral is val ued for gem and orna me nta l use. DOLOM I T E (MgCa(C0 3 ) 2 ) occurs in large bedded de­ pos its a n d as veins i n other sed iments. There a re exte n ­ s i v e deposits i n the Austria n Tyrol -the D o l o m ite A l ps. Dolomite is both a rock a n d a m i n eral ( p . l 09). The best m i n e ra l specimens come from veins or l i mesto ne cavities, and i n c l u d e c rysta ls with cu rved faces. Dol om ite is harder than ca lcite (H. 3 . 5 to 5; Sp. Gr. 2 . 8), but sim i l a r i n crysta l form a n d cleavage. Rea cts slowly with hydroc h loric acid. Wh ite or varicolored. Widely d istrib uted . C R YST A L S M e x i co

65

GYPSUM is a comm o n m in era l . It

crysta l Tru m b u l l C o u nty, Oh io

is a sed imentary rock precipitated from evaporating sea water under dry o r arid conditions. Massive beds of gyps u m are found in over a dozen states and in Mariti m e Canada. When m i n ed, gypsum is the basis of a multi m i l lion-dollar in­ dustry producing paints, plaster, plasterboard, ti le, a n d other con­ struction materia ls. A sma l l amount of gypsum i n Portland cement keeps it from setting too fast. Gypsu m was known a n d used i n Europe for centuries. It was first burned in open fires, later in kilns. H eati n g gypsum drives out part of the water; the b u rned gypsum, ground to a wh ite powder, is known as plaster of Paris, as it was fi rst made near there. When m oistened, p laster of Paris a bsorbs water again a n d hardens as gypsum rock, so it is used in making plaster casts and in plastering a n d a s an ingre­ d ient of many prepared construc­ tion materials. Crushed gypsum is used i n agri­ cu lture, being added to the soil as "land plaster." It a ids the growth of peas and neutra l izes a l ka l ine soils. Over 8 m i l lion tons a re m i ned an­ nually in this cou ntry-about one­ third of the world production.

Gypsum is a color less or w h ite m inera l, sometimes tinted by iron o r other i m p u rities. It is ca lcium sul­ fate, with water (CaS04·2 H 2 0). H. 2, Sp. Gr. 2.3. Luster is pearly, g lassy-sometimes fi b rous. Streak, w hite. Its crysta ls have two c l eav­ age p l a n es-o n e perfect. Does not b u b b l e i n cold hydroc h loric acid, but w i l l d isso lve i n hot. Most gypsum occurs i n bedded deposits. A com pact m a ssive form known as a labaster (a name a l so a p p l ied to s i m i l a r- l ooking calcite) is c a rved for o r n a ments. C rysta l l i n e gypsum (se len ite) occurs i n caves and l i meston e cavities-a lso in c lays, sha les, and some san ds. C rysta l s may g row severa l feet long, and may be twi n ned or c u rved. A n h yd rite (CaS04) is chemi­ ca l ly similar to gypsum, but d oes not conta i n water. It is fo und in c rys­ ta l l i n e masses, though good c rysta l s are r a r e . Sometimes it is fi b rous, gran u l a r o r scaly. Color w hite to g ray; strea k, w h ite. Luster, g lassy o r pearly, often tra nsl ucent, rarely tra nsparent. H . 3 to 3 . 5 ; Sp. Gr. 2 .9. It is often found with gypsum, and may a lter to gypsum by ab­ sorb i n g water. A l so occurs i n s a l t b e d s a n d w i t h sulfur i n "domes."

MASSI VE GYPSUM Gra n d Rapids, Mich.

F I BROUS GYPSUM M a m moth C a ve, Ky.

c rystal

67

H A L I T E or common sa lt is so d i u m c h loride ( N a C I ) . It has been used since prehistoric days, a n d there is n o substitute for it in n utrition or i n i n d ustry. A l l h a l ite comes from the sea. layers of rock salt mark a reas where seas dried u p i n a n c i e n t t i m e s . I n many p l aces salt is sti l l m a d e by evap­ orating sea water i n shal low basins. H a l ite is colo rless when pure, but is usua l l y d isco lored some shade of ye l low, red, g ray, o r b row n . It is trans­ parent to tra n s l ucent, b rittle, and with exce l l ent c l eavage para l l e l to its crysta l faces. H . 2 to 2.5; S p . Gr. 2.3. It occurs i n g ra n u l ar, fi b rous, o r crysta l l i n e masses, easi ly recogn ized by the cubic crysta ls a n d by the m i n era l 's fa m i l iar taste . H a l ite is rarely pure. It occurs with other salts of calcium a n d magnesi u m . GLAUIER ITE, o

s u lfate o f sodium and calcium, occurs a r o u n d min­ eral &p ritigs a n d with other evap­ orltn. H. 2-'1 white to gray,

t a l ifomfa

fer I I zer, is iOc hu m n itrate ( N a N08). I t occu rs i n C h i l e a n d our Southw,..._ w ith msum, h a l ite, oncl g lauberite.

SALTPETER, o

Sa l t a n d Rel ated Minerals a re part of the " a l k a l i " whic h ma kes s o m e weste rn s o i l s d i ffi c u l t to u s e f o r a g r i ­ cu lture. T h e s e m i n e r a l s f o r m u n der sem i-arid t o a r i d c o n ­ d itions, often w i t h b o r a x ( p . 7 0 ) . H a l ite is m i ned by shaft m i n i n g or by p u m p i n g water into the deposit a n d later p u m p i n g out the brine. I n pu rification , potass i u m and mag­ nesium sa lts, bromine, and iodine a re obtained as by­ prod ucts. The h a l ite is rec rysta l l ized, beco m i n g very pure in the process. In addition to its use in food and as a pre­ servative, salt is essentia l i n chem ica l ind ustries, i n the rh a n ufacture of soda ash for g l ass prod ucts, a n d i n soa p m a k i n g a n d meta l l urgy. C h lorine f r o m s a l t i s used as a b leach a n d i n water purification.

69

"Twenty-m u l e tea m " h a u l ing borax- Death V a l ley, C a L

BO RAX, origina l ly obta ined from deposits of volca n ic origin, now comes mostly from brines a n d d ry lake beds where ground water has con centrated the borax. Used in making g lass and enamels a n d i n chemica l ind ustries. Borax, sodi u m borate with ten pa rts of water, occurs in a l ka l i l a kes or a s a crust o n the desert soil. O n ce h a u led i n twenty- m u l e tea m s f r o m the Death Va l ley reg i o n . W h ite to g ray; H. 2, Sp. Gr. 2 .7; g lassy. BORAX Kern ite is chem ica l l y simi­ Esmeral d a, Nev. l a r to borax but conta i n s o n ly four pa rts of water. It is often colorless and transparent. H. 2.5; Sp. Gr. 2.0. Strea k w h1te, l uster g lassy. Coleman ite is a calcium Kramer, Cal. bo rate with five parts of water. Prismatic crysta l s common. Col­ or, wh ite. H . 4 to 4.5; Sp. Gr. 2 . 3 . Streak, wh ite. luster, g lassy to d u l l . Often found in white, cha lky or hard, g lassy masses.

70

COLEMA N ITE southern C aliforn i a

1vage Jment­ ohedral

t w i n crysta l s

F L U O R I T E i n commercial q ua ntities occurs i n both sedi­ menta ry and ig neous rocks. Veins of fl uorite (Ca F 2 ) with quartz or calcite sometim es conta i n lead, cop per, and z i n c m i nera ls. We a re t h e world's l a rgest producer of fl uo r ite, most of it m i n e d i n I l l i n ois, Kentucky, Colorado, a n d N e w Mexico. F l uorite is used t o produce a fl u id slag i n steel­ making a n d i n smelting ores. It is used i n making h i g h -test gaso l i ne, F reon, a n d many other chem ica l products. F l u­ o rite is a most attractive m i n e r a l of varied colors-w h ite, b l ue, g reen, a n d vio let. Tra nsparent to tra n s l ucent. H . 4; Sp. Gr. 3.2. Streak, w h ite; g l a ssy l uster. Good octa hedra l c l eavage. C rysta ls and fine c l eavage frag­ ments make attractive spec i m ens for the c o l l ector. Often fl uorescent in u ltraviolet l i g ht.

71

B A R I T E or ba rytes (BaS04) is a su lfate of barium, a sil ­ very m eta l . It is placed with the n o n m eta l l ics because it is rare l y a so u rce of the m eta l a n d is widely used other­ wise. Ba rite occurs i n many ways, occasio n a l l y as l a rge tra nsparent or tra n s l ucent crysta ls; sometimes as crysta l­ l i n e vein fi l l i ngs, with fl uorite o r c a l cite, o r with meta l l ic ores. Large con cretions are fo u n d in South Da kota a n d sma l l e r rose-sha ped o n e s ("d esert roses") i n the sa nds of O k l a h o m a . Barite is a f a i r l y soft ( H . 2.5 to 3.5) but heavy ( S p . Gr. 4.5) m inera l , colorl ess to wh ite, ye l l ow, g ray, and brow n . Luster, g lassy, sometimes pear ly; strea k, w h ite. Some­ times g r a n u l a r o r earthy. Crysta ls a re com mon, often broad a n d thick. Barite is u s e d i n making l itho­ pone for pa int, a s an a id i n we l l d r i l l i ng, i n making g l a ss, a s a fi l ler i n g lossy paper, and i n cera mics.

72

MASS I V E A P AT I T E N o rway

A P A T I T E C RYSTALS i n ca l cite O nta rio, C a n a d a

APAT I T E g ets its odd name from the Greek word mea n ­

i n g " t o deceive" beca use i t s v a r i e d f o r m s a n d colors caused e a r ly m i nera log ists to confuse it with a ha lf-dozen other m inera ls. Apatite may be tra nsparent, tra n s l ucent, or opaq ue, with a color that varies from w h ite to b rown, g reen, ye l low, or vio let. Apatite occurs i n veins with q u a rtz, fe ldspa r, a n d iron ores. Hexago n a l crysta ls a re common, some s i m i l a r to gem m i n erals. Apatite is a p h os­ phate of c a l c i u m , usua l l y with some fl uorine (Ca 5 ( C I,F)­ (PO. ) J ) . H . 5 ; Sp. Gr. 3 . 2 ; l uster, g l assy; strea k, white. Outsta n d i n g commercial depos its a re present i n Ontario a n d Quebec, Canada. Phosp hate rock, used for ferti l izer, contains m i n e ra l s related to apatite. A thin chip of a patite will color a gas flame ora n g e ( 1 ) . When wet with su lfuric acid (caution!) it colors the fl a m e a pale b l u ish-g reen (2) due to l i berated phospho rus.

?

2

I 73

TALC may form when mag nesium

FOLIATED TALC St. lawrence C o u n ty, N . Y .

G RA N U LA R TALC St. lawrence C o u n ty, N.Y.

STEAT ITE

rich rocks a re a ltered, especia l l y by heated waters. Hence ta l c occurs as a secondary m i n era l with ser­ pentine (p. 1 07), ch lorite (p. 1 06), sch ists, and dolomite. It is fou n d i n irreg ular deposits i n metamorphic rocks. Ta lc has a variety of uses ra n g i n g from cosmetics (ta lcum powder) to fi l lers i n pai nt, i nsecti­ cides, rubber, and pa per. The use depends o n the form i n which the ta l c occurs-th is may be m assive, fi b rous, or soft. Soa pstone is rock usua l ly rich in ta lc. Steatite is a massive ta lc, usua l l y of high g rade. Ta l c is fre­ q uently sheetlike (fo l iated) or granu lar. As a m i nera l , it is one of the softest ( H . 1 to 1 .5), S p . Gr. 2 .7. Fol iated ta l c has good basa l c l eav­ age and breaks somewhat like m ica, thoug h the scales are not elastic. Tra nsl ucent to o paque; col­ or varies from w h ite to g reenish, yel low, or pink. Pure ta lc has a g reasy, soa py feel a n d w h e n pow­ dered acts as a l u b rica nt. Ta l c and soa pston e were known i n ancient times. Eskimos ca rved l a m ps and pots from it, as did the Mou n d Builders. The Egyptians, Babylonians, and C h inese a lso made use of it.

ASBESTOS is the n a m e g iven to

a group of m i nerals d ifferent i n origin but o f s i m i l a r a p pearance. Orig in a l ly the term was a p p l ied to fi brous m i n e ra l s closely related to a m p hibole (p. 1 00). Of the fi brous a m p h ibo les, crocidol ite o r blue asbestos is best known. Mounta i n leather is a heavy, matted f o r m ; its fibers a re usua l ly short a n d b rittle. The best-known source of asbes­ tos is a form of serpentine (p. 1 07) known as ch rysoti le. It is silky, fi brous, a n d stron g . Most c h rysoti l e comes f r o m the famous Quebec a n d Vermont deposits, where it hon ey­ combs the serpe ntine rock. Here the cross fi bers vary from Y:z to 3 inches in length. The long fibers are i n short supply and a re va l ued very h i g h ly. The U n ited States uses about 50 per cent of a l l asbestos produced; 90 per cent of this comes from Canada. C h rysotile frbers are so fi n e they can be d ivided into a l most invisible strands. They spin wel l a n d a re used in woven i n s u l ation a n d for fireproofi n g . The fi bers d o not burn a n d they cond uct heat very slowly. Shorter fi bers a re m ixed with gyp­ sum to make asbestos board. Sight identification of c h rysotile is easy­ n o other m i nera l is this fi b rous.

C ROC I DO L I T E ASB ESTOS

C H RYSOT I L E ASB ESTOS Q u ebec, C a n .

LONG-F I B E R E D C H RYSOT I L E Th etfo rd, Quebec, C a n .

common c rysta l forms

q u a rtz ra·d ia crystal

q u a rtz prism

silica crucible

QUARTZ is one of the most common m i n e r a l s i n t h e e a rth's crust. As the chem ica l s i l ica (Si02) it f o r m s a n i m p o rta nt p a rt o f most ig n eous rocks. Some san dstones are a l most 1 00 per cent q ua rtz, and so are such m eta­ morphic rocks as q u a rtzite. At d ifferent tem peratures q u a rtz c rysta l l izes i n d ifferent ways. For this reason its crystal structure is often an aid in determ i n i n g the tem­ perature conditions under w hi ch a rock formed, since o n e variety, a l pha-q ua rtz, c h a n g es to a n other, beta­ q ua rtz, at 573 ° C . Quartz occurs i n crysta l l i n e masses a n d , when condi­ tions permit, forms hexagonal c rysta l s ( p p . 78-79). Doubly term i nated qua rtz crysta ls (often fo u n d i n l i m estone cav­ ities) have such loca l n a mes as Herkimer d iamonds. larger c rysta l s a re found l i n i n g cavities; they a re often cut a s gem sto nes and are sold as rock c rysta l . Brazil is famous for its deposits of crysta l q u a rtz. Q u a rtz a lso oc­ c u rs in a form in which the c rysta ls a re of m ic roscopi c size a n d h e n c e not a p parent ( p p . 80-8 1 ) . Sil ica combined with water is opal (p. 82).

76

Qua rtz is sometimes colorl ess but more c o m m o n l y w h ite, sometimes ye l l ow, b rown, pink, green, b l u e, o r b l a c k . Its l u ster is g l a ssy in crysta l l i n e forms, waxy o r g reasy i n cha l cedony. H . 7; Sp. Gr. 2 .6; streak, w h ite; brittl e with conchoid a l fracture. Quartz is best recog n ized by its ha rdn ess, l uster, a n d occurrence, and by its crysta l form when evident. Ma ny kinds of q u a rtz a re valued as gems a n d are classed as sem i p recious sto nes. When c rysta l q ua rtz is cut at a n exact a n g l e to its axis, pressure o n it gen erates a m i n ute el ectrica l cha rge. This effect m a kes q u a rtz of g reat usef u l n ess i n rad io, television , a n d radar. T h e s u p p l y o f natural rad io q ua rtz is s o l i m ited that methods for g rowing q u a rtz crysta ls in the l a b o rato ry have been develo ped . Q u a rtz tra nsm its s h ort l i g h t waves (u ltravio let) better than g lass. When not of rad i o q u a l ity, c rysta l q u a rtz is m e lted to form b l a nks to make spec i a l lenses a n d prisms. Optica l q uartz can b e m a d e o n l y from c rysta ls. Less c l e a r q ua rtz is fused to m a ke l a b o ratory ware that is h i g h l y resista nt to chemica l actio n . Q u a rtz sand is used in m a k i n g g l ass. 77

Q U ARTZ is the m ost com m o n kind, though wel l -deve l o ped c l e a r crysta ls are rare. Rock crys­ ta l (colorless crysta l q u a rtz) makes a fi ne gem. The colors in crysta l q u a rtz may in part be d u e to i m purities ( m an­ g a n ese, iro n , n icke l ) or to radium a ctivity, a s i n smoky q ua rtz; some d isappear when the q u a rtz is h eated . The c rysta l s ofte n incl ude a i r b u b b l es a n d traces of othe r m i n era ls. Hairl ike crysta ls o f r u t i l e f o r m ruti lated q u a rtz o r sagenite. Cot's eye a n d tiger's eye may conta i n fi bers of asbestos. Ferrug i n o us q u a rtz is c o l ored by hematite.

C RYSTAL L I N E

occ u rs in c rystal­ line masses-ra rely as individ u a l crysta I s . S o m e rose q u a rtz is as­ teriated-that is, the cut stone re­ flects or transmits light i n a sta r­ l i ke pattern. The color is probably due to traces of manga nese. ROSE QUARTZ

color may b e due to traces of m a n g a n ese. Deeper col­ ored s P ecimens a re cut a s gems. Once h i g h ly prized, a methyst l ost much of its value after the g reat Bra z i l i a n deposits were fo u n d .

AMETHYST

QUARTZ, also called cairngorm o r Scotch topaz, varies i n color from smoky yellow to brown a n d black. The latter form is called marion. A well-known Scotch gem stone, though a l so fou n d a n d prized elsewhere.

SMOK Y

is an u ncommon variety, d ifferent from the violet amethyst. It is fou n d in the Blue Ridge Mountains, a n d with blue fe l d s p a r i n the Smokies. BLUE QUARTZ

is a y e l l ow q u a rtz a l so c a l l e d false topaz beca use of its color. Good crysta l s of gem q u a l ­ i t y c o m e from B r a z i l . N o t t o b e confused with p a l e smoky q u a rtz. CITRI N £

fo u n d in veins, is the most com m o n crysta l l i ne q u a rtz. I t is translucent to opaque a n d is n ot often used a s a gem.

MI LKY 'QUART Z ,

Q U A RTZ W I T H I NC l U S I O N S

tiger's eye

78

with rutile

with iron oxide

AMETHYST Brazil

ROSE QUARTZ South Da kota

S MOKY Q U A RTZ Scotla n d

B L U E . Q U A RTZ P e n n sy l va n ia

CA I R NGORM (MO R I O N )

C IT R I N E Q U A RTZ Brazil

M I LKY Q U A RTZ New H a m ps h i re

79

C RYPTOC RYSTALLI N E QUARTZ merely means q ua rtz

w ith h idden or m icroscopic crysta ls, in contrast to the va rieties described on the preced ing page. This group in­ c l udes the chalcedon ies and the fl i n ts, c herts, a n d jaspers. Most of these a re tra n s l ucent o r opaque; some a re color­ f u l a n d o re prized as gems. CHALCEDONY is a group term far a waxy, smooth form of q u a rtz often l i n i n g cavities, fi l l i n g cracks o r formi n g crusts. Sometimes transpa rent, u s u a l ly tra nsl ucent. C o l o rs from wh ite to g ray, bl ue, brown, o r black. CARNE L I AN (sard) is a clear cha lcedony, usually some shade of red o r reddish brown. JASPER is a n opaque q u a rtz usu­ a l ly red, yellow, o r brown, or a mixture of these colors. Sometimes b a n d e d . May grade into chert.

is a g ray, brown, or black q u a rtz freq uently fou n d a s nod­ u les i n c h a l k . D u l l e r, more opaque and rougher than chal­ cedony, it b reaks with co nchoidal fracture, produci ng sharp edges. Widely used by early m a n for m a k i n g tools. F LINT

80

Dover, E n g l a n d

CHR YSOPRASE is a transl ucent, app le-green chalcedony; coloring d u e to nickel oxide.

is chalcedony with a banded or irreg u l a r, variegated a p pearance. Bands may be wavy or para l le l , from d ifferences i n deposition. Petrified w o o d i s usu­ a l ly a n a gatized wood . Agate may be a rtificia lly colored. See p . 52 for moss ag ate. AGATE

i s a gate with even, par­ a l l e l bands usually of black a n d wh ite o r brown a n d w h ite.

ONYX

is a fo rm of onyx with a lternating bands of s a rd (ca r n e l i a n ) a n d w h i te-that is, of red a n d w h ite bands.

SARDONYX

CHERT, o r h or n sto ne, i s a n im­ p u re form of fl i nt- usually more brittle. Color: wh ite, y e l low, gray, o r brow n .

C H ERT- I l l i n o i s

C A R N E L I A N-Brazil

C H RYSOPRASE-Califo r n ia

ONYX-Brazil

BAN D E D AGATE-Mex ico

EYE AGATE-Brazil

C HALC EDONY-Tampa, F la.

JASPE R-MiCh i g a n

81

OPAL is a n oncrysta l line form of quartz - a sil ica gem conta ining varying amou nts of water (usua l ly 3 to 9 per cent). O pa l forms as a low-temperature d eposit around hot springs and in veins, as in Ne­ vada . It makes up the skeletons of diatoms and sil iceous sponges. O pa l is usua lly colorless or white, with color only in gem forms. H . 5.5 to 6.5; Sp. Gr. 2. 1 . luster g lassy, pea rly, or resinous. Streak wh ite. Among the varieties a re: Common Opal Milky white, g reen yel low to b rick red; some­ what tra nslucent, glassy, or resin­ ous. Widespread, often in volcanic rocks. Various names for d ifferent colors and gem forms (p. 86). Hyalite is a clear, colorless, g lassy opa l en crusting rocks or fi l l­ ing sma l l veins. Sometimes tra nslu­ cent or white. Geyserite or sil iceous sinter is a form of opa l found around gey­ sers and hot springs. It may be fi rm, porous, or fi brous; usua lly gray or white, a n d opaque. Often forms odd structures. Tripol ite is formed of m icro­ scopic shells of d iatoms (diatomite) and other organ isms. White, cha lky, fi n e-grained, but hard. Wil l scratch glass. ·

HYALITE Walbch, Bohemia

G EYSER I T E-Wyom i n g

�. •

D I ATOMS (magn ified)

>

82

-

T R I POLITE Ma-ch usetts

GEM M INE RA LS G EMS are the m ost p rized and famous of a l l mi neral s. A l l a re better, c lea rer, o r m o re c rysta l l i n e forms of m i n ­ era l s which in common occurren ces are less beautif u l a n d less specta c u l a r. D i a m o n ds, emera lds, rubies, a n d sap­ p h i res sta n d out as the true gems. Other stones a re c l a ssi­ fied as semiprecious and orna menta l sto nes. Scarcity and fashion a re i m porta nt i n dete r m i n i n g the va l u e of a g e m , but the fo l lowi n g p hysica l pro perties are prized : l u ster, tra n s pa rency, c o lor, a n d hardness. l uster depends o n how l i g h t is refl ected b y the m i n e ra l . T h e tra nsparent gems a lso refract or bend l i ght a n d a re cut to turn the light back into the observer's eye. C o l o r is essential i n some gems, and incidental i n others. It m a y a d d o r d etract g reatly f r o m the gem's va lue. T h e h a rd e r the gem, the better it resists scratching of i t s p o l ished s u r ­ faces. H e r e a re some of the best-known g e m s a n d semi­ precious sto nes. Many other m i nera l s and some rocks are occasion a l l y used a s gems.

b rown yellow are p u re carbon (C); 1 0; Sp. Gr. 3.5. F o u n d as iso· metric crystals or crysta l l i n e masses. Colorless o r with t i n ts of yellow, pink, b l ue, brown, a n d b lack. When not of g e m q u ality, diamonds have impor· tant i n d u strial uses a s a b rasives. D I AMON D S

H.

D I AMO N D IN MAT R I X South Africa

83

TRANSPARENT G EMS are striking fo r their l uster a n d

b r i l l i a n c e a n d often f o r hardness a n d c o l o r too. Most a r e oxides o f a l um i n um , bery l l i u m , a n d mag nesium, some­ times with s i l ica. All q u a rtz gems (pp. 86-87) are si l ica. is a l ig ht b l ue­ g reen fo rm of beryl (3BeO·AI,03• 6Si02), o n l y ore of t h e metal bery l l i u m . H . 7 .5 to 8 . It a lso oc­ curs as y e l lowish g o l d e n bery l . F o u n d i n many New E n g l a n d l o ­ cal ities.

AQUAMAR INE

CH RYSOBER Y L d iffers from beryl in being BeO•AI 203 . H a rd­ ness 8.5; Sp. Gr. 3 .6. Color: green, possibly d u e to chrom i u m . Alex­ a n d rite, a dark g reen form, is red by transmitted light.

C H RYSO BERYl-New Yor k is a form of beryl varying i n color from light to deep emerald green. Oriental emerald, a green coru n d u m gem, is harder a n d may be the most va l u a b l e gem. E M ERA L D

CORUNDUM M INERALS are a l l r a r e f o r m s of a l u mina (AI203). The gems va ry i n color. Deep red r u b ies a r e val u e d m o re than d ia ­ monds. Sta r s a p p h i res reflect light i n a six-pointed star, a s do a few other minerals. Green, p u r­ ple, a n d yellow coru n d u m a re known as o riental emerald, orien­ tal amethyst, and o r ienta l topaz.

STAR SAPP H I R E Tasmania

84

c u t sapphire

a m i n e ra l of g r a n ites and other igneous rocks, is a n a l u m ino-fl u o ro-sil icate. la rge crys­ ta l s have been fou n d , some of gem q u a l ity. These a re usually yellow, brown, o r p i n k (when heated ) . H . 8 ; S p . Gr. 3.5. False topaz is brownish q u a rtz. TOPAZ,

are a common group of sil icate m i n e r a l s ( p p . 1 04 - 1 0 5), sometimes of gem q u a l ity. Pyrope and a l m a n d ite a r e best known. Green dema ntoid is a l so a gem. GARNETS

( LiAISi206) occurs i n pegmatite rocks, often form­ ing long crystal�. Two g e m forms exist: H i d d e n ite, a g reen gem spod u m e n e from N orth C a r o l i n a , a n d k u n zite, p i n k colored, fi rst fou n d near San Di ego, C a l . Gem spodumenes a l so occur i n Brazil. SPODUMENE

PYROPE New Yo rk

DEMANTO I D N o rway

(ZrSi04) i s common in igneous rocks, b u t fairly rare as a gem sto n e. C l e a r brown crysta ls turn blue w h e n heated a n d hence m a k e better gems. Z IRCON

commo n l y black ( p . 95), fo rms l o n g crystals, some­ times varicolored. Red, g reen, b rown, a n d b l u e t o u r m a l i n es are known. TOURMALINE,

(MgAI204) someti mes reaches gem q u a l ity, the best red gems com i n g from C eylon. Brown, green, and even blue spinels oc­ cur. H . 8 ; Sp. Gr. 3.8.

TOURMAL I N E - B r a z i l

SPINE L

Cey l o n

Some transparent gems a re identica l m i n e r a l s that dif­ fer o n l y in co lo r, as the ruby a n d the sa p p h i re. Tra ns­ paren cy, lack of flaws, c o l o r, and size dete r m i n e the va l u e of these g e m s . For synthetic g e m s , see p p . 92-93. 85

Q U ARTZ G EMS, the best known semi precious stones,

are the same a s the m i nerals described on pp. 76-82. Of these gems, opa l s a re the m ost va l u a b le, some b e i n g c l as­ sified as precious. The tra nspa rent q u a rtz g e m s range from colorless through yel low, brown, b l ue, b l ack, purple,

C ITR I N E

AST E R I AT E D ROSE Q U A RTZ

SMOKY Q U A RTZ

AMET HYST

T H R E E C UTS OF ROC K Brazil

PREC I O U S OPAL Australia · ·

86

F I R E OPAL Mexico

BLAC K OPAL Austr a l i a

p i n k a n d , rarel y, green. The translucent or opaque q u a rtz gems have an even wider array of colors a n d forms. Some are banded, striped, o r mottled. Names of a l l these gems vary loca l ly. Some bea r several names; some names are used for severa l stones.

W H ITE C H ALC E D O N Y - U ruguay

AGAT E -Iowa

ONYX-Brazil

:�-��-,�/ 'k-�-��-�..

�

•

·�\o. '

'

\r '>

•

...

I

.

-

J A S P E R-Monta n a

C H RYSOPRASE-Col.

C A R N E L I A N - N . Mex.

87

Tibet

Australia

CARVED J A D E early C h i n ese

JADE is the n a m e given a group of opaque, waxy o r pearly m i n ­ erals, usually g r e e n but a l s o y e l ­ l ow, white, o r p i n k . There are two kinds of "true jade." One is jade-

ite, a gem form of pyroxene. The other i s neph rite, a form of am­ phibole (pp . 1 00- 1 0 1 ) . light, transl ucent, emerald g reen jade­ ite is considered a p reci o u s stone.

M OONSTONE

is a l bite (p. 99) with a b l u ish shee n .

AMAZON I T E

is a rock r i c h i n ! a z u rite. U s u a l l y a n ornamental stone, it i s a l so u sed a s a gem.

MALACH ITE,

LAP IS-LAZ U L I

i s a green form of gem-q u a l ity microcl i n e (p. 99).

often with a z u rite (pp. 32-33), occurs in m a sses. C u t fo r g e m s or o r n a m ents.

OPAQ U E G EMS, with the exception of jade, g rade off

into ornamenta l stones. The group incl udes representa­ tives of meta l l ic o res and rock-forming m i nerals. Some, l ike obsidian, lapis, and jet, are better classified as rocks. One u n usua l m i neral that could fit in t h is gr oup is the 88

R HODO N I T E may be used as a gem sto n e because of its color a n d h a r d ness. See also p p . 52-53.

softe r t h a n rhodonite, has the s a m e attractive p i n k color. See a l so pp. 52-53.

HEMATITE, an i ro n mineral (pp. 40-42), is cut a s a b lack, shiny gem w h e n crysta l l i n e .

JET, a tough form of soft coal, takes a high polish. A sem i p reci­ ous gem from E n g l a n d and S p a i n .

o r v o l c a n i c g lass ( p . 1 1 6) has l o n g been u s e d f o r a r­ rowheads a n d p r i mitive cutti n g tools. I t polishes w e l l a n d ma kes an attractive s e m i p recious stone.

a copper-a nd-a l u ­ minum phosphate m i n e r a l , is prized by weste rn I nd i a ns. Good q u a lity turquoise is rare. C h e a p sto nes a r e often dyed b l u e .

OBSI DIAN

R HODO C H ROSITE,

TURQUOISE,

pearl, formed by a number of fresh-water a n d m a r i n e m o l lusks w h e n sa n d o r some o t h e r m ater i a l irritates the a n i m a l 's mantle. layers of a ragonite form the pearl, w h i c h g rows year b y year. P e a r l s are soft ( H . 4), but h a v e a u n iq u e l u ster. 89

b a g uette

brilliant

emerald

GEM C U T T I N G is on a ncient a rt w h i c h has often been successf u l l y pursued by amate urs. With compa rative ly l ittl e equipment a person con cut and pol ish gems a n d ornamenta l stones a n d con l e a r n t o m o u n t them i n h a n d ­ m o d e o r purchased settings. As a creative, satisfying hob­ by, gem cutting g rows more p o p u l a r each yea r. Enth usiasts often form c l ubs for m utua l aid or do their work as one activity of a rock a n d m ineral c l u b . Ski l l i n cutting and polishing comes with practice. If one ca n n ot fi n d gems or semiprecious stones, rough materia l o r portly worked " b l a n ks" con be purchased from dea l ers by the piece or by the pou n d or ca rat, depending o n the sto ne. With a p p a ratus powered by a sma l l e l ectric motor, the a m ateur fi rst learns to cut stones a n d m a ke cabochons, Dop stick h o l d s gems for cutting ond polishing

90

s i m p l e gem cutti n g a n d polish i n g outfit

pieces with round o r cu rved s u rfaces. Later h e learns to cut stones with fa cets o r faces, which brings out the b r i l ­ l iance of tra nsparent gems. F ive common types of faceted c uts are shown a t the top of p . 90. As i n m ost other h obbies involving ski l l , one learns best by work i n g a n d studying with a person of experie nce. After you have begun, the books and magazines o n gems a n d gem cutting l isted below w i l l be of va l u e. POPU LAR G E M O LOGY, Richard M. Pearl. J o h n Wiley & Sons, I n c., New Yo rk, 1 94 8 . A n i ntroduction to gems by a n outsta n d i n g coll ecto r. T H E ART OF G E M C U TT I N G, Dake a n d Pearl, M i n e ra l og i st Publishing Compa ny, Portl a n d , Ore., 1 954. A short, a b u n d a ntly i l l u strated guide. T H E LAPI DARY J o u R N AL, Pa l m Desert, C a l . , a bimonthly j o u r n a l of a m a ­ teur collecti n g a n d g e m cuttin g .

RoCKS A N D M I N ERALS, B o x 2 9 , Peekski l l , N . Y., a b i m o n t h l y j o u r n a l d e a l i n g w i t h a m a t e u r activities a n d hobbies. d i a m o n d wheel cuttin g agate

d i a m o nd wheel

91

hamme

r�

interior of boule

SYNTHETIC G EMS-once a d ream-during the past few decades have become a rea lity. Besides the economic problems there were ample scientific ones. Attem pts to make synthetic d iamonds about the turn of the century met with d ubious success. The pro b l e m seems to have been solved by ren ewed efforts i n 1 955. The goa l here was to produce i n d ustria l diamon ds, rather than gems. In this d i rection, a new synthetic, borazon, p roduced i n 1 957 seems to be a s hard as diamond and m u c h bette r a b l e to withsta n d h i g h tem peratures. It is with coru n d u m , how­ ever, that the best synthetic gems have been made. A method of fusing fi n e a l umina (A I 2 0 3 ) in a very hot flame was perfected in 1 902. By a d d i n g the a ppropriate m inera l pigments, synthetic rubies, sapphires, e mera lds, a n d simi­ lar gems of large size a n d fine q u a l ity have been formed. 92

" Emera l d "

" B l u e Zirco n "

"Topaz"

"Spinel"

"To u r m a l i n e "

"Sapp h ire"

SY N T H E T I C D I AMO N D (actual size)

"Aiexa n d rite"

In the apparatus shown on p . 92, the a l u m ina m ixture sifts down through the oxyhyd rog en fl ame and forms a s l ow-growing boule at the e n d of the cera m ic rod. Syn ­ thetic jewe l s a re u n iversa l ly used for watches, a n d it is hard to te l l synthetic corun d u m gems from n atura l ones. Besides the coru n d u m gems, a n u m ber of other syn ­ thetic g e m s have been produced. These a r e chem ica l l y identica l t o the natura l gems. Other m a n - m a d e gems a re without n atura l cou nterpa rts a n d , fi n a l ly, there a re i mita­ tions made of g lass. Gems may a lso be dyed (as ag ates) or have their color changed by heat, chemical action, or radioactivity. A thin layer of precious ston e is some­ times mounted on a larger backi ng of i n expensive ma­ teria l ( p . 1 5) . For these a n d other reasons it i s wise to get expert h e l p when selecti ng va l ua b l e stones. 93

IU>CK.-FOR.M J HG M l WERALS

The m i nerals on this tree are the ones that are of major i m po rta nce i n forming the rocks of the e a rt h 's crust. Some rocks have no defi n ite m inerals-just orga n ic o r g lassy materia l . But most of them do conta in d iscrete m i nerals­ those from the groups pictu red above predom inating. 94

ROC K - FORMING MIN ERA LS ROCK-FO R M I N G M I N ERALS are as m isce l l a neous a

group as the gems. They are im porta nt as the b u i l d i n g b locks of the solid earth, f r o m which mountains a re m a d e a n d va l leys c a rved. T h e y furn ish t h e m inerals of our so i l a n d the s a l t of t h e seas. Most of these m i n er a l s conta i n meta ls, but they are not m eta l l ic ores. S o m e are valued a s gems w h e n , u n d e r r a r e c i rc umsta nces, t h e y atta in gem q ua l ity. A few are of commercial val ue, but it is as basic constituents of rocks (p. 1 09) that the true va l u e of the group is rea lized. Nearly all the rock-forming minerals are s i l i cates, that is, they consist of a meta l comb ined with silicon a n d oxy­ gen. So m e are co m pl ex sil icates, involving severa l meta l s and severa l s i l icate g ro u ps. T h i s com p l exity m a kes chemi­ cal testing of rock-fo r m i n g m i nera l s a difficu l t matter. But the common m inerals of ig neous and meta m o r p h ic rocks can be identified by paying c l ose attention to their physica l properties. I n the rock-fo rming group are some minerals treated elsewhere. Q u a rtz (pp. 76-82 ), especia l ly i n its crysta l l i n e forms, is very common i n rocks. Calcite a n d d o l o m ite ( p p . 63-65) can a lso be ca l le d rock-forming m i nerals; so can h a l ite a n d gyps u m .

a sil icate o f a l u m i­ n u m with boron a n d several other metals, i s occasion a l ly a b u n d a n t with m ica and feldspars i n granitic rocks. It is mostly black-other colors form­ ing gems (p. 8 5 ) . Note the tria n g u la r, striated crystals. H. 7; Sp. Gr. 3 . TOURMAL I N E ,

M I CAS are an u n usua l fa m i ly of m i nera ls, fa m e d beca use

of t h e perfect basa l c l eavage which enables one to cleave off paper-th i n , flexi b l e sheets. Such sheets from large "books" made the "ising lass" heatproof w i n dows of old stoves a n d ranges. Because of their h i g h e l ectriCa l resist­ a n ce, the iron-free m icas are widely used in many kinds of e lectrical a n d e lectron ic equi pment. This i m porta nt use has led to the experimenta l prod uction of a rtifi cia l m icas. Micas a re s i l icate m i n erals. A l l i n c l ud e oxides of a l u­ m i n u m a n d silicon with other meta ls, s i n g l y or in combina­ tio n . They a l so conta in some water i n c o m b i n ation with the oth e r elements. Part of this water (a bout 5 per cent) is l ost when m icas a re heated. Micas a re common i n gran ites a n d s i m i l a r igneous rocks. La rge, six-sided crys­ ta l s-so m e weig h i n g as much as 1 00 l bs.-occu r i n peg ma­ tites. Muscovite, the most common m ica, is mined com­ m ercia l l y i n the Black H i l ls of South Da kota and i n a few other places i n this cou ntry. The best a n d m ost perfect "books" are from large deposits i n I n d i a . M i c a s a lso f o r m i n metamorphic rocks as o t h e r m inerals a re a ltered by heat a n d pressure. The mica i n m ica sc hist a n d in g n e iss is of this orig in , as is the m ica i n some kinds of crysta l l i n e marble.

a re c l a y m i n er­ a l s conta i n i n g water, closely re­ l a ted fa the micas. When they a re heated, stea m farms a n d p ractically exp lodes the fl a ky mineral, expa n d i n g it to many times its ori g i n a l vo l u me. A soft yel low or bronze material, i t is used for i n s u lation a n d for l ight­ weight agg regates. It is excel­ lent for growi n g cuttings a n d seed l i ngs. V ERMICULITES

96

BIOTITE is a d a r k -colored mica, brown o r black, sometimes g reen, conta i n i n g magnesium and iron. I t is a b u nd a n t i n some g r a n ites a n d is a lso common in schists a n d g neiss. Small barrel-sh aped crys­ tals a re sometimes fou n d . Biotite may occur with m u scovite in metamorphic rocks. T h i n cleavage sheets ofte n show light spots, rings, or h a los. H. 2.5-3; Sp. Gr. 2.9.

is a pale, a l most colorless mica - H . 2.2; Sp . Gr. 2.8. It is a potash mica of vari­ able chem ica l composition. Named after M u scovy, where i t was used a s a su bstitute for g l a ss, this com­ mon m ica occurs i n many places. C rysta ls are common and may i nclude fl a ttened g a rnets, q u a rtz, or to u rmaline. A b u n d a n t i n gran­ ites a n d pegmatites. MUSCOV ITE

P HLOGO P I TE, related to biotite a n d fou n d with it, i s a magnesium­ p otassiu m mica often conta i n i n g iron a n d fl uorine. H a rd n ess a n d specific g ravity m u c h l i ke m u sco­ vite. large crystals of p h logop ite are min e d in Ontario and Mada­ gascar. I t is the mica u s u a l ly seen a s b rown flecks i n crysta l l i n e dolo­ m ite and marble.

Bancroft, Onta rio, C a n a d a LE P IDOL I TE is a lith i u m mica with potassium and fluorine, a l so q u ite variable in compositi o n . I t i s a n ore o f t h e l i g h t metal l i t h i u m . S o m e deposits occ u r i n New E n g ­ l a n d ; m o r e near S a n D i e g o , CaL, w h e re o n e fi n d s both a n attrac­ tive lavender a n d a p a l e yellow fa rm. lepidolite gives a crimson flame color.

Keystone, S . D a k .

97

F E L DSPARS f o r m the m ost a b u n ­ dant group of m i n e ra l s. I f t h e group w e r e considered a s i n g l e mineral ( a n d there is g o o d rea ­ son for th is) it wou l d be the m ost common m i n era l by far - five times as common as q u a rtz. Feld­ L A BRADORITE a n i ri­ spars are fou n d i n nearly a l l igne­ descent blue p l a gioclase ous rocks and i n rocks formed feldspar used in ornament a n d decoratio n . from them. A l l a re a l u m i n u m silicates c o m b i n e d w i t h o n e or tw o more m eta ls. Fel dspars have c o m m o n physica l pro perties. Their crysta l forms are very s i m i l a r and the crysta l a n g les are all c l ose to 60 ° and 1 2 0 ° . Feldspa rs show two good c l eavage faces, at right a n g les o r nearly so. Their hardness is 6 o r a bit m o re, and their specific g ravity about 2.6. They usua l ly have a s m ooth , g la ssy, or pearly l uster. Feld spars may be classified by crysta l structure or by chemical com position. Neither is of m u c h h e l p to the a m ate u r. From the chem ica l point of v iew, the potash feldspars (orthoclase and m icroc l ine) a re put in one g roup. T h e other group, conta i n i n g t h e p l a g ioclase feldspa rs, b e g i n s with a l b ite (a sod i u m feldspar) a n d e n d s with a north ite (a calcium feldspar). Between these a re feld ­ spars that a re d ifficult to identify beca use they conta i n varying proportions o f s o d i u m a n d c a l c i u m , as o l igoclase, a n desine, and l a bradorite. Rarer feldspars with barium and other m eta ls a re a lso known to occur. Fel dspars a re widely used i n cera mic i n d ustries i n the m a n ufac­ ture of g lazes, fl ux ena mels, a n d b i nd ers. T h e y ultimately d ecay to form kaolin (p. 49) or other clay m i n era l s (p. 1 50). -

98

a fairly common fel dspar, is usually w h i te, ye l l ow, o r p i n k . I t is a potash feldspar, some varieties conta i n i n g sodi u m ; i n o t h e r s barium may replace t h e potassi u m . A va riety known as a d u l a ria, with a bluish reflected sheen, is sometimes cut a s moo n ­ stone, a semip recious sto ne. An­ other variety, s a n i d i ne, is fo u n d i n volca n i c rock.

ORTHOCLASE,

MICROCLINE is a lso a potash feldspa r-the most common one. Both i t a n d orthoclase lack the fi n e l i nes o r striations seen o n the cleavage faces of p l a g ioclase feldspars. Microc l i n e is a lso fou n d i n a p a l e green color (amazon ite, p. 88), sometimes of gem q u a lity. The best c rysta l s a re from granites near Pikes Peak. A L B I TE is o n e of the p l agioclase feldspars. I t is a sod i u m feldspar with a slightly lower specific g rav­ ity than others, and freq uently contains potassiu m . The basal cleavage s u rface i s ma rked with fi n e lines.. Color wh ite, g ray, o r b l u ish, ofte n w i t h a b l uish sheen. Some are cut a s moon ston es. AI· b ite is common i n g r a n itic rocks and i n acidic lavas.

A lbite tw i n n i n g

is a calcium feldspar which ends the series beg i n n i n g w i t h a l bite. Betwee n t h e m is o l i ­ goclase, w i t h 1 5 to 25 per c e n t calcium. O l igoclase is common i n East Coast g r a n ites. Anorth ite is less com m o n ; it occurs i n seve ral forms, mainly wh ite, g ray, o r glassy. Sma l l a m o u nts of sod i u m a re u s u a l l y p resen t. ANORTH I TE

99

Massac h u setts

ACT I N O L I TE - g reen; fi b rous or radiating, g l a ssy crystals. HORNBLE N D E H . 5 to 6; Sp. Gr. 3 to 3.4. C rystals com mon. Massac h u setts TREMOLITE-white, g ray, o r colorless; usually l o n g , bladed crysta ls.

AMP H I BO L E S are comp lex hydrous s i l icates conta i n i n g

c a l c i u m , mag nesium, a n d i r o n . C rysta l s a re often long o r need l e - l ike; sometimes fibrous (p. 7 5 ) . W h e n s h o rt, they a re six-sided. The c leavage p l a nes a re a t about 55° a n d 1 25 ° , form ing wedge-shaped c leavage frag m ents. These cha racteristics a re i m porta nt i n separati n g a m phiboles from pyroxenes ( p . 1 0 1 ). Horn b l e n de, dark g reen to b lack a n d g la ssy, is fo u n d in basic igneous rocks a n d i n such a l tered rocks as horn blende sch ist. I t conta ins a l u­ m i n u m a n d is most often of secondary orig i n . Act i n o l ite a n d tre m o l ite may be considered o n e m i n ­ era l o r two . The crysta l forms a re the sa m e but i n actino­ l ite some of the m a g n esium is rep l a ced by i ron, giving the m i n e ra l a green color. Both a re secondary m i n e r a l s related to a m p h i b o l e j a d e s a n d asbestos (p. 75). 1 00

ENSTATITE H . 5 . 5 ; Sp. Gr. 3 . 5 . C o l o r va riable.

H . 5 to 6; Sp . Gr. 3 . 5 . G reen to black; g l a ssy.

AUGITE

H. 5 to 6; Sp. Gr. 3.4. C o l o r , white to g reen a n d b r o w n - sometimes tra n s p a r e n t.

DIOPSIDE

PYROXENES a re comp lex s i l icates, c l osely related to the a m phibo les. Pyroxenes a re often fo u n d as primary minerals in i g n eous rocks. Their c leavage a n g les are c l ose to 90 ° , g iving squar.ed c leavage frag ments. They too a re ofte n fi brous o r need l e - l i ke. Most a re gray or green, grading into b l ack. The kinds of pyroxe nes are not d istin ct. They vary chemica l ly as iron replaces ca l c i u m a n d m a g nesiu m . When this occurs, enstatite becomes hypersthene a n d d iopside becomes heden bergite. En­ statite is sometimes f o u nd i n m eteorites from o uter space. Diopside, usua l l y a l ig h t g reen, is m ost common i n m eta­ morp hosed d o l o m itic m a r b l es. Aug ite, the m ost c o m m o n pyroxene, is a c o m p lex of a l u m i n um , m agnesi um, ca l c i u m , a n d iron sil icates f ound i n n e a r l y a l l b a s i c i g n e o u s rocb and dark lavas, d i kes, and s i l ls.

101

Z E O L I T E S a re not major rock formers but they a re wide­

l y distributed. All are chem ica l l y related to the fel dspars -with the a d d ition of water, chemica l ly combined. This water is held l oose l y, so a l l zeo l ites boil and b u b b l e w h e n h eated by a b l ow p i pe. T h e i r n a m e means "boi l i n g sto ne." About 25 m i n e ra l s fit into the zeo l ite g ro u p . I n a d d ition there a re severa l zeol ite associates- m i nera l s c h e m ica l l y s i m i l a r but n o t o f t h e zeo l ite pattern. Zeo l ites a n d their associates are often fou n d i n lavas, fi l li n g cavities a n d veins. A l l a r e pale, fa irly soft m inerals o f l o w density. The a b i l ity of zeo l ites to interc hange i o n s of calcium a n d sodium has prom oted the man ufa cture of a rtifi cia l zeo­ l ites for use a s water softeners. Sti l b ite often occ u rs i n pearly, s h eaflike m a sses of twi n n ed crysta ls. Rad iati n g c rysta ls, often tra n s l u cent, m a y a lso form ro unded knobs. Color: w h ite, yel low, to reddish-brow n . H . 3.5 to 4; Sp. Gr. 2 . 1 . C h a bazite occurs with sti l b ite, usua l l y i n the form of large rhombohedra l -a l m ost cubic-crysta ls. It is w h ite, occasio n a l l y pink, with a g lassy l u ster; tra nsparent or tra n s l ucent. H. 4 to 5; Sp. Gr. 2 . 1 . N atrol i te forms slender, prismatic n eed l e - l ike crysta ls. I t fuses i n the heat of a c a n d l e fl a me-a d istin g u i s h i n g c hara cteristic . C o l o r, w h ite t o yel lowish. H . 5; Sp. Gr. 2 . 2 ; l u ster, g la ssy. Pecto l ite is seen i n ta pering masses of t h i n need l es sometimes severa l inches l o n g . H . 5; Sp. Gr. 2 . 8 . Color usuall y w h ite; l uster silky. It is a l so fi brous o r m a y form radiating masses. Pecto l ite needles a re d a n g erously sharp a n d s h o u l d be h a n d led with ca re. Prehn ite and pecto l ite a re zeo l ite associates w h i c h may occ u r together. Prehn ite is usua l l y i n compact m a sses of flat l i g ht-green c rysta ls. luster, g l a ssy; b rittle and trans­ l ucent. H . 6 to 6.5; Sp. Gr. 2 .9. 1 02

Pen nsylva n i a ST I LB I T E New J e rsey

NATRO L I T E- Oregon

PECTOLITE P R E H N ITE-New J e rsey

1 03

GARN ETS are better known as gems tha n as rock-fo rm­

i n g m i n erals, but they a re common a n d form a sma l l but conspicuous i n g redient of igneous and meta m o r p h i c rocks. Ga rnets are a c l ose -knit fa m i ly of s i l icate m i nerals with many common cha racteristics. They a l l form crysta ls i n the isometric syste m , usu a l ly w i t h 1 2 or 2 4 sides, t h o u g h sometimes com b i ned forms w i t h 36 o r 4 8 faces are fou n d . Chem ica l ly, garnets conta i n the elem ents calcium, magnesium , iron, a n d a l u m i n u m , combined with silicon a n d oxygen. Other, less common meta ls may a l so occur.

i n p hy l l ite- Pen nsylva n ia

GROSSULARITE i s a calcium­ a l u m i n u m garn et, normally c6lor­ less to w h ite, but colored w h e n i t conta i n s i ron a s a n i m p u r ity. It is fo u n d m a i n ly i n m a r b l e . A warm-brown va r iety from Ceylon i s cut as a g e m . The name refers to a Siberian "goosebe rry g reen" va r iety .

is sometimes ca l led precious g a r net, t h o u g h it is mined i n l a rg e q ua ntities for g a r n et paper. C l ear, perfect specimens are found in South African " b l u e earth" with dia­ monds; they make fine gems. Pyrope is a magnesium-alu­ minum garnet.

PYROPE

cut g e m

c rysta l

i s the "common garnet" fo u n d i n many metamor­ p h i c rocks. I t i s a n i r on -a l u m i n u m g a rnet, t h o u g h part of the i ron may be replaced by mag nesium­ making such forms similar to pyrope. When i t has a c l e a r red color it is sometimes-like pyrope -ca l led p recious g a r n e t a n d is cut as a gem.

ALMANDITE

crysta l s in m ica sch i st, N e w Yo rk

Crystals are abundant-from pinhead size up to 4 in. in diameter. Fresh crystals have a glassy luster. There is no distinct cleavage. All garnets have a hardness of about 7. Their density is more va riable, between 3 . 4 and 4.3depending o n the metals i n them. Most garnets are found in schists, gneiss, and marbles. Some occur in lavas and in granites. Only a small percentage of garnets are of gem qual­ ity. In a few large deposits, garnets are mined and crushed for garnet paper and other abrasives.

is q u ite a rare member of the group of a l u m i n u m garnets. I t co ntains manga nese and a l u m i n u m . The m a n g a nese ofte n g ives t h e g a r net a violet t i n t which ma kes g e m - q u a l ity speci­ mens pa rti c u l a r l y v a l u a b l e . Such gem·q u a l ity stones have come from V i r g i n i a g r a n ites. SPESSARTITE

c rysta l i n s c h i st

is a g a rnet conta i n ­ i n g ca l c i u m a n d i r o n . It, t o o , i s ve ry co m m o n a n d l i ke a l m a n d ite is called common g a r n et. C o l o r v a r i e s f r o m y e l l o w to g reen, red, and b l o c k, depen d i n g o n i m p u ri­ ties. It occurs i n igneous rocks and i n some meta m o r p h osed l i mestones. The g reen form, de­ m o n toid, i s a gem (p. 8 5 ) .

ANDRADITE

is a l e s s common ga rnet fo u n d i n serpentine rock and i n l i mesto nes a ssociated with chro m i u m ores. I t is a c a l c i u m · c h romi u m g a r net. T h e ch romi u m g i v e s i t i t s rich g reen color. I t i s u n l i ke m o s t g a r n ets i n that a s p l i nter of it w i l l n o t fuse when h eated with a blowpipe.

UVAROVITE

1 05

crysta l

0. 1 i n .

O L I V I N E, a lso ca l le d

c h rysol ite or peridot, is the most common member of a g ro u p of s i l icates. O l ivine is a m a g n es i u m-iron s i l i­ cate, colored various sha des of g reen (ra rely, brow n ) ; H. 6.5 to 7; Sp. Gr. 3.3. L uste r, g lassy; trans ­ parent to tra n s l ucent. C le a r vari­ eties a re cut as the g e m peridot. O l ivine is fo u n d i n igneous rocks J ackson Cou nty, N .C . that are rich i n m a g nesium a n d low in q u a rtz, as basa lt a n d g a bbro; a lso i n m eta mor­ phosed d o l o m ites. It is often found i n the form of sma l l g r a i n s o r i n l a rge, g ra n u l a r masses. The c rysta ls are relative l y ra re, though occasio n a l l y some have been found u p to severa l inc hes long . C H LO R I T E is o n e, two, th ree, or more m i n e r a l s depe n d­

i n g on how ca refu l l y th e constituents a re separated. If considered a s i n g l e m i n e r a l , c h l orite is a m ixture of mag­ nesium a n d iron-a l u m i n u m s i l i cates, with water. It often forms as an a l teration of rocks rich i n pyroxen es, a m ­ p h i b o l es, a n d b iotite. It may a lso f o r m i n cavities of basic igneous rocks. C h l orite is usua l l y g reen but may vary from w h ite to b rown and b l ack. H. 2 to 2 .5; Sp. Gr. 2 . 8 ; pea r l y l u ster; streak, g reenish or w h ite. It forms in masses, crusts, fi bers, o r b l a ded crysta l s . The crysta l s have a per­ fect basa l c l eavage a n d, l i ke m ica, s p l it i nto t h i n s heets. These may bend s l i g ht l y, l ike se len ite, but a re not e l astic l i ke mica. 1 06

FOLIATED SERPENT I N E Pennsylva n i a

VERD ANTIQUE

carved serpe ntine baok end

C OMMO N S E R P E NT I N E - N o rway

S E R P E NT I N E (chem ica l l y s i m i l a r to c h lo rite) is a mag­

nesium s i l icate with water, but may i n c l ude sma l l a m o u n ts of iron or n ic k e l . The fi b rous form of serpentine, c h ryso­ tile asbestos, is described o n p. 7 5. A n u m be r of other varieties depend o n physica l cha racteristics, especia l ly color a n d l u ster. C o m m o n or massive serpentine (H4Mg 3 S i 2 0 9 ) va ries from cream wh ite throug h a l l shades of green to b lack. Strea k is wh ite. H . 2 .5 to 4; Sp. Gr. 2 .6; tra n s l ucent to opaque. Note the g reasy o r waxy l u ste r a n d fee l of serpentine. Some weath � red spec i m e n s a re earthy. There a re m icaceous, fi b rous, a n d mottled va rieties, some of them fl uo rescent. The m i nera l serpentine is a seco n d a ry m i nera l w h i c h a l so occurs as m eta morphosed serpentine r o c k . De posits are l a rge but a t present have only m i n o r use in fi rebricks. Serpe ntine m a r b l e (verd a n tiq ue) a n d deeply colored com­ mon serpe n t i n e a re used for carvi ngs. 1 07

STA U R O L I T E is an iron-a l u m i n u m s i l icate often fo u n d with g a r n ets i n such m etamorphic rocks as sch ists, phy l l ites, a n d g n e isses. Brown to twinned crysta ls b lack in color; strea k, g ray; H. 7 to 7.5; Sp. Gr. 3.7. Sta u ro l ite a l m ost a l ways occ u rs in c rysta ls-as ortho­ rhombic prisms and c o m m o n l y as twi n n e d crysta ls. Tw i n n i n g may be at 60 ° or 90 ° . When at 90 ° , the twi n crysta l s form a perfect cross. New Mexico Such crysta l s (fa iry crosses), broken o r weathered from the bedrock, a re so l d as charms or souve n i rs. T h ese may be u p to 2 i n . l o n g , but a re usua l ly an i n c h or l ess. Exce l lent specimens occur in schi sts near Minera l Bluff, Georg i a . Tra nsparent crysta ls occur rare l y, a n d may be cut as gems. E P I DO T E is o n e of a g ro u p of c o m p l e x s i l icates of c a l ­ c i u m a n d a l um i n u m w i t h water. It f o r m s i n n e a r l y every type of m eta morphic rock, in cracks a n d seams, as crys­ tals or a s t h i n g reen crusts. It is a ty pica l m i n e ra l where igneous rocks have come in contact with l i m esto nes. Crys­ ta l s a re usu a l l y s l e n d e r prisms, g ra d i n g i nto need le-like forms. C o l o r, g reen to b rown a n d b l ack; H. 6 to 7; Sp. Gr. 3.3. Easi ly identified by hard n ess a n d color. /•

•.

cryst a l Alaska

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at h i g h temperatu res or from molten materials. Pp . 1 1 0- 1 20. 2 SEDIMENTARY ROCKS o re formed by action of w o.t e r, w i n d , o r o r g a n i c a g e n t s . Pp. 1 2 1 - 1 3 2 . 3

METAMORPH I C ROCK S

hove

ROCKS Rocks are l a rg e masses of material that make u p the earth's crust. Some d o n ot have discrete m in e ra ls but are com posed of g lasses or of organic m ateria ls l ike coa l . Many rocks are not s o l id-as so i l , g rave l , sand , and c lay. A rock may consist of a s i n g l e m ineral, a s q ua rtz, gypsum, or d o l o m ite. Most rocks conta i n several m i n erals, o r were formed from o lder rocks i n w h ic h these m i nerals were present. 1 09

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pota s h

pota s h

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m i ca s pyroxene amphibole

micas pyroxene amphibole

biotite m i c a pyroxene a m p h i bo l e

biotite mica py roxene a m p h i bo l e

GRAN ITE

SYEN ITE

DIORITE

GABBRO

FELSITE PUMICE

/

BASALT

OBS I D I AN

/

olivine pyroxene amphibole P E R I DO T I T E

SCOR I A

I G N E O U S RO C K S Igneous rocks are classified by their texture, mineral content, and origin. They all come from magmas-molten mixtures of minerals, often rich in gases, found deep below the surface. If magmas cool beneath the surface they form intrusive rocks and develop typical structures that may later be exposed by erosion. Magmas reaching the surface form extrusive rocks, such as the spectacular volcanic rocks. Igneous rocks usually contain ferro-mag nesian minerals (amphiboles, pyroxenes, micas, or olivine) and feldspar or feldspar-like minerals. Many contain quartz. Those rich in light minerals (quartz and potash feldspar ) are called acidic. These are light not only in color but in weight (average Sp. Gr. 2 . 6 to 2.7). Those richer in ferro-mag­ nesian minerals are called basic. They ore darker and heavier (Sp. Gr. 3 . 0 and more) . In texture, igneous rocks range from those with large crystals to glassy rocks with no crystals at all.

1 10

I NT R U S I V E ROCKS form as magmas cool. This is a gradual process in which the more volatile chemicals re­ main as · liquids and gases lo nger. Some intrusive rocks, very near the surface, grade into extrusive types. Those that cool deeper are more coarsely crystalline. G r a n i te is the best known of the deeper igneous (plutonic ) rocks. It is usually light-colored, formed mainly of potash feldspar (about 60 per cent) and quartz (about 30 per cent}, usually with mica or hornblende. The inter­ grown mineral crystals are all about the same size-a characteristic of slow cooling . Fine granite has a salt-and­ pepper pattern. Feldspar may redden it. Granite is hard and tough, widely used in con struction and monumen ts. Some granites may be metamorphic rocks (p. 1 40 ) .

M E D I UM-G R A I N E D GRAN ITE

F I N E- G RA I N E D GRAN ITE

R E D G RA N I T E M i n n e sota

111

O T H E R I NT R U S IVE ROCKS include some w h ic h have

cooled near the surface. These may conta in a g roundmass of crysta l l i n e grains surrou ndi ng l a rger crysta ls. Such igneous rocks made of crysta ls (phen ocrysts) i n a fi ner groundmass a re known as porphyries. Porphyries a re PEGMATITE i s a coa rse-g rained v e i n o r d i k e rock w i t h crysta ls that range f r o m a n i nch o r so t o many feet i n l e n gth. Pegma­ tites are mined for the i r mica a n d feldspar, o r fo r gems a n d other accessory m i nerals. They often co nta i n cavities or vugs lined with crysta ls. In o n e fo rm, graphic gran ite, the q u a rtz fa rms a n g u l a r fi g u res which look l i ke writi n g . Some aece ssory pegmatite minerals:

Shel by, N . C .

garnet

arsen o p y r i te

a patite

tourma l i ne

emerald

to paz

l e p i d o l ite

c r y o l ite sapphire

spodumene

bery l

ch rysobery l

ruby

mo l y b d e n i t e

r u be l l ite

p y r i te

aquamarine

w o l f ra m i te

fl u o r i te

ca ssiterite

u ra n i n i te

is less common t h a n g ra n ite. I t lacks q u a rtz entirely or m a y have a sma ll amou nt, i n w hic h c as e it i s k n own as q u a rtz-syen ite. Syenite is mainly potash feldspars with some mica or hornblende. The crystals are usually s m a l l a n d the rock is even-textured. Syenite a lso forms por­ phyries with phenocrysts of feldspar.

SYENITE

Wa u s a u, Wis.

St. Cloud, M i n n .

1 12

GRANITE PORPHYRY, which fo rms u n d e r somewhat different conditions f r o m gran ite, has a granite g r o u n dmass i n which phe no­ crysts of feldspar, q u a rtz, o r biotite mica a re embed d e d . A porphyry i s named after the matrix o r groundmass-such a s syen ite porphyry, basalt porphyry . They a lso occur i n extrusive rocks (p. 1 1 6) .

fo u n d in intrusive rocks formed near the surface, a n d in ex­ . trusive rocks, b ut do not occur in dee p-seated i n trus ives. Peg matite, g ra n ite, and syen ite a re l i g ht-colored intru­ sives. Diorite, g a b b ro, a n d peridotite a re d a rk, with more ferro- magnesian m i nerals. is a basic rock rich in m i nerals such as a m p h i boles, biotite, o r pyroxenes. II> texture is like that of g r a n ite, b u t it is composed m a i n ly of plagioclase fel d spa r a n d ferro-magnesian m i nerals. Oth e r fe ld­ spars may b e p resent, a n d sometimes a bit of q u a rtz. I ts color is usually g ray or d u l l green. Granites grade i nto dio rites through intermediate fo rms-the g rano­ d i o rites. DIOR I T E

like d i o ri te, has a g r a n itic tex­ tu re. Since texture depends upon rate of cooling, rocks of gabbro com position vary from fi ne-grained (diabase) on the out­ side of a dike o r sill (p. 1 1 4 ) to o typica l g a bbro with i n . Gabbro is mode mai n ly of plagioclase feldspa r a n d pyroxene, with some olivine, traces of i l m e n ite, but no q u a rtz. A dark rock, its m i n e r a l crysta ls o r e d e e p l y i n termeshed, m a k i n g it o very t o u g h r o c k . Porphyritic g a b b ros a re rare. Dolerite (or d ia b a se) is the fi n e-g rained g a bbro w h ich often occurs i n s i l l s o r d i kes. I t grades i n to basa l t at the edges, where it has coo led more raoidly .

S o l e m , Moss.

GABBRO,

is a dark, heavy intru sive rock composed m a i n l y of olivine with pyroxene and tiny flecks of p h logopite m ica or horn­ blende. Little o r n o fe ldspar is p resent. F resh rock i s n e a r l y black, b u t the more common weathered speci mens a re g reen ish and softer. Peridotite a l te rs i n to serpentine. The South African diamond deposits occur i n perid otite, which, i n other places, con­ tains im porta nt de posits of nickel, chromi­ um, and plati n u m .

Salem, Mass.

P ERIDOTITE

Baste, Harz Mts., Germany

113

I NT R U S I V E RO CK ST R U C T U R ES are the natura l forms taken by intrusive rocks. Sometimes these structures form deep beneath the surface. With the passing of time, they may later be exposed as covering rocks a re rem oved by water, ice, o r wind. When i ntrusive structures a ppea r at the s u rface t h ey may beco m e specta c u l a r features of the l a n d scape. As they weather they produce typica l kinds of soil. Rich ore deposits formed with their i ntrusion may then becom e available.

Palisades o f t h e H udson (sca l e distorted)

D I KES a re sheetlike intrusions rising from a batholith (p. 1 1 5 ) o r from some other source of m a g m a . These sheets may va ry in thickness from a few i nches to h u n d reds of feet, and may extend from a few feet to many m i l es. The magma formi n g the d i k e fol l ows cracks a n d joints below the s u rface, hence d i kes cha racteristica l l y cut a cross the rock structu res. Magma cools rapidly i n contact with the s u r rou n d i n g rock. Hence the dike may d iffer i n texture a n d composition i n t hese contact zones. T h e heat of the i n jected materia l may meta morphose the a d j o i n i n g rock (p. 1 39 ) . Miles of well­ developed d i kes a re exposed near Spanish Peaks, Colorado. ·

are s i m i l a r in origin to d i kes. W h i l e d ikes cut across the existing rocks, s i l l s f o r m para l lel to them, frequently s h o u l ­ dering their way i n between layers of sed i ­ mentary rocks. I f t h e s e layers a re tilted, the s i l l w i l l be tilted also. The P a lisades along the H udson River near N ew York is a tilted sill of d i a base and gabbro. Sills a n d d i kes may occur near volca noes when lava fills u p cracks i n p revious lava flows. Joints fo r m i n g reg u l a r 5- or 6-sided col­ umns mark some fi ne-g rained intrusive rocks, as i n the Giant's C a u seway i n I re­ land and Devi l's Tower in Wyoming.

S I LLS

I n trusive structu res originate from deep reservoirs of m a gm a whose o r i g i n s are sti l l not clear. Mag m a s a re capa b l e of producing both acidic a n d basic rocks. Acidic rocks tend to form m a jor structures-batho l iths, the cores of m o u n tain ra n ges, and the g reat contine nta l s h i e lds. Basic rocks o c c u r m o re freq uently i n d i kes and s i l ls, often g rad ing into extrusive rocks. A l l extrusive rocks, at o n e p l a c e or a n other, g ra d e or j o i n into i n trusives. Recog n i z i n g such structures e n a b les one to interpret the l a n d scape. m i g h t be l i kened t o b l isters with i n the e a r t h ' s thin skin of sed i m entary rocks. M a g m a spreads o utward between rock layers and ra ises those a bove it into a dome that may be a thousa n d feet o r more h i g h a n d f r o m one to te n m i les across. Sedi mentary layers lifted by the m a g m a may crack, s u bjecti n g them to a more r a p i d erosion w h ich may eventually expose the igneous core. The edges of resista n t u p t u r n e d sed i menta ry layers a r o u n d t h e laccolith may form c i rcu l a r ridges c a l l e d h og backs. lacco liths a r e common i n the West, p a rticula rly i n Uta h . LACCO L I T H S

BAT HOLIT HS, the l a rgest i ntrusio n s, may cover 1 00,000 sq u a re m i les. O u r l a rg est, i n central I d a ho, spreads over 1 6,000 square m i les. I n the Rockies a n d S ierra Nevada batholiths a r e exposed i n the m o u ntain cores. T h o u g h some are ancient, some are new, i n d icati n g t h a t they a re part of the conti n u a l b u i l d i n g u p of the earth ' s crust. As magma wells u p it may d issolve some of the s u r ro u n d i n g rock. I t may spread u neven ly, tra p p i n g islands of o l d e r rock. Batho liths g e n e r a l l y conta i n coa rse-g rained rocks. T h ey are deeply b u ried a n d may not be u n covered fo r m i l l i o n s of yea rs. Sm al l batholiths a r e c a l l e d stocks.

EXT R U S I V E ROCKS em brace a large g roup, the m ost common member of which is l ava . T h is m o lten materia l pours o u t through fi ssures a n d volca n oes. It s p reads i n g reat lava fl ows o r b u i l d s u p cones. Volca n ic explosions th row fra g m e nts i nto the air as volca n i c ash o r volca n ic bombs. The forms a n d structu res of these rocks are shown is a l i g h t-co lored acidic rock which has very much the same c hemical composition a s g r a n ite. Its texture i s very fi n e . When m i n e ra l s can be seen in it­ p h enocrysts of q u a rtz a n d a g l a ssy fe ld­ s p a r (sa n i d i n e)-the rock i s a rhyol ite par· phyry. Color wh ite to p i n k to g ray, though often reddish from i ron sta i n s .

RHYOLITE

RHYOLITE-Colorado

a re chemically the same as rhyol ite. Obsi d i a n o r natu ral glass is formed w h e n rhyolitic lava is q u ickly chilled. Though it i s da rk-co lored, t h i n fragme nts a re light and transparent. I n d ians made k n ives, a rrowheads, a n d or­ n a ments from this unusual rock . Pitch sto ne is a d u l l e r, ro u g h e r form of obsi d i a n . Rhyo­ l ite lava blown to a spongelike consiste ncy by the release of gases fo r m s p u mice-a volcanic frot h . Pumice i s so light it floats o n water, a n d frag ments may be washed ashore far from the volcano.

OBSIDIAN a n d PUMICE

O BS I D I A N -Wyo m i n g

is n a med for the A n d es Moun· tains, where it i s ubundant. I t contai n s l ittle or no q u a rtz, a n d has a greater p ro­ portion of ferro-magnesian m i n e r a l s, w h ich give the rock a d a r k e r color than rhyolite. Porphyries a re common, with phenocrysts of feldspar or dark minerals. Andesite is i n ter· mediate i n compositi o n between rhyolite a n d basalt. Si nce rhyolite a n d a n d esite are d ifficult to d i sti n g uish i n the fi el d, the term felsite i s used for both w h e n more accurate i d entification is imposs i b l e .

ANDESITE

P U M I C E-M i l l a rd Co., Utah

ANDESITE

1 16

on pp. 1 1 8- 1 1 9. I n color the rocks themse lves may be l i g h t (acid ic) o r dark (basic). Like intrusive rocks, the extrusives g ra d e from those rich in q u a rtz to those with no q ua rtz at a l l . Most of the rocks are fi n e-grained beca use of rapid coo l i n g , and a re difficult for the amateur to ide ntify and c l a ss ify. BASA LT i s the co m m o n dark, h eavy lava that i s widespread the world over. I t is m a i n l y pyroxene and a p l a g ioclase feld­ spar, b u t the texture is so fi n e that these i n d ivid u a l minerals eire ra rely see n . Olivine may also be present. In tota l, the rock is a bout half fel d spar, half ferro·.magnesian m i nerals. Basalt varies from a d a r k g ray with a greenish tinge to a l most black. I n a r i d regions exposed basalt su rfaces fre­ q uently d evel o p a w h ite, l i my encrusta­ tion. In h u m i d a reas the iron i n basalt oxidizes, coloring t h e su rface a ru sty brown. I n a d d ition to t h e d ense r o c k fou n d i n l ava flows, d i kes, a n d s i l l s, b a s a l t has sev­ e r a l other forms. U p pe r su rfaces of basaltic fl ows may co ntain gas b u bbles w h ich form a porous and c i n d e ry rock called scoria. later the holes o r vesicles may become fo i led with m i n e r a l s such as calcite, agate, a n d a m ethyst, a s well a s zeol ites. When t h e o p e n i n g s are a l m ond-shaped the n a m e amygdaloidal b a s a l t is u s e d . large d eposits of native copper h a ve been fo u n d i n such basalts, especially in Mich i g a n .

Somerset C o u n ty, N . J .

a ri d weath ering

AMYGDALO I DA L BASALT

1 17

VOLCANOES A N D LAVA F LOWS are the str.uctures

most typic a l of extrusive rocks. The Col um bia lava p latea u, consisting of a large n u m ber of lava fl ats, covers over 200,000 square m i l es; in places it is up to a m i le thick. Volca n i c cones vary from steep cinder cones ( 1 ) rare l y 1 000 f t . high t o sma l ler spatter c o n e s (2) a n d l ow, broad shield lava cones (3) with s lopes of o n l y a few deg rees. Most volca n oes a re compou n d (4), with cind ers, ash, a n d broken fragments ( b reccias) interbedded with lava (see below). Some have radiating dikes of basalt (5); others a re associated with extensive lava flows (6).

Pahoehoe is the Hawaiian n a m e for a fl u id lava which flows freely and coo l s with a smooth, ropy surfa ce. Such lava flows look l i ke frozen rivers of b lack, tinted with iridescen t purple. Viscous Lavas form crusts which break a n d rol l over. This j u m b le, m ixed with scoria, forms sha rp, jagged fl ows. Such l ava is ca l led aa, a nother Hawa iian name. Volca n ic lavas have been studied i ntensively at Mauna Loa and K i l ­ auea, b o t h s h i e l d cones. V o l c a n i c Bombs a re ma sses of l i q u i d lava thrown into the a ir. Their motion g ives them the el on­ ga te shape a n d s mooth s u rfa ce. Active volcan oes th row vast q uan­ tities of gases a n d steam into the a i r as we l l as d ust, ashes, and frag­ ments ra n g i n g fro m la p i l l i ( less than 1 i n . ) to- b l ocks weig h i n g tons. L a v a Caves and T u n n e l s form when a stro n g crust ha rdens under w h ic h the l iq u id lava keeps flow­ ing, leaving a h o l low. Crude caves form i n ove rturned m asses of aa lava. I n some, dripping lava forms sta lactites. Ice a n d snow which fi l l some l ava caves i n w inter a re so protected that they do not melt by summer - m a k i n g "ice caves," a tourist attracti o n .

C raters o f t h e Moo n , I d a h o

· New Mexico

I G N EO U S ROCKS have long been known to be associ­ ated with m eta l ores. Hot l i q u ids and gases from magmas coo l to prod uce o res d irectly, or form ores as they react with the loca l rocks they penetrate. Co ntact d e posits a re formed aro u n d the edges of batho l iths or other l a rge in­ trusions, especia l ly when these have penetrated i nto l i m e­ sto nes. Ve ins may extend from ig neous masses i n to the loca l rock, ca rrying m i nera l izing l iqui ds a n d g a ses. A sys­ tem of veins w h i c h can be m i ned as a unit forms a lode, like the fa mous Mot her Lode of C a l ifo rnia g o l d days. Other veins form as m i n era l i z i n g so l utions penetrate cracks a n d deposit ores in natura l openings o r zones of crushed rock. Most primary ores are sulfi des. These a n d other o res ofte n occur i n specific m i n e ra l associations. One exa m p l e i s t h e lead-zinc deposits of Ka nsas a n d O k l a homa (sp h a l ­ erite, g a l e n a , a n d many accessory m i n e ra ls), a n other i s t h e z i n c , iron , a n d manga nese deposits at Fra n k l i n , N . J . ; a t h i rd is the iron-tita n i u m ores of the Adirondack s.

1 20

SE D IMENTARY ROCKS S E D I M E NTARY ROCKS are extremely varied, d iffering

widely i n textu re, col or, and com positio n . Nearly a l l a re m a de of materia l s that have been m oved fro m a p lace of orig i n to a new place of de positio n . The d ista n ce m oved may be a few feet or thousands of m i les. R u n n i n g water, w i n d , waves, currents, ice, and gravity m ove m ater i a l s on the s u rface of the earth by action that takes place o n l y o n o r very near the surface. I n tota l these r o c k s cover a bout t h ree- q u a rters of the earth's s u rface. U n consol idated mud or sa n d is usua l l y referred to as a sediment, w h i l e consolidated materia l s are ca l le d sed­ i m e nta ry rocks. Rocks m a d e u p of g ra i n s or pa rticles a re cal led c l astic; they may range from less than a tho usa n dth of a n inch to huge b o u l ders. Other sed i m e ntary rocks a re of c h e m ica l or o rg a n ic orig i n . Most sed i m e ntary rocks form i n layers o r strata ; m a n y conta i n fossi l s. Major sedi· menta ry strata form slowly over m i l l ions of years. 121

Great Wh ite Throne (sa n dsto ne) at Zlan National Park, Utah.

SAN DSTO N E is formed by the action of wind, water,

and ice o n o l d e r rock. It is m a i n ly grains of q ua rtz cement­ ed by s i l ica, l i me, or iron oxide. S i l ica cement m ay produce h a rd, durable sa ndstones; the other ceme nts a re n ot as resista nt. Sa n d stones g rade off on the coa rse side into c o n g l omerates (p. 1 28) and on the fi ner side i nto sandy s h a l es (pp. 1 24- 1 25). Most sa ndsto nes formed in sha l low seas a n d show sig ns of near-shore orig i n -they often in­ clude foss i l ripplemarks a n d she l l s of sha l l ow-water a n i­ mals. I n some san dsto nes, nod u l es of soft l imonite o r hemat ite f o r m "paintpots" once u s e d by I n d ia ns. 1 22

M E D I UM-GRA I N E D SANDST O N E N e w Yor k

SAN DSTO N E cemented b y iron oxide- U tah

A R KOSE-showi n g fe ldspor g r a i n s M t . Tom, Mass.

" I nd i a n paint pot" Glen C ove, N.Y. C ross-bedded sand ston e fo rmed from a ncient d u nes-Kanab, U ta h .

Livingston County, N.Y.

Kent. N . Y.

SHALES or m udstones a re m a i n l y c l ays w h ich have hard­

ened i n to rock. Sha les may grade into fine sa n dstones o r, when m uc h lime is prese n t, into s h a l y l i m esto nes. Since c l a y particles a re exceedi n g l y fi n e, they tend to be ca r­ ried into deep or q u iet water. S h a les are often t h i n-bed­ ded o r l a m i nated, with fairly u n iform texture. Their color is usua l ly gray, but varies from b l ack to d u l l red. C lays a n d sha les are freq uently so fi ne-g ra ined that they serve a s a barrier to movem ents of water. C lays a n d si lts t h a t f o r m i n lakes may s h o w d a r k a n d l ight a lternating layers c a l l e d va rves, each pair of layers representing a year's de posit. By counting the va rves t h e age of g lacial l a kes and other depos its can be esti mated. For i n stance, va rve cou nts i n d icate that the sha les of the Green River formation in Wyo m i n g took over 5 m i l l ion yea rs to form. Other structures fo u n d i n sha les a re shown o n the next page. S h a les are used in the m a n ufacture of cement. U n ­ consol id ated clays (p. 1 5 1 ) a re of tremendous va l ue for cera m i c a n d other uses. Since c l ays a n d sha les a re com ­ m o n l y f
I RO N C O N C R E T I O N

S E PTA R I A N C O N C R E T I O N (cross section) Texas C O N C R ET I O N - S a n d usky, O h i o are ofte n fo u n d i n sha les, s a ndstones, a n d l i me­ stones. They may b e spherical or flattened m a sses fo rmed a r o u n d a fossi l or some other n ucleus. They CO N CRET IONS

may be ve ry sma l l or u p t o sev­ eral feet i n d i a m ete r. C oncretions are often h a r d e r than t h e e n ­ closing r o c k a n d h e n c e a r e fo u n d as they w e a t h e r out of it. form as d eposits of m u d a n d clay in shal low l a kes o r o n m u d fl a ts d ry i n the s u n . The shrin kage forms rou g h six-sided blocks. later fresh mud may be washed into the s h r i n kage cracks. M u d cracks i n d icate the sha llow­ water origin of the rock.

MUD CRACKS

raind rop i m p r i n ts i n ,sh a l e I llinois

fa l l i n g on m u d or clay of j ust the right consistency w i l l leave s ma l l pits. C o n ti n ued rain w o u l d wash th ese away, but a brief shower fol l owed by a period of d ry n ess may p reserve rai n d rop i m pressions. These are rarer and h a rd e r to find than mud cracks.

RAINDROPS

1 25

LIM ESTO NES a re exceedingly va riable in color, texture,

and origin. They consist m a i n l y of the m inera l ca l c ite (p. 63) and react l ike calc ite chemical ly. Most of them are of marine origin-some for mi ng at great d epths . Both p l a n t a n d a n i m a l l ife, d i rectly a n d i n d i rectly, contribute t o t h e i r formatio n . Ma ny kinds of a n ima ls contribute the m i nerals that form l imestone-cora ls, worms, crinoids, m o l l u sks, a n d certa i n protozoa. A l g a e a re a l so i m portant l i me-precip­ itating p l a n ts. Some limestones a re chem ica l preci pitates, w h i l e others a re cemented fragments of l i m e . A u n iq u e a n d complex natura l balance is k n o w n to i n ­ v o l v e the carbon-d ioxide content of t h e a i r, the carbon­ d ioxide a n d l ime d issolved in the sea, l im esto n e formation, and c l im atic change. Limestone rocks a re a keyston e in this structure because they a re g reat reservoirs of carbon d ioxide as wel l as of l i me. Since lime i s so l u b l e in acid water, l im estones d issolve and recrysta l l ize easily. They S HE L L LIME STONES include coq uina, formed recently of shells a n d fragments loosely cemented. Chalk is a limesto ne made of tiny p rotozo o n shells. Older shell l i mestones may contain fossil brachiopods, bryozoans, corals, a n d crinoids. Some of the o ldest known sedimentary rocks a re l ime­ stones formed from a l g ae.

L IME STONES usually consist of a mass af s m a l l concre­ tions, each b u i l t up layer upon l ayer around some small n ucleus. The res u l t i n g rock is composed of spherical grains. Ool itic lime­ stones may be formed i n sha llow water. Each g ra i n g raws a s it is railed by waves o r c u r rents. OOLI T I C

lodlatlo

} 26

weather ra p i d ly in h u m i d c l i mates; very s l ow l y in arid o nes, where they a re good c l iff formers-as at G ra n d Canyo n . limesto nes v a r y f r o m a l most u nconso l i d a ted masses o f s h e l l s ( s u c h as the kind shown on p. 1 26) t o com pact, crys­ ta l l ine rocks. I ntimately conn ected with p l a n t a n d a n i m a l l ife, they are a rich sou rce of fossils ( p p . 1 30- 1 32). l i m e ­ sto nes rich i n clay a re k n o w n as mar ls . They a lso g ra de into sha les a n d i nto san dstones. Some conta i n s i l ica con­ cretions in t h e form of chert, fl i nt, or c h a l ce d o n y ( p p . 8081 ) . A carbonate rock w h ich conta ins c a l c i u m and mag­ nesium carbonate is a d o l omitic l i m eston e o r a true dolo­ m ite ( p . 65) . The econo m ic i m p o rtance of l i m estones is a l m ost be­ yond estimation . Lim esto nes a re widely used for road meta l, i n conc rete, and for l i me. Shaly- l i m esto nes a re a source of cement. Lead, zinc, fl uorite, su l f u r, a n d o i l de­ posits a re often associated with l i m esto nes. i s a l i g h t, p a ro u s l i mestone often colored with i ro n . I t fo rms i r s p r i n gs, where calcite may be d e posited on water p l a n ts, twigs, o r debris. In caves, the seco n d a ry deposit of calci u m carbonate (trav­ ertine) forms flowstone, cove ring w a l l s a n d floor a n d sometimes form ing sta l actites and sta lag­ mites (pp. 63-64) . TUFA

CRYSTA L L I N E

Massa c h u setts

L I MESTONES

form a s l i m e ecrysto l l i zes to o greater or lesser extent. These l imestones ore closely a k i n to marbles {p. 1 34) but o re consid­ ered sed i m e n ta ry rocks when there is no indication that they hove been deformed by p ress u re . C rysta l l i n e l imestones used for decoration and orna mentation o re sometimes sold a s marble. Ohio

1 27

C O N GLOME RATE

C O N G LOMERATES are sed ime ntary rocks com posed of

rounded pebbles on e-fourth of an i n c h in d i a m eter or l a rg e r, cemented in a matrix of fi ne r materi a l . In ti l l ite, a c o n g l o m e rate of consol idated g lacial t i l l , the u n a ssorted fra g m e nts may ra nge from g rave l size to great bould ers. The larger ones may show typica l g lacia l scratches. The coarse materia l s which form c o n g l o m erates a re de posited close to shore at the mouths of swift rivers or canyons, in a l l uvia l fans, or in d e ltas. The pebbles in co n g l omerates a re frequently q uartz o r q u a rtzite. The cement may be iron oxide, s i l ica, calcium carbonate o r, occasiona l ly, clay. C o n g l o m e rates g rade off i n to san dstones. C o n g l o m erates i n which the fra g m e nts are sharp and a n g u l a r because they a re fresh l y b roken and not worn i n tra n s port are ca l led breccias. The various kinds of breccias have l ittle i n common oth e r than the a n g u l a r sha pe of t h e i r components. S o m e a re o f v o l c a n i c origin, some represent cemented materia l s i n ta l u s s l o pes or a l­ l uvia l fa n s, a n d some have formed QUARTZ BRECCIA a long fa u l t zones. Breccias may from Texas-fragments cemented by silica. be barely consolidated or tightly cemented, depe n d i n g o n their age and on conditions of forma­ tio n . Com m o n l y they are formed c lose to the point of origin of the fragments. 1 28

BOG I R O N O R E ( L I M O N I T E ) Mich i g a n

O O L I T I C H EM A T I T E C l i n ton, N . Y .

C H EM I C ALLY FORMED sed i m enta ry rocks a re per h a ps

the most i m porta nt commercia l ly. Some l i mesto nes are precip itated c h e m ica l ly from sea water. An hydrite, gyp­ sum, a n d h a l ite ( p p. 66-69) form d e posits large enough to be considered chemical sedimentary rocks as w e l l as m i n erals. They are often resid ues from sea water, which contains a b o u t 3 Yz l bs. of chemica l solids i n every 1 00 lbs. of water. Such d eposits genera l l y i n d icate an arid c l i mate at the time of their formation . Other sed i m e n ta ry rocks a n d fuels a re formed through bioc h e m ica l action, a n d of these coa l a n d o i l ( p p . 1 421 45) a re the best known. Bacteria may a i d i n the forma­ tion of iron d eposits in swa m ps a n d s h a l low la kes, and may be i n part responsible for the g reat I ron Range d e pos­ its. Biochem ica l action may account for the precip itation of m a n g a n ese a lso. D iatomaceous earth is a fine deposit of m icroscopic p l a n t ske leto n s-forming large, p u r e de­ posits of s i l ica.

D I ATOMAC EOUS EARTH Maryland

Arrowheads fou n d b u ried offer evid e n ce of human l ife. A t left, an a ncient folsom point from N ew Mexico. At right, m a r i n e fossils fou n d along Lake C h a m p l a i n , N . Y., s h o w that t h i s l a ke was once a n a r m o f the sea.

FOSSILS a re the re m a i ns, pri nts, or other i n d ications of former p l a n t or a n i m a l l ife found natura l l y b u ried in rock. World-wide stud ies over the past century i n d icate that the o l d e r the rocks, the s i m p l e r the types of plant and a n i m a l fossi ls fou n d i n t h e m . The fossils h a v e therefore b e e n used to esta b l i s h the age of the rock w h i c h e n c loses them. Fos­ s i l s show that many thousa nds of kinds of p l a nts a n d ani­ m a ls, com m o n i n the past, n o longer exist, and that most of those l iving today rese m b l e stro n g l y the fossil forms found i n relatively recent rocks. In a d d ition to te l l ing the deta i l s of l ife i n the past a n d the story o f such u n i q u e a n i m a l s a s g i a n t d i n osa urs a n d tita notheres, fossils a lso te l l of past c l i m ates. C o l o n ia l cor­ a ls i n Green l a n d rocks attest to warmer cond ition s i n the past than today, and i m prints of fi r and spruce in uncon­ s o l idated c lays near the surface record the penetration of g lacia l cold far to the south. Fossils are a lso used to de­ te r m i n e the m a r i n e or fresh-water origin of rocks. The occurrence of fossils is both ra re a n d com m o n . O n l y a tiny fraction of the tota l n um b e r o f living things has ever been p reserved as fossils, a n d yet certa i n l ayers of rock o r strata are made a l most entirely of shel ls, teeth , p l a n t rema ins, a n d e v e n of b o n e .

1 30

FOSS I L S are preserved in m a ny ways. The s i m p lest is the intact preservation of the h a rd pa rts of a p lant or a n a n i m a l, as i l l ustrated o n p. 1 30. Wood, bone, teeth, a n d o t h e r h a r d pa rts a re p reserved in­ tact for relatively short periods. In a nother type of fossi l ization , b uried p l a n t or a n i m a l materia ls d ecom pose, leaving a residua l fi l m o f carbon b e h i n d . T h i s m a y m a r k the form of a l e a f or o f some simple a n i m a l . On a larger sca l e t h i s process is responsi ble for o u r great d eposits of coa l . Sometimes b u ried material is g ra d u a l ly r e p l a ced by s i l ica a n d o t h e r materia l l i ke calcite, dolo­ m ite, or pyrite from solutions w h ic h permeate the rock in a p rocess called petrifa ctio n . These re p l ace­ ments form a n other very common type of foss i l . Proba b ly the m ost specta c u l a r of a l l replacements is that of wood by agate or o p a l as a result of the ac­ tion of hot, s i l ica-bearing waters. This forms petrified wood . The re­ placement m ay b e so m i n ute a n d complete that even t h e deta i l s of ce l l u l a r structure a re p reserved . The best-known exa m ples a re p reserved i n the Petrifi e d Forest Natio n a l Park i n Arizo n a .

C A R BO N I Z E D F E R N L EAF I l l in ois PET R I F I E D WOOD Arizona

structu re ( e n l a rge d )

CAST OF SHELL i n pyrite western Illinois

1 31

MOLDS A N D CASTS are very

footstep

i m p ression

B RAC H I OPOD

northwest O h io

north e r n O h i o

common fossi l forms. They a re im­ pressions, and so d iffer from intact preservation and re placements. A footprint, as that of a d i nosa ur, is a good exa m p l e of a m o l d . The i m ­ pression left i n soft m u d o r s i l t may harden before more sed i m e n t fi l ls it i n a n d provides mate r i a l for a new layer of rock. If the sediment later consol idates a n d the rock is eventu a l l y broken open, t h e orig­ inal i m print will b e fou n d below, and fi l l i n g it will be a cast of the u n derside of the d i n osaur's foot. When shells are b u ried in sa n d or mud, a m o l d o f the outer surface of the she l l is form e d . Percolating waters may dissolve the she l l mate­ ria l co m p l etely, a n d the m o l d w i l l t h e n be t h e foss i l record . Later, per­ colating waters may refi l l the cav­ ity with calcium carbonate or sil ica, form i n g a cast which will on its outer s u rface comp lete l y d u p l icate the extern a l form of the she l l . Pa leontology, t h e stu d y of pl a nt a nd ani mal fossils a n d their h is­ tories, is an i m porta nt a n d exciti n g b r a n c h of t h e science o f geology. The study of sma l l foss i l forms (wh i c h are k n own as m icrofossils) has re­ cently yielded a g reat dea l of n ew i nformati o n .

M E TAMO R P H IC ROCKS Meta m o r p h i c rocks a re rocks w hi ch have been changed. C h a nges m ay be barely visible, o r may be so g reat that it is i m possible to determine what the orig i n a l rock o n ce was. A l l k i n d s of rocks can be m eta morphosed-se d i m e n ­ ta ry, i g n eous, a n d other meta m o r p h i c rocks. The changes usua l ly bring about a new c r ysta l l i ne structure, the for­ mation of new m i n era ls, a n d sometimes a coarse n i n g of texture. Meta morph ism resu lts from h eat, pressure, or permea­ tion by other su bsta n ces. Pressu re a n d heat i n c rease with d e pth i n the ea rth 's crust (A, in the i l l ustration a bove) a n d m a y a lso result from crusta l movements (B) o r igneous a ctivity (C). Rocks m a y be permeated by g a ses or fl u ids from igneous m a teri a l (D) or by the perco lating of m i n e r a l ­ bearing g r o u n d-water. 1 33

SIMPLE METAMO R P H I C ROCKS is a conve n i e nt term

a p p l ied to rocks formed by the d irect a l teration of sedi­ mentary rocks where the cha nges are m a i n ly recrysta l ­ l ization . Few, if a n y , n e w m i n e r a l s a re formed. S o m e of these rocks show para l lel structures; others do not. S late resu lts from metamorph ism of sha le, and often traces of the orig i n a l bedd i n g can be seen. S late is fre­ q uently of a b l ue-gray color but may be g reen, red, or brow n . It breaks easily al ong a flat cleavage plane a n d c a n b e s p l it into s heets used f o r roofi n g or flagstones. Sometimes s l ate s h ows fo l d i n g and wri n k l i n g . Marbles a r e recrysta l l ized l i m estones, norm a l l y wh ite, but often tinted by iron oxide, carbon, o r serpentine to attractive shades of yel l ow, brown, g reen, or b lack. Lime­ stones a n d dolom itic limestones may b e s l i g htly a ltered by perco lating waters and a re often ca l l ed m a r b l es, but true m a rb l es a re the result of meta morphism involving heat and pressure. Seco ndary minerals may form and crysta ls may s h ow d istortio n . Marbles d o not often develop the para l l e l b a n d i n g and m ineral a rra ngement seen i n slates and sch ists. Quartzites a re usua l l y meta m orphosed sandstones which have recrysta l l ized so that, i n brea k i n g , t h ey break t h ro u g h the q u a rtz g rains instea d of throug h the cement, a s i n sandston es. The gra i n structure in q u a rtzite is not nearly as clear as in sandston es. Qua rtzite, l ike marble, is a m a ssive metamorphic rock, very h a rd a n d toug h . Hornfels a r e c l ays o r shales which have been meta­ morphosed th roug h the action of heat from nearby ig­ neous rocks. The h a rd, rec rysta l l ized rock may reta i n its sedimentary structure, but garn et and other secondary m inerals may form. The color is usua lly dark; the rock is spotted o r banded, a n d may be conf used with basa lt, espec i a l ly along contacts. 1 34

G RAY SLATE Pen nsylva n i a

New York

WHITE MARBLE Georgia

H O R N F ELS H a rtman n sd orf, Saxony

Q UARTZ I T E D e l l Rap i d s, S . D a k .

1 35

PHYLLITES A N D SC H I STS represen t the more h ig h ly

m eta morphosed rocks. P hyl l ite provides the transition, being m o re metamorphosed than s late but less than schists. F i n e g ra i n s of m ica g ive it a s i l ky l u ster. T h e schists are coa rser than phyl l ite, with a consid erable a m o u n t of mica or othe r secondary minerals. They b rea k i n a wavy, u n even surfa ce; this property is c a l l e d schistosity. Sch ists are n a m ed for their most cha racteristic m i n e ra l : M i c a Sch ist i s usua l ly a h i g h ly meta m o r p h osed shale com posed m a i n ly of m a ny sma l l fl a kes of m ica, o r iented rou g h l y para l le l , and q ua rtz. Texture varies from fine to coa rse, and either sta urol ite o r g a rnet m ay b e p resent. Hornblende Sch ist is m a i n ly h o r n b lende and q ua rtz. It is dark i n color, and w h i l e the minerals have a para l lel orientation, h o r n b lende schist does not break c l ea n ly. C h l o rite Sch ist conta in s c h l orite a s a meta m orphic mineral instead of mica; t h is gives it a greenish color. It has typica l sch ist orientatio n . Quartz Schist forms o n further meta morphism o f i m ­ p u re q uartzite. Muscovite m ica usua l ly develops as a seco n d a ry m in e r a l , a n d p a ra l l e l structures a lso form. light-colored. M I N E R A LS

OF

M E TA M OR P H I C

ROCKS

The fo l l ow i n g m i n erals are com monly fou n d i n meta m o r p h i c rocks. Actinolite Ch lorite Diopside Feldspars Garnets

Graphite Hornblende

1 36

in schists, gneiss and quartzite (p. 1 00) in phy l l ites and schists (p. 1 06) in marbles (p. 1 0 1 ) m a i n l y from igneous contacts (p. 98) nearly a l l kindsi n s c h i sts, marble� a n d phy l l ites (p. 1 04) in some s�h ists and marble (p. 62) i n metamorphosed basic rocks (p. 1 00)

Kyanite

i n sch ists (p. 48)

M icas

m u scovi te, biotite, and ph logopite i n schists, gneiss, a n d marbles ( p . 96)

Olivine

i n marbles ( p . 1 06) in schists, gneiss, a n d q u a rtzite (p. 76)

Q u a rtz Serpentine and talc Staurolite

(p. 74) i n marbles, soapstones, and schists ( p p . 74 and 1 07) in schists (p. 1 08 )

Page n u mbers i n dicate i l l ustrations .

GARN ET-M I C A SC H I ST New Yor k

H O R N B L E N D E SC H I ST Lingoutte, Vosges

C H LO R I T E SC H I ST C hester, Vermont

Q UARTZ SC H I ST Pen n sylvania

1 37

M U SCOVITE G N E I SS N asse n g r u b , Bohemia

G RA N I T E G N E I SS Bristenstock, Switzerland

(pronounced n ice) may be simply metamor­ p hosed gran ite, or a far m o re com p l ex rock with possibly four o r five d ifferent o rigins, either igneous or sed i m e n ­ tary. I t may a lso include meta morphic rocks w h i c h a re i n ­ vaded by ig n eous materia ls s o t h a t the r o c k becomes a complex m ixture (mig matite). Schists are often invaded i n this way, producing rocks which conta i n more feldspar and q ua rtz than o rd i n a ry schists. The new m i n erals a re often in sma l l l e n s l ike intrusions. Gneiss is h a rd to defi n e or describe because it is so va ried. I n ge nera l, i t is a coarse-textured rock with the minerals in para l l e l streaks o r b a nds, but lacking sch istosity. It is re latively rich in feldspar and usua l ly contains mica or one of the other da rk, rock-forming m i nerals. Gneiss is c lassified by its most conspicuous m i n era l or a ccording to its orig i n or structures. C h a ra cteristics a re usua l ly better seen in the field than in h a n d specimens. G N E I SS

1 38

HORNBLE NDE G N E ISS Stengerts, Bavaria

I NJ ECT I O N G N E I S S Sewen, Vosges Mts., F ro nce

Muscovite G n eiss is o n e of the most c o m m o n kin ds, with a pa l e sa lt-a n d -pepper a p pearance, though biotite m ica is com m o n i n gneiss a lso. W h i l e the n a m e g ives n o c l u e as t o t h e origin, m u scovite a n d biotite g neisses may form from h ig h ly meta m orph osed, shaly sed i m e nts. Granite Gneiss is n a m e d to i n d i cate that it is a meta m o r p h osed g r a n ite, though this origin is d iffi c u l t to esta b l ish beca use of the process of g ra n itization ( p . 1 40). Gran ite g n eiss is rich i n feldspars. The m ica o r h o r n b l e n d e i n it is a r r a n g e d i n pa ra l le l b a n d s . Hornblende G n eiss is a dark rock, m u c h d a rker than biotite g n eiss, i n which para l l e l-oriented hornblende re­ places m ica. It is proba bly the end result i n the m eta­ morphosis of basic igneous rocks. I n jection Gneiss is g neiss which has been permeated by igneous materia l s d uring metamorphism. like sch ists which are thus a ltered, it is a lso known as m i g matite.

1 39

c

1 40

GRANITIZAT I O N is a process in w h ic h some form of i g n eo u s mate­ ria l or a n other invades sedimenta ry or metamorphic rock, producing m ixtures w hi ch eventua l l y a lter the rock so that i n texture a n d compo­ sition it becomes l ike g ra n ite. This p rocess may be associated with g reat bathol iths o r it may originate with materia ls com ing from an un­ known depth i n the crust of the earth. The invasion may not even involve gases or l i q u i d s as we or­ d i narily know them . Gradations of rock from g ra n ite to g n e iss over wide areas is evi dence for at least one form of gran itiza tio n . O n e exam ple o f the process wou l d be the invasion of g neiss (A) by solutions conta i n i n g q u a rtz a n d feldspar t h a t sepa rate the g neiss a l o n g pa ra l l e l ba nds. In a later stage (B) some pa rts of the g neiss are tra nsformed w h i l e others reta in their orig i n a l stru cture. As gran it­ ization contin ues, the form a n d structure o f t h e g n e iss m i nerals change (C), though traces of the para l le l arra n g e m ent sti l l rem a i n . Fina l ly the orig i n a l r o c k is com­ p lete ly a bsorbed, and the resulting rock shows n o traces at a l l of the g n eiss. I n structu re a n d com posi­ tion, it is gran ite.

WORLD PRODUCTION OF ESSENTIAL M I N E RALS

N . America

S . America

Africa Asia Au stra l i a Ocea n i a Production r a n k (including s o m e estimates)

R O C K S AND M INE RA LS IN DAI L Y USE Rocks a n d m i n era l s are the basis of o u r civil izatio n . For the l ife we l ive today we m ust have meta l l ic a n d non­ meta l lic o res, t h e fuels, a n d the construction materia ls such a s· cements, c lays, sand, g rave l, a n d b u i l d i n g stones. Then there is the soil, perhaps the m ost va l u a b l e rock of a l l . Sand, c l ays, road rock, and so i l have a low va l u e per ton compared to meta l l ic ores, but because of the a m o u n ts used their overa l l va l u e is enormous. Since ores have been d iscussed e a r l i e r, this section deals m a i n ly with fuels, soi ls, and construction materia ls. Much of t h e tro u b l e between nations can be traced to the fact that t h e rocks, m i n era ls, and fuels are not eq u a l l y d istrib uted o v e r the e a rth. S o m e nations h a v e ; others have not. Blood has been shed over gold, si lver, iron, coa l, o i l , a n d u ra n i u m . T h i s is sti l l a critica l matter f o r u s a l l . 1 41

BITUMINOUS Pen nsylva nia

COAL is the fuel which made the i n d u stria l revo l ution

possible. About a b i l l ion a n d a half ton s a re sti l l m i ned a n n ua l ly (500 m i l lion tons i n the U n ited States) . Coal is an organic sed imenta ry rock consisti n g of the a ltered re­ m a i n s of p l a nts. It is formed by a slow series of c h a n ges m a rked by a loss of water and volatile su bsta nces and a corresponding in crease in the a mount of "fixed carbon . " Coa l is classified by t h e rel ative a m o u n t o f these three g roups of materials. Peat, which contains a bout 80 per cent m o isture, is not consid ered a form of coa l . Lign ite, the lowest ra n k or kind of coa l, has a heat­ i n g va lue of 7,400 Br itish Therma l U n its (B.T. U . ) . It is b rown i n color and breaks down into powdered o r fl aky fragments when stored. I t burns with a smoky fl a me. Bitu m i nous or soft coa l s are black coals which often have a cubic fracture and a d u l l l uster. They yield from 9,700 to 1 5,400 B.T. U . and tota l 90 per cent of the coa l m i ned. The higher grades of bituminous coa l store we l l a n d burn with a n a l most smokeless fl am e.

C H EM I CAL COMPOSITION OF COALS

- 1 00%

- 50

l i g n i te

1 '-----' ...__ _ __. 1 ____. ....__....;..;o.<

c-.....- _

subbituminous bituminous

anth racite

semibituminous

semia n t h r a c i te

v o l a t i l e matter

0

- m o i sture

Anthracite or h a rd coal is hard a n d d urable. It stores w e l l a n d burns with a very short smoke less fl a m e . Anthracite has a conchoida l fracture a n d a b lack s h i n y luster-som etimes iridescent. It forms w h e n fo l d i n g o r metamorph ism d r ives a larger a m o u n t o f volatile matter out of soft coal than wou l d otherwise be l ost. Most coa l s i n eastern a n d centra l U n ited States were formed d u r i n g the Pennsylva n ia n period when a warm c l i­ mate favored the rapid g rowth of fe r n l ike p l a nts. The coa l s of western U n ited States were formed many m i l l i o n s of years later. The coa l-bearing rocks are so metimes thousa nds of feet thick, with laye rs of coa l u p to 1 00 feet thick lying between layers of sa n dstones a n d s h a l es. The world's reserves of coal are very roug h l y estimated at a tota l of about seven tri l l ion ton s, of which over h a l f is i n North America. Not all of these reserves are usa b l e at the present price of coa l.

1 43

or u pward folds provide trap s for o i l a n d gas. Occasion a l ly the su rface patte rn i n d icates underlying structures. ANT I C L I N E S

m a r k movement along breaks i n the earth's crust. Oil may seep to the su rface or accu­ m u late a l o n g or a g ainst them.

FAULTS

PETROLEUM is the proper name for what m ost people ca l l o i l . It is a comp lex mixtu re of compounds of carbon and hydrogen, for which new uses are consta ntly being found. The commercia l production of petro leum began only a century ago. Now the U n ited States prod uces over two b i l l io n barrels a year a nd im ports oil i n addition to this. Nearly a l l interna l com bustion eng ines depend o n petro leum fuels a n d l u brica nts. . Petro leum is of marine origin and probably represents the remains of microscopic pla nts which settled i n the sand and mud of s h a l low bays. Deposits of oil bearing sands a n d sha les are plentifu l, but fo lding, faulting, o r o t h e r action i n the sed imenta ry strata (as i l l ustrated a bove) was necessa ry to form the structures for the accum u lation of the petro l eum. Such accumu lations are not u n derground . a sphalt paraffin lakes of o i l , but a re areas where b ase base the spaces between sa n d g rains or the pores i n carbonate rocks are satu rated with petro l e u m .

DOMES, pushing up through G u lf C oost sediments and deforming them, make suit­ able structu res to trap o i l .

SALT

Oil m a y b e confined w h e r e tilted l a y e r s h ave been worn down a n d later h ori­ zontal layers d eposited o n them. U N CO N FORM I T I ES

The most va l ued o i l s have a paraffin base-that is, the heavier "chain" type chemica l s are those of para ffi n . Another form of petro leum has a n asphalt b a s e a n d i s richer i n "ri n g " type chem icals. M a n y we l ls y i e l d a m ix­ ture of both t h ese types, and chem ica l l y the oils conta i n m a n y com p lex hydrocarbon compounds. O n o n e hand, petro leum compounds grade off i nto natura l g a s (p. 1 47). On the other, they g rade into the solid bitu m e n s a n d natura l aspha lt. Because of its g reat va lue, petro leum has sti m u lated more geologic exploration and research than any other minera l or rock. Petro leum su rveys extend i nto w i l der­ n ess areas and even out to sea. Treme n dous reserves which ca n be recovered economica l l y have been d iscovered ; i n the U n ited States a l o n e these amount to some 30 b i l l io n ba rrels. As a by-prod uct of petro l e u m re­ search our knowledge of sedimen­ tary rocks a n d of their structures has been g reatly i ncreased. 1 45

OIL SHALE contains solid hydro­ carbons m ixed with p l a n t remains. Extensive deposits of g ray, brown, o r b lack oil s h a l e a re fou n d in the Green River formation of Co lorado and i n Uta h , Wyo ming, and West­ ern Canada. Oil sha le h as been mined and used for some time i n Scot l a n d . I n the U n ited States i t cannot com pete w i t h . o u r r i c h o i l O i l shale with " p o o l s . " S h o u l d o u r r i c h e r d eposits fossil fish Wyom i n g become dep l eted, we have we l l over 1 00 b i l l ion barrels o f oil locked u p i n o i l sha les. During World War I I a n experimenta l p lant successfu l l y m a d e o i l from oil sha le. A ton of average oil shale, u pon h eati ng, yields a bout 25 gal­ lons of petro leum, nearly 1 0,000 cubic feet of n atural gas a n d am­ monium compounds. It is certa in that folding and oth er crusta l m ovements produced m ost ohhe traps in w h ic h o i l acc u m u l ated . The oil and gas a pparently m i g rated from a source rock thro u g h the porous sa nds until it was trapped against an im p ervious surface a n d slowly accu m u lated . Without these crustar tra ps petro leum may rem a i n d istributed in sha l es a n d 'sa nds, too d iffuse to be p rod uced eco nom ica l ly at present prices. Oil s h a l es and a lso o i l sa nds contain h uge reserves of solid hydrocarbons, fro m which oil can be made. How they will be util ized is, at the present moment, sti l l a n o pen q u estio n .

1 46

NAT U RAL GAS is fo u n d with petro leum, though some oil fields have very l itt l e gas a n d some gas fields yield n o commercia l oil. Chem ica l ly, natura l gas is a m ix­ ture of the l i g hter chemicals fou n d in petroleum-ma i n ly metha n e with buta n e, propa ne, and other gases. Carbon d ioxide, n itrogen, hydrogen sulfide and even h e l i u m may be water water present a lso. Production of natura l gas in the U n ited States averages about n i n e tri l l ion c u b ic feet a n n ua l ly. Reserves are enormous. Over 75 per cent of natura l gas g oes i nto i n d ustria l uses. Some is l i q u efied as bottled gas, and n atura l gaso l i n e is an im­ WELL Fl E L D p ro d u c i n g porta nt by-prod uct. From 1 Y2 to 2 gas f r o m t h e u p p e r zone, g a l lons of g a so l i n e may be ob­ o i l and gas from the mid­ tained from 1 000 cubic feet of dle zone, and oil below. natura l gas. N atura l gas gaso l i n e is produced at the rate of over 5 b i l l io n g a l lons a year, accounting for nearly h a l f of a l l U . S . gaso l i n e . Com pression p l a nts at t h e we l l ­ heads extract t h e gaso l i n e from t h e "wet" gas. Over a q uarter of a m i l l i o n m i les of pipel ines, some m o re than a thousa n d m i les long, carry natural gas a n d petro l e u m from we l l s to i n d ustr i a l centers a n d c ities. I n former times natura l gas pres­ sure o n a pool of oil was freq uent­ ly a l lowed to cause a "gusher. " When this h a p pened, a jet of o i l w a s s h o t severa l h u n d red feet into the air and wasted.

1 47

SOILS are those farmed i n p l a ce by the g r a d u a l d e c a y of parent materi a l . W h e n cut through t h e y s h o w a g rad u a l transition from fresh r o c k u p to d ecayed rock to su bsoil a n d top­ soil. Resi d u a l soils u s u a l l y form slowly. The deepening soil layer protects the rock beneath from further chemical action. Types of res i d u a l soils depend on the rock from which they form, cli mate, and other factors. RESI DUAL

SO I L is the best k n own, most complex rock a n d , fortu­

nate ly, one w h ich has been stud ied a l o n g time. The physica l a n d chem ica l weathering of surface rock ( parent materia l) with the a dd ition of org a n ic material , forms soi l . Pla nts a n d a n im a l s (especia l l y microscopic forms) contribute greatly to soil fo rmation, a s d o c l imate, vege­ tation, time, s l ope, and drainage. The result of centuries of a ctivity is a soil m a ntle from a few i n c hes to a h u n d red feet thick, though the average depth of so i l is o n l y a foot o r so. Since most l ife depends o n soi ls, they s h o u l d be p re­ served and ski l lf u l l y managed. o re de­ veloped on p a re n t material that has bee n moved by w i n d , water, or ice. H u g e deposits of wind­ blown s i l t serve a s the parent material fo r the loess soils i n the western prai ries. In t h e M issis­ sippi v a l l ey and a l o n g western streams are deposits of water­ borne a l l uvial materials on which some very rich so i l s have fo rmed. I n north ern states g l a c i a l d e bris is often the p a rent material. TRANSPORTE D SOI L S

TR OPI CAL R E D S O I L S o re well· developed, well-drained soils re­ sulting from the deep leaching action of much rai n a n d the chemical action of worm air. These may be resi d u a l soils of great thickness. The leach i n g and oxidation make poor soil which may be e x h a u sted after o few years of cu ltivati o n . The fo i l of the Mayan civil i zations h a s been attributed to soil e x h a u stio n .

So i l s may be c l a ssified in a half dozen ways, acco rding to various properties. They may be classified on the basis of texture (size of particle), as c layey, si l ty, o r sandy. Other c l assifications have been based o n col or, parent materia l , type of crop ra ised , a n d m a ny other bases. Most modern c lassifi cations beg in with t h ree great d ivisions o r zones ra n g i n g from im mature t o mature soils. Th ree ex­ a m p les of we l l -deve l o ped soils are ( 1 ) the tropica l red soils (true and mod ifi e d laterites), (2) the northern forest soils ( podsols) a n d their modifications, a n d (3) the grass­ land soi ls (chernozem and pra irie soi l s ) . F OREST SOILS il­ l ustrate different cond itions from those a bove. These g ray soils form u n d e r beds of spruce, pi ne, and fi r needles which a re acid in composition and decoy slowly. The organic and i n o r g a n i c ma­ terials mix poorly. Many of these soils of cooler reg ions have not been a l tered e n o u g h to make them good produc e rs witho u t spe­ cial h a n d l i n g . NORTHERN

I llinois

C LAY was used by prim itive men to make pottery not

long after they fi rst began to use sto nes a s too ls a n d wea pons. After centuries o f service, clay is sti l l essentia l in many i n d ustries. About 35 m i l l io n tons are mined a n ­ n u a l l y a n d a re used i n bricks, pottery, c h inawa re, ceramic p i pe, d r i l l i n g m uds, a n d for many other purposes. C lays a re a m ixture of sil ica, a l u m ina, and water. C lay particles are s m a l l - l ess than 0.000 1 inch. They stick together but are s l i p pery when moist. C lays may come from g ra n itic rocks, as a weathering product of the feldspa rs. They a lso form from weathered shales w h ic h came m a i n ly from clay m inera ls orig i n a l ly. Clay deposits form on lake bot­ toms and i n other q u iet water, sometimes with a n n u a l layers (va rves). O n e o f t h e c l a y m i n e ra l s is k a o l i n ( p . 49) .

electrica l insu lator

crushed limestone

crushed shale

PORTLA N D CEMENT is the best-know n i n g redient of a rtifi c i a l stone. It has largely replaced the older natura l cement or hyd ra u l i c l i mestone. When l im eston e conta i n i n g s i l ica a n d c l a y was burned, t h e l i m e t h a t formed would set u n der water, hence the name hydra u l i c l i m e. Now, l i m estone a n d s h a l e are crushed, dried, m ixed i n t h e correct pro portio ns, a n d ground t o a fi n e powd er. T h e powde red m ixture is burned i n a s l o p i n g rotary k i l n a t about 2700 ° F t o form a g lassy c l i n ker. The c l i n ker i s crushed, a sma l l a m o u n t o f gypsum is a dded, a n d the m ixture is reg rou n d to form cement. Over 200 m i l l ion barrels of Portland cement a re produced each year. Cement is m ixed with sand, crushed rock, a n d water to make concrete.

151

BENTONITE Wyom i n g

F U LLER'S EART H is clay or a s i lty clay materia l con­ ta i n i n g over h a lf s i l ica, valued for its decolorizing prop­ erties. F u l ler's earth absorbs dark orga n ic matter fro m fats, o i l s, a n d g reases. First used t o "fu l l " o r deg rease woo len c loth, f u l l er's earth is used to b leach m in era l a n d vegeta b l e o i l s . It has the greasy fee l of clay a n d usua l ly breaks up in water. Color varies from w h ite to yel low, b row n , and bl u e. B E N TO N I T E, fi rst deve loped, l ike f u l ler's earth, fo r b le a ch i n g , has t ur ned out to have even more i m porta n t uses. It is u s e d i n soaps and was hing c o m p o u n d s and i s a d d e d to cl ays to increase t h e i r p l asticity. Some benton ite, used a s an aid i n w e l l dri l l i n g, expands a n d sea l s off water-bearing sands. Other va rieties swe l l l itt le when wet. Benton ite is a lso used for paper fi l ler a n d i n ad­ hesives. It is a m ixture of at least two a l u m i n u m a n d mag ­ nesium silicate m i n era ls, and is usua l l y regarded as weathered volcanic ash.

1 52

SAND, G RAVEL, A N D C R U S H E D ROCK have a bout

the lowest va l u e per ton of a n y rock or m i n era l , yet a l l three a r e i n d i s pensable i n modern construction. Sa n d i n pla ces i s s o p l e ntif u l that i t shapes t h e l a n d scape, giving beaches a n d deserts a q u iet bea uty of their own. Sand is a size ·term; a lt h o u g h sa n d is usua l l y com posed largely of q u a rtz, p u re q ua rtz sand (used in the m a n ufacture of g lass) is rare. O n tro pica l shores, coral ( l ime) sa nds are com m o n . Gypsum sands make u p the snowy d u n es i n the Wh ite Sa nds Nationa l Monument. Other sa nds a re rich i n magnet ite, m o n az ite, g a r n et, i l m e n ite, a n d ruti le. Some are m i ned as ores. But it is common q u a rtz sa n d that h e l ps make o u r conc rete roads, brid ges, a n d b u i l d i ngs. Gravel, of g lacial o r stream origin, co n ta i n s larger pebb les from a q u a rter of a n inch u p, cobb l es, and even bo u l d e rs, i n a sa n d matrix. Washed, scree ned, and sorted, g rave l is used for fill a n d in con crete. limesto ne, basa lt, a n d gran ite a re crushed for road b u i l d i n g , ra i l road ba l last, a n d concrete work. 1 53

B U I L D I NG STO N ES a re th ose cut to size for b u i l d ings o r m o n u ments. Ornam enta l sto nes a re those used for fi n ishing o r decoration. Sto ne a lso has been used for sidewa l ks, curbing, and paving b locks. For b u i l d i n g use, ease of q uarrying , tra nspo rtation, d u rabi l ity. color, is famous for its beauty, strength , and d u rability -hence its wide use i n m o nu­ ments a n d b u i l d i n g s. G r a n i te to kes o h i g h polish a n d is resist­ ant to weath e r i n g . Its h a rd n ess a n d lock of b e d d i n g make q u a r· ryi n g difficult. G r a n ites for b u i l d ­ i n g u s e s are classified b y g r a i n size-with p r eference for fi n e­ grained rock. GRANITE

RED G R A N I T E W a u s a u , Wis.

TRAPROCK i s the q u a rrym a n ' s t e r m f o r d i a base, b a s a l t , o r g a b ­ bro. T h e s e h a rd , d u ra b l e rocks are l i m i ted in b u i l d i n g use be­ cause their iron m i nerals g i ve a rusty sta i n as they weather. Trap­ rock is exce l l e n t a s crushed rock and is widely used . Other i g n e­ o u s rocks-rhyolites a n d fel sites -are l oca l ly u se d as b u i l d i n g ston es.

C O A R S E GABBRO Aberdeen, Scotla n d i s relatively easy to q u a rry beca u se it is bedded. Many sandstones are attractive a n d d u rable, and once were very fashionable in Eastern cities. Po­ rous sa n d stone may not weather well a n d special treatment may be needed in cold regions. Other­ wise, sa n d stones make attractive b u i l d i n g sto nes. C o l o r and tex­ t u re ore variable .

SANDSTONE

1 54

. . C R A B O R C H A R O " STO N E T ennessee

weathering cha racteristics, a n d freedom from iron m i n ­ erals a re im porta nt. O f t h e b u i l d i n g stones which are sti l l widely used, the following genera l types are the best known . Many d ifferent kinds of marbles, l i mesto nes, a n d granites a r e used for varied effects. L I MESTONE from near Bedford i n central I n d i a n a is a well-known building stone, widely used for public b u i l d i n gs. Bedfo rd l i me­ stone is white, even-textu red a n d oolitic, someti mes packed with small fossils. I t is easily q u a rried and u n iform i n color. Many other kinds of l i m estones a re used fo r b u i l d i n g in m a n y pa rts of the U n ited Stales.

Swanton, Vt. MAR BLE fo r b u i ld i n g use also includes fi ne-g r a i n ed ornamental li mesto nes which are not true ma rbles. Marble is a classic stone, worked by scu l p tors as well as b u i l ders. I ta l i a n wh ite and Bel­ gian black m a r b l e a re fa mous. Marbles may a lso be p i n k, yel­ l ow, and brown. They are softer a n d less resistan t to weatheri ng than g r a n ites.

K i l l a rney, I re l a n d

is an u n usual b u i l d i n g stone u s e d p r i m a rily i n roofi n g a n d floori n g , b l ackboa rds, a n d e l ectrical switchboa rds. I t breaks along cleavage p l a nes i n large flat sheets. C o l o r varies from black to g reen and red . Slate is d u rable a n d attractive a s roofi n g a n d i n floors a n d patios. Most U.S. slate comes from Vermont, Mai ne, a n d P e n n sylvania.

SLATE

Bangor, P a .

1 55

M ORE INFORMAT I ON SOME SELECTED BOOKS to h e l p you further with rocks

and minerals are l isted be low. In addition, c h eck o n state p u b l ication s a n d those of the U.S. Geolog ica l Survey. A lso n ote the m a n y loca l g u ides to m i n e ra l hobbies a n d m i nera l loca l ities. S e e magazines f o r titles. Ford, William, DANA's TEXTBOOK OF MINERALOGY, John Wi ley, New York, 1 954. The sta ndard college text with description s of a l l species a n a mateur may fo n d . Tech n ical but thoroug h - a n adva nced book. Longwe l l and f l int, INTRODUCTION TO PHYSI CAL GEOLOGY, John Wiley, New York, 1 955. A beg i n n i n g geology text with append ices regard. ing the study of rocks and m i n e ra l s. Mcfa l l , Russe l l P., GEM HUNTER's GUIDE, Science & Mecha n ics Pub. Co., C h icago, 1 95 1 . A complete g u i d e to American gems o n d gem lo· calities, fo r col l ectors. Pough, frederick H., A f i ELD GUI D E TO R o C KS AND MINERALS, Houg hton Mifflin, Boston, 1 95 1 . You r next step is this excellent g uide with mi nerals clossifoed o n o chemical basis. Color p lates. S mith, Orsino C., IDENT I F I CAT ION AND QUALITAT I V E C H E M I CAL ANALYSIS OF MINERALS, Van N ostrand, New York, 1 953. A t a b u l a r guide of p hysica l o n d chemical tests. Advanced o n d technical, but comp l ete. Color p lates.

MAGAZINES

Earth Science GeoTi mes Horological J o u r n a l Lapidary J o u r n a l Rocks a n d Minerals

1 56

FOR

AMATEURS

Box 1 357, C hicago 90, I l l . 1 444 N Street, N .W. Washington, D . C . 20005 5250 Broadway Terrace, Oakland 1 B, C a l if. Box 398, Del Mar, Calif. Box 29, Peeksk i ll, N .Y.

bimonthly 8 times yearly monthly bimonthly b imonthly

MUSEUMS A N D EXH I B ITS will show you more kinds of

rocks a n d m i n erals than you will find on fi e l d trips. Use one to supplement the other. Some of the m useums with larger exhibits a re listed below. Arizona Holbrook:

Petrified

Forest

N a­

Michigan An n Arbor: U niversity of Michi­

tional Monument Museum; Tuc·

gan Mineralogy Museum; B loom­

son : U niversity of Arizona

field H i l l s : Cran b rook I n stitute of Science; Houghto n : Michig a n Col· lege of Mining and Tech nology

California Berkeley: University of California; Los Angeles: Los Angeles County Museum; San Diego: Natural His· tory Museum; San Francisco: Cal· ifornia State Division of Mines Museum; Santa Barbara: Santa Barbara Muse u m of Natural His· tory Colorado Boulder: University of Colorado Museum; Denver: Denver Museum of Natural H istory Connecticut New Hove n : Peabody Museum of Natural History Georgia Atla nta : Georgia State Museum I llinois Chicago: C hicago Natural History Museum; U r ba n a : U niversity of I l l i nois Museu m of Natura l H is· tory Indiana I ndianapolis: I ndiana Stole Mu­ seum Kansas Lawrence: Museum

U n iversity of

Kansas

Missouri Columbia: U n iversity of Missouri Museum; Jefferson City: Missouri Resources Museum Montana Butte : Monta n a School of Mines New Jersey Paterso n : Paterson Museum; Tren­ ton : New Je rsey State Museum New Mexico Socorro: New Mexico I nstitute of Mining and Technology New York Albany: New York State Museum; Buffalo: Buffalo Museum of Sci­ ence; New York: American Mu se­ u m of Natural H istory Ohio Cleve l a n d : Cleveland Museum of Natural History P en n sylv a nia

Philadelphia : Philadelphia Acad­ emy of

Natural Sciences; Pitts­

burgh : Carnegie Museum South Dakota Rapid C ity: South Da kota School af Mines and Technology Washington, D. C. U nited States National Museum

Louisiana Baton Rouge: State U n iversity De­ partment of Geology Museum

Ontario Ottawa: Notional Museu m of Ca nada; Toronto: Roya l Onta rio

Massachusetts Cambridge: H a rvard U niversity Mineralogital Museum; Spring­ field : Museum of Natural History

Museum of Geology and Miner­ alogy Quebec Montrea l : Redpath Museum

1 57

I N DEX Asterisks { * ) i n d icate i l l u strat i o n s .

0

o-

� = lE

;

"' ::l 0

�

::;

,... =

�

=

"'

i

!

�

�

"

�

� ,. � >E

Aa, * 1 1 9 Act i n o l i te [ a k -T I N - o - l i g h t] , 2 3 , * 1 00 Agate, * 1 2 , 80-*8 1 , *87, 1 3 1 A l abaster, 64, 67 A l b i te, *88, 98- *99 A le x a n d r i te, 84, *93 A l ma n d ite, 23, 1 04 A l u m i n a , 50 *84 A l u m i n u m , 1 9, *50, *141 Amazonite (AM - u h - z u h n i g h t ] , *88 Amethyst, 78 - * 79, *86 Am p h i b o l e [AMfy b o w l ] . * 75, 88, * 1 00 A n d esite, * 1 1 6 A n d ra d i te, * 1 05 A n g l e site, *35 A n h y d r i te, * 67, 1 29 A n o r t h i te, 98- *99 A n t ic l i n e, * 1 44 A n t i m o n y , 27, 28, 60 Apatite, 1 8 , 1 9, *73 A q u a m a r ine, *84 Arago n i te, *65, 89 Argentite, *38 Arkose, * 1 23 Arsenic, 60 Arsenopyrite, *20, *60 Asbestos, *75, *78 A u g i te [AW - j i te] . * 1 7, * 1 01 A u t u n ite, *55 Azurite, *33 Babbitt meta l , 45 B a rite, 1 9, * 72 B a s a l t [ b u h - SAWL T]. * 1 1 0, * 1 1 7 Batho l i th s , * 1 1 5 B a u x i te, 48- *49-50 Bead tests, *28 Bento n i te, * 1 52 Bery l , *57, *84 Bery l l i u m , 57

1 58

B i otite m i ca, *97, 1 39 B i smuth test, *27 B l ackjack, *46 B l a s t furnace, *42 B loodstone, * 8 7 B l owpipe tests, *26- *27 Borax, 1 9, *28, *70 Born ite, *32 Bou le, *92 Breccia [ B R E TC H - y u h ] , 1 1 8 , * 1 28 Bri l l i a n t cut, *90 B u i ld i n g stones, * 1 54 * 1 55 Ca l cite, * 63 - * 64 crysta l s , *6, * 1 6, *20 properties, 1 8 , 1 9 Carboloy, 44 Carbon, *62, *83 C a r n e l i a n , 80- * 8 1 , *87 Carnotite, * 55 , 56 Cassiterite, 1 9, *45 Casts, * 1 3 1 -* 1 32 Cement, Port l a n d , 1 5 1 Cerussite, *35 C habazite, 1 02 - * 1 03 C h a l cedony [ k a i - S E D u h - n i h ] . 80- B l , * B 7 C h a l cocite, *32 C h a l copyrite, 23, *32 C h a l k , 64, 1 26 C h e rt, *80 Ch lorite, * 1 06 C h lorite schi st, 1 36 - * 1 37 C h ro m ite, * 5 1 C h r o m i u m , 28, 5 1 C h r y sobery l , * 8 4 C h r y soco l l a , 3 1 , * 3 3 C h ry s o l i te , * 1 06 C h r y sopra se, 80- * 8 1 , *87 C h rysoti le, *75 C i n nabar, 1 9, *39 C i tri ne, 78-*79, *86 C l a y , *20, 1 24, * 1 50 C leavage, 20 C o a l , 89, * 1 4 1 - 1 43 Coba lt, 28, * 44

Coba l t i te, *44 C o leman ite, *70 C o l u m b i te, *57 C o n ch o i d a l fracture [ k o n - KOY-d u l l] , * 2 0 , *80, * 1 42 C o n cretion s , * 1 25 C o n g l omerates, * 1 28 C o n tact deposits, * 1 20 Copper, * 3 1 -33, * 1 41 tests, *27, *28, *29 C o q u i n a , * 1 26 C o ra l , *65 C o r u n d u m , 1 8 , 1 9, *4B m i n e r a l s , *84 C o ve l l i te, *32 "Crab Orc h a r d ' ' s t o n e , * 1 54 C ro c i d o l i te, 1 9, *75 Crocoite, * 5 1 C ryo l i te, * 48 C rysta l s , 1 4, 1 6- 1 7 C u b i c system crysta l s , * 1 6, C u prite, *33 C y a n i te, *48 Demantoid, *85· D e n d r i tes, *52- *53 D i a b a se, * 1 1 3 D i a m o n d , * 1 5, 1 8 , *83 s y n t h etic, 92- *93 D i atoms [ D I E - u h - to m s ] . * 8 2 , * 1 29 D i k es, * 1 1 4 Diopside, * 1 01 D i o r i te, * 1 1 0, * 1 1 3 D o l e r i te, * 1 1 3 Dolom ite, 64, *65, 1 27 D r u s y q u a rtz, *77 E lectr i c a l properties, 23 E m e r a l d , *90, *92- *93 Emery, *48 Enstatite, 2 3 , * 1 0 1 E p idote, * 1 7, * 1 08 E x t r u s i v e rocks, 1 1 0, * 1 1 6- * 1 1 9 F a i r y crosses, * 1 08 F a u lts, * 1 44

Fe ldspars, *98- *99 F e l s i te , * 1 1 0 F l a m e tests, *29 F l i nt, *8, *80 F l o s ferri, 65 F l u orescence, 22, 46, 55 F l uorite, 1 8, * 7 1 F o l so m point, * 1 30 Foo l ' s g o l d : see P y rite Foss i l s , * 1 30 - * 1 3 1 , * 1 46 Fracture, *20 Fran k l i n i te, *46 F u l ler ' s earth, * 1 52 F u s i b i l ity sca le, 23

Gabbro, * 1 1 0, * 1 1 3 , * 1 54 G a l e n a , * 1 6, *20, 30, *34, 47, 60 Garnet, *85, * 1 04 - * 1 05 i n m i ca s c h i st, 1 3 6 * 1 37 Gas, n a t u r a l , * 1 4 1 , * 1 47 Geiger counter, *24, *54-55 Gem cutt i n g , 90- 9 1 Gems, 83-91 synthetic, *92- *93 Geyserite, *82 G l a u berite, * 68 G n e i s s , * 1 38 - * 1 39 G o l d , 1 9, *36-*37 Granite, * 1 1 0, * 1 54 G r a n i t i z a t i o n , * 1 40 Graph i te, *62 Grossu l a r i te, * 1 04 G u m m i te, 55 Gypsum, *66 - * 67, 1 29, 1 4 1 , 1 53 properties, 1 8, 1 9

H a l i te [ H A L - ite) , * 1 6, 1 9, *68-69, 1 29 H a m mer, p l a stere r ' s , *4, * 1 0 Hardness, 1 8 Hematite, *35, *40, *89 H e m i morphite, *47 H e r k i mer d i a m o n d s , 76 H e x a g o n a l system c r y sta l s , * 1 6

H i dden ite, 8 5 H o r n b l e n d e , * 1 00, 1 36 - 1 37, 1 39 Hornfe l s , 1 3 4-* 1 35 H o r n stone, *80 H y a l ite, *82 I c e l a nd spar, *63 I g neous rocks, * 1 1 0 I l men ite, * 58 I ndex of refract i o n , 1 5 I n jection g n e i ss, * 1 39 I n terference patterns, *15 I n trusive rocks, 1 1 0 - 1 1 5 I ro n , *28, 40-*42, * 1 4 1 J a d e , *88 J ad e i te, * 1 3 , 88 J a sper, 80- * 8 1 , *87 J et, *89 Kao l i n , *49 Ker n i te, *70 K y a n i te, *48 Labradorite, *98 lacco l i ths, * 1 1 5 Lapi l l i , 1 1 9 Lapis-lazuli [LAP-issLAZ-you - l ie], *88 Lava, *6, 1 1 6 • * 1 1 9 Lead, *27, 34-35, * 1 -4 1 L e p i d o l i te [ le e - P I D-ol i g h t ) , 97 L i mestone, *6, * 1 26* 1 27, * 1 55 L i mon ite, *40 Lode, * 1 20 Lodestone, 23 L u ster, 2 1 Magnesite, * 59 Magnetism, 2 3 , 43 Mag netite, *40, 48, 58 M a l a c h i te, * 3 3 , *88 M a n g a nese, 28, 5 2 M a n g a n i te, 52 - * 53 Ma r b l e , 1 34- * 1 35, * 1 55 Marca s i te, * 4 1 Mercury, *39 Meta morphic rocks, * 1 33 - * 1 39

Meteorites, * 40, 1 0 1 Micas, *20, 96- *97, 1 36 Micro c l i n e, *88, 98- *99 M i g matite, 1 38 , 1 39 M i l l e r i te , *43 M o h s ' sca l e , 1 8 M o l d s , * 1 32 M o l y b d e n i te, * 56 M o l y b d e n u m , 28, 56 M o n a z ite, *57 M o n o c l i n i c system crysta l s , * 1 7 Moonsto n e , *88, 99 Morion [MO-ri h - u n ] , 78 - * 79 Moss agates, *52 Mud cracks, * 1 2 5 Muscovite, 96- *97 in qua rtz s c h i st, 1 36 properties, * 1 5, 1 9 Muscovite g n e i s s , * 1 38 - 1 39 N a tro l ite, 1 02 - * 1 03 N a tura l g a s , 1 4 1 , 1 47 N i cc o l ite, *43 N ic k e l , 28, *43 Obs i d i a n , *20, *89, * 1 1 0, * 1 1 6 O i l : see Petro l e u m O i l s h a l e , 1 46 O l igoc lase, 99 O l i v i ne , * 1 06 Onyx [ O N - i x ] , 64, 8 0 - * 8 1 ' *87 Oo l i t i c l i mestones, * 1 26 Opa l , * 2 2 , *82, *86 Orpiment, *60 Orth o c l a se, 98 - *99 properties, 1 8 , 1 9 , 23 Orth o r h o m b i c s y stem crysta l s , * 1 7 P a h o e h oe [ p u h - H Oa y h oa y ) , * 1 1 9 P a i n tpots, 1 22 - * 1 23 Peacock ore, *32 Pea r l s , 88-89 Pecto l i te, 1 02 - * 1 03 Pegmatite, * 1 1 2 P e n t l a n d ite, 4 1 , 43 Peridot, * 1 06

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S a l t : see H a l ite So I t domes, * 1 45

1 60

S a l tpeter, *68 S a m a r s k i te, * 57 Sand, * 1 53 Sand stone, * 1 22 - * 1 23 , * 1 54 quartz content, 76 S a p p h i re, *84, *92 - '93 Sord, 80-8 1 , '87 Sardonyx, 80- ' 8 1 Sa t i n - s par, 64 Schee l i te, *22, * 56 Schi sts, 1 36, ' 1 37 S c h i stosity, 1 36 Scoria, * 1 1 0, 1 1 7 Scratch test, * 1 8 Sed i mentary rocks, ' 1 2 1 - ' 1 29 Septa r i a n co ncretion, ' 1 25 Serpe n t i n e , 1 9, * 1 07 associations , 5 1 , 75 S h o les, ' 1 24, ' 1 46 S h e l l l i mestones, * 1 26 S i d e r i t e , 1 9, * 4 1 S i l ica, *76, 82 S i l icates, 95 S i l ls, * 1 1 4 S i lver, *38 S k u tterudite, * 44 S l a te, 1 34- " 1 35, ' 1 55 S m i t h s o n i te, * 47 Soapstone, 74 Sod i u m , t e s t , 1"29 So i l , * 1 48 - ' 1 49 Specific g r a v i t y , * 1 9 Spessa rtite, * 1 05 Spha lerite, ' 46 Spi n e l , 59, '85, '93 Spod u mene, * 1 3 , * 8 5 Sta u r o l ite, * 1 7, 1 9, ' 1 08 Steo t i te, * 74 Ste r l i n g s i l v e r , 38 Stibn ite, 23, '60 Sti l b i te, 1 9, 1 02 - * 1 03 Strea k , 21 Strontium, test, * 2 9 Sub l i mate, 26 S u l f u r , * 1 7, * 6 1 , 1 4 1 properties, 1 9, 23 tube test, *30 Syen i te, * 1 1 0, * 1 1 2 Synthetic gems, *92 - *93

Tole, 1 8, 1 9, * 74 T a n t a l ite, *57 T e l l u r i u m , 37 Tetr a g o n a l sy stem crysta l s , * 1 6 T h o r i u m , 57 T i g e r ' s eye, *78 Tin, * 45 T i ta n i u m, 28, 58 Topaz, 1 9, 23, '85 s y n t h e t i c, * 93 T o u r m a l i ne, * 2 3 , *93, *95 Traprock, * 1 54 Travertine, *64 Trem o l i te, 1 9 , ' 1 00 T r i c l i n i c system crysta l s , * 1 7 T r i p o l ite, * 8 2 Tube tests, *30 Tufa, 64, ' 1 27 T u n g sten, 22, 56 T u r q u o i se, '�- 8 9 T w i n n ed crysta l s , * 63, * 66, * 7 1 , * 1 08 U l trav i o l e t l i g h t , 2 2 , 77 U n co n f o r m i t i e s , * 1 45 U r a n i n i te, 1 9 , * 54 U r a n i u m, 2 2 , "28 , 54-55 U r a n o p h a ne, *55 U va ro v i te, * 1 05 V a n a d i n ite, * 56 V a n a d i u m , 2 8 , 55-56 Varves, 1 24, 1 50 Verd a n t i q ue, * 1 07 Ve r m i c u l i te, * 96 V o l c a n i c bombs, * 1 1 9 V o l c a n i c g l a s·s , *89 V o l canoes, * 1 1 8 W i l l e m i te , ' 2 2 , *46, *47 Wo lfra m i te, * 56 W o o d , p e t r i fi e d , * 1 3 1 Zeo l i te s , 1 02 - * 1 03 Z i n c , 26-27, 46-47 Z i n c b l e n de, * 46 Z i n ci te, 1 9 , * 46, 47 Z i rcon, * 1 6, 1 9, *85, *93

KK L L MM N J

ROCKS AND M I N ERALS A GOLDEN NATURE GUIDE

H E R B E R T S . Z I M , P h . D . , S c . D . , i n i t i ated t h e G o l d e n G u i d e S e r i e s a n d was b o t h a u t h o r a n d e d ­ i t o r f o r m a n y y e a r s . A u t h o r of s o m e n i n ety b o o k s a n d e d i t o r of a b o u t as m a n y , h e i s n o w A d j u n c t P r o f e s s o r a t t h e U n i v e r s i ty of M i a m i a n d E d u c a ­ t i o n a l C o n s u l t a n t to t h e A m e r i c a n F r i e n d s S e r v i c e C o m m ittee a n d oth e r o r g a n i z a t i o n s . H e w o r k s o n e d u c at i o n , p o p u l at i o n a n d e n v i ro n m e n t a l p r o b l e m s .

P A U L R . S H A F F E R , P h . D . , f o r m e r l y P rofesso r of

G e o l o g y at the U n i v e rs ity of I l l i n o i s , has w r itten many g e o l o g i c al p a p e rs f o r s c i e nt i f i c j o u rn a l s . H i"s acade m i c a n d i n d u s t r i a l work takes h i m i nto m o st

reg i o n s o f t h e U n ited States, studyi n g and c o l l e ct i n g .

RAY M O N D P E R L M A N i s a P rofes s o r of A rt at t h e U n i v e rs i ty of I l l i n o i s . H e h o l d s d e g rees i n f i n e a rts from t h at u n iversity, and is a M aste r of P rofes­ s i o n a l A rts from the A rt Center S c h o o l in

Los

A n g e l e s . He has d e s i g n e d and i l l u st rate d many books on science.