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