Rocks and Minerals

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THE HOW AND WHY WONDER BOOK OF

By Nelson W. Hyler

Illustrated by Kenyon Shannon

Edited under the supervision of Dr. Paul E. Blackwood

Washington, D. C.

Text and illustrations approved by Oakes A. White

Brooklyn Children's Museum Brooklyn, New York

N

LS

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I NTROD U C T I ON

In an age of rockets and missiles, the study of rocks and minerals is no less important- and in this colorful How and Why Wonder Book, we see why it is so important. We learn that our modern age of rockets would not even be possible without minerals from the earth's crust. We learn the answers to dozens of important questions about the earth's surface and the changes that take place in it.

Anyone who has ever picked up a rounded pebble, a curiously shaped rock or a sparkling gem and handled it with wonaer knows the urge to col­ lect. The chances are that almost everyone who has walked in a field, along a stream or in a park has pocketed a sample of rock or mineral to examine and enjoy later. What is it? How was it made? Is it valuable? This How and Why Wonder Book about rocks and minerals is useful because it helps to answer these and other questions. In addition, it tells how to start and how to organize a rock collection. It is a helpful guide for parents and children who want to study rocks together.

Scientists who study the earth's surface are called geologists, and this book will help children explore the big questions which geologists are study­ ing. It surely should take its place with the other How and Why Wonder Books on the library shelves of all science-minded young readers.

Paul E. Blackwood

Dr. Blackwood is a professional employee in the U. S. Office of Education. This book was edited by him in his private capacity and no official support or endorsement by the Office of Education is intended or should be inferred.

Library of Congress Catalog Card Number: 61-1514 ISBN: 0-448-05004-8 (WONDER EDITION) ISBN: 0-448-04003-4 (TRADE EDITION) ISBN: 0-448-03836-6 (LIBRARY EDITION)

1978 PRINTING

Copyriaht tC 1960, 1969 by Grosset & Dunlap, Inc.

All rillhts reserved under International and Pan-American Copyrillht Conventions. Published simultaneously in Canada. Printed in the United States of America.

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CONT ENTS

Page

THE WORLD OF ROCKS ROCK-FORMING MINERALS

AND MINERALS What are some of the rock-forming

What is our earth made of? 4 minerals? 32

LEARNING ABOUT OUR WORLD IDENTIFICATION OF ROCKS

Why do we study about rocks and AND MINERALS

minerals? 5 How do we begin to identify rocks

ROCKS and minerals? . 34

What is a rock? 6 How can you tell how hard a rock or

Are rocks found everywhere? 7 mineral is? 35

MINERALS THE SCALE OF HARDNESS

What is a mineral? 8 MINERALS

Where can you find minerals? 9 What are the hardness minerals? 36

VOLCANOES SIMPLE TESTS

What is an active volcano? 10 How can you tell what kind of rock

IGNEOUS ROCKS - ONE OF THE it is? 39

THREE BIG GROUPS OF ROCKS How can you test a rock or mineral for

What is an igneous rock? 12 weight? 39

Where do igneous rocks come from? 13

FOSSILS Are there many kinds of igneous

What is a fossil? 40

rocks? 14

Why do we study fossils? 4 1

ROCK QUARRIES

What is a quarry? 16 Where are fossils found? 42

EROSION RARE STONES

Does the earth wear out? 17 What makes a mineral a gem stone? 43

SEDIMENTARY ROCKS PUMICE

Are there rocks under the water? 18 What is pumice? 44

How are rocks made? 20 COAL

Where are sedimentary rocks found? 21 What is coal? 44

Are there many kinds of sedimentary ASBESTOS

rocks? 22 What is asbestos? 45

METAMORPHIC ROCKS

ICE Why do rocks have different shapes and

What is ice? 45

colors? 24

Where do metamorphic rocks come START A ROCK AND MINERAL

from? 25 COLLECTION

Are there many kinds of metamorphic How do you begin a rock and mineral

rocks? 26 collection? 46

CRYSTALS What will you need to collect rocks

What is a crystal? 28 and minerals? 47

How can you make a crystal? 29 How can you keep your rocks and

min-MINERAL FOODS erals? 47

Where does the salt we eat come from? 30 IDENTIFICATION CHART OF

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THE WORLD OF ROCKS

AND MINERALS

What is our earth made of?

ALMOST all of

J-\

the earth

-the hills, -the moun­ tains, the ground

itself - is made of rocks and minerals. There are many diff erent kinds, and

it would take a long time jus t to write

down all their names. Yet, most of the rocks and minerals on earth are very

com mon.

Sand is a common mineral. It is com­ mon b ecause it is found everywhere.

Water is another common mineral.

W e find it in the streams and in the

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nvers. It fills the lakes and the seas. M ost of the earth is covered with water. The great oceans of the world, together with the streams, rivers and lakes, cover

about three-fourths of the surface of the world.

M ix ed up in these wa ters are other minerals. W e cannot see them by look­

ing into the water, but they are there j ust the same. These minerals have been

dissolved in the water.

Water is very important because we cannot live without it. It helps to make

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L E ARN I NG A BO U T O U R

Why do we

study about

rocks and minerals?

W

world. It E LIVE in a wonderful Is full of

interesting things and it is fun to lea rn about things.

Almost all of our world - even the inside of the world - is made of roc ks and minerals. We study them to lea rn about our world.

Every day we use something ma de of rocks or minerals. But often they ha ve been changed. They do not look the

sa me.

Gla ss does not look like sa nd. Yet glass is made from s�nd. The ink that

printed the letters on this page wa s ma de from minerals. We study about rocks a nd minera ls to lea rn about the things we use every day.

Ma ny people ea rn their living by working with roc ks a nd minera ls, ma k­

ing them into many diff erent things we use. Some people ha ve fun just looking for and finding rocks. It is importa nt to learn about roc ks a nd minera ls so we can learn to live b etter.

We study about roc ks and minera ls to learn about our world, to lea rn about the things we use, a nd to lea rn to ea rn a livelihood.

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What is a rock?

RO CKS

ROCKS

made of min-a r e

erals. A few are made of j ust one mineral, but most of them are made of many minerals. There are many kinds of rocks.

Very small rocks are called sand.

Very small sand is like sugar or salt. The i ndividual grains are so small that

they are hard to see.

·

R ocks bigger than sand have . other names, like pebbles, or stones. Big r ocks are called b oulders. Some of them

may b e as b ig as a house.

Rocks ar e big and little. They have di ffer ent shapes and sizes. R ocks are sometimes round like a ball, or square lik e a b lock .

R ock s are of many colors. You can find r ed rocks, b lue r ocks and yellow r ocks. Often rocks are made of mix ed color s. W hen y ou look, you can find them of almost every color.

THE SEASHORE, AT LOW TIDE, SHOWING SAND, ROCKS OF DIFFERENT SIZES, AND ROCK CLIFFS IN THE BACKGROUND

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A STREAM SHOWING ROCKS WHICH HAVE BEEN SMOOTHED AND ROUNDED BY WATER FLOW

Are rocks

found everywhere?

R

O CK S a r e foun d alm ost

everywhere. The most comm on place is outdoor s on the groun d. Mo st o f the groun d is m ade up " of b ig an d little rocks.

Rocks are foun d at the seashore. Even the tin y pieces of san d are coun t­ less little ro cks that m ake up the b each. The waves of the ocean wash an d r oll the san d ar oun d.

Outdo ors yo u can fin d m an y rocks. Y ou can fin d r ocks in the hills, in the

valleys an d in river s an d stream s. The rocks in the river s an d str eam s are smoo th an d roun d. The water m oves alon g and pushes them ar ound .

The rocks then b ecom e smoo th an d roun d by r ubbin g arid b um pin g again st each other.

In this w ay sharp r ocks are b roken ,

into sm aller r oc ks an d in tim e ar e m ad e smo oth an d ro un d . Rocks ar e b ein g chan ged all the time b y movin g w ater .

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MINERALS ARE ALL AROUND US- AT HOME, IN SCHOOL AND OUTDOORS. THE KITCHEN IN YOUR HOME USUALLY HAS MANY THINGS MADE OF MINERALS.

MINERALS

What is

a mineral?

A

MI NERAL i s a chem -i cal e lemen t or a comb ina tion o f che mi cal elemen ts. Min ­ er al s are a ll a ro und us and they are ea sily fo und a lmo st e verywhere . In

fa ct, i t may be said th at any thing th at i s no t an animal or a vege tab le i s a m ineral .

Yo u sho uld be able to loo k aro und a s yo u read thi s boo k and see so me o f

the se mine ra ls. Can yo u see a window ? The gla ss i s a mineral . Can yo u see a d ish? Can yo u see any ki tchen po ts an d

pan s? The se and o ther ho use hol d ar ti -8

de s a re m ade o ut o f m ineral s, too . A go od par t o f yo ur woo den penci l i s m ade o f miner als. The part that m ake s the bl ack m ar k is m ade of gr aph­ i te - a miner al . Th e me tal par t that ho ld s the er ase r is m ade up o f mine rals,

too, as i s the pain t on the pe nci l. Almo st all m ine ral s are so lid s,, b ut w ater is a l iquid mineral . I t i s made up o f two chemi cal e lemen ts - o xygen

and hydrogen .

Some o ther miner al s are clay, ch al k and oil . Me tal s, such as iron, sil ver an d gol d are mine ral s, too . S cien ti sts ha ve fo un d abo ut 2,000 di ffe ren t spec imen s.

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Where can you

find minerals?

S

OM E m in er­als are foun d

on t o p o f t h e groun d. Others are dug up from un der the groun d.

M an y people go aroun d lookin g for m in erals. Prospectors are m en who look for valuab le m in erals. In m an y places they have foun d large deposits. Then a m in e m ay b e started, if en ough is foun d in on e place. The m in eral is then taken out of the m in e an d sold.

A m in e where iron is foun d is called an iron m in e an d the m in eral taken out

is named iron ore. The word " ore" usually refers to an y n atural m aterial which con tain s a valuab le m etal. A gold min e has gold ore _an d a lead m in e has lead ore.

In man y cases, m ore than on e kin d of ore is foun d together. Often, for example, silver an d lead ores are close together.

All min erals do n ot com e from m in es.

Som e of our im portan t m in erals com e from the sea. Salt is an im portan t m in ­ eral. Y ou use salt in your food. Salt is foun d b oth in the sea an d on the lan d .

OPEN PIT IRON MINE

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VOLCANOES

THE BEGINNING OF A VOLCANO What is an

active volcano?

AN

volcan o is AC TIVE

on e. that is said to b e " er uptin g." It shoots out steam, ash an d hot r ocks. Such a volcan o is wor k­ in g an d it is active.

M illion s of year s ago ther e wer e man y acti ve volcan oes. They wer e wor k­ in g in m an y places. Som e wer e wor kin g her e in Am er ica.

A vo lcano b egin s deep down in th e ear th, w her e i t is ver y hot. It is so ho t that the r ock has turn ed in to m agma -a n -am e for ver y hot r ock.

Deep in the ear th there is much hot 10

THE START OF A LITTLE VOLCANO

m agm a, which is som etim es pushed up­ war d b y pr essur e fr om the heavy rocks all ar oun d it. Fin ally the hot m agma r eaches the top of the gr oun d. H er e it br eaks a little cr ack or hole in the ear th.

Steam, ash es an d h ot r ocks com e out. Loud noises com e fr om it as the ro cks ar e b lo wn o ut. Th e ro cks p ile up ar oun d the hole an d the pi le b egin s to form a con e ab out the cr ack in the earth. The con e is m ade up of rock, ashes an d m aterial thrown out of the volcan o.

This is the b eginnin g of a li ttle vol­ can o. Da y after day i t wor ks an d gr ows.

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The ro cks an d ashes g ro w in to a big hill . Mo re ash es an d ho t ro cks com e o ut o f the hol e at the to p o f i t. Ano ther n am e fo r thi s hill is a vol cano .

Som etim es the vol cano po urs o ut lava. L ava i s very ho t an d i s m ade o f hot m el ted ro ck, whi ch i s al so call ed mol ten roc k.

The ol d vol cano has wo rked fo r m any y ears. It has b uil t a l arg e mo un ­

tain an d m ade som e sm all er hill s clo se by . The vol cano has turn ed th e fl at

lan d in to hills an d mo un tain s.

A DORMANT VOLCANO

Other vo lcano es have b een wo rking, too, helping to b uil d up the l an d.

Vo lcano es that wo rked m any million s o f y ears ago are no long er acti ve. Only

the hill s an d mo un tain s they b uil t long ago remain to tell us that they on ce exi sted.

Wh en a vo lcano has no t er upted for a long tim e, i t i s do rm an t. Thi s kin d o f vol cano i s kno wn to b e in acti ve. If i t is in acti ve fo r a very long time, i t m ay b e con si dered dead. Th en the vo lcano

is said to b e ex tin ct.

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I GN EO U S ROCKS -ONE OF

What is an

igneQus rock?

I

GNEOUS i s the name of on e of

t h e t h r ee b i g gro ups of roc ks . Igneo us roc ks were m ade in a s pecial w ay .

The wo rd i gne ous means m ade from . fi re or he at. The refo re, all i gne ous roc ks h ave been fo rmed b y he at.

Dee p down in the ea rth i t is very ho t.

The rocks an d mine ral s the re are ve ry hot. The he at h as hel ped to ch an ge these roc ks and mine ral s in to mol ten roc k, c alled ma gm a.

GRANITE

BASALT CLIFF

W he n the m agma c om es up to the surface of the e arth, i t c ools off and be come s hard . The cold magma, h ard­ ened in to roc k, i s called i gne ous roc k.

The re are many di fferen t kinds of i gne ­ o us roc ks, b ut a ll of them h ave co me from the magm a found dee p in the e arth.

S ometi me s the magma does no t ge t all the way up to the e arth's surface . It cools undernea th the gro un d, turning in to roc k before i t ge ts to the s urface . T his kind o f i gne ous roc k i s cailed

gr ani te .

Huge roc ks a re fo rmed under the gro und in thi s manne r. Some times the roc ks m ade in thi s w ay are se ver al miles lon g an d almos t as wi de and dee p.

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THE THREE

B I G

G RO U P S O.F

Where do

igneous rocks

come from?

A

n eo u s ro c k s i s GOOD place to f i n d ig ­

near o ld vo lcanoe s. The se ro cks we re made whe n the vo l­ canoe s we re still active. To day yo u can still fi nd the ro cks they made .

Many diffe re nt ki nds o f ro cks are fo und near the o ld vo lcanoe s. Lava is o ne . It i s a commo n ig neo us ro ck.

L ava in the fo rm o f mo lte n ro ck po urs o ut o f a crack in the side o f a vo lcano . It runs ste aming do wn the side o f the vo lcano and o ver e ve rythi ng i n

its path.

RIGHT: AN ERUPTING VOLCANO SHOWING MOLTEN ROCK AND LAVA FLOWING DOWN ITS SIDE. BELOW: IGNEOUS DUMP ROCK FROM VOLCANOES.

In time, the mo lten lava coo ls and harde ns, turni ng into ig neo us ro ck. The name, lava, can me an the mo lten ro ck o r eve n the co ld hard ro ck.

Lo ng ago the re were many vo lcanoe s i n the we ste rn state s and some in a fe w o f the e aste rn states. They we re active

fo r m any ye ars, throwi ng o ut ash es, cinders, ro cks and dust. Y ear after ye ar the y wo rked, b uilding the land h ig he r and highe r.

If yo u live in the West, yo u can still see whe re the volcanoe s o nce we re ac­ tive . To day they are ex ti nct. Aro und and abo ut the m yo u wi ll fi nd many ki nds of i gneo us ro cks.

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Are there

many kinds of

igneous rocks?

G

most common Ig-RANI T E i s o n e o f o u r

neous rocks, made deep under the ground.

Granite is made of quartz, feldspar and mica. These are all minerals . Quartz and feldspar are light-colored. They make granite a light-colored rock. The little bits of mica in granite make the dark spots.

Granite may be colored red, pink, yellow or brown. Often it is a mixture of colors in between.

DIORITE is an igneous rock. It is made like granite, but is much darker

in color. It is darker than granite be­

cause it has no white quartz in it.

Diorite is made of dark minerals -dark feldspars and hornblende.

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GRANITE

DIORITE

FELSITE rocks are made from fast­ cooling lava. The lava cools too fast to turn into granite or basalt. The lava cools too slowly to make obsidian, an­ other kind of igneous rock. It cools just right and turns into felsite.

Felsite rocks are usually made from light-colored lavas. These rocks are often colored light gray, green, yellow or even red.

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BASALT is a rock that comes from volcanoes. Sometimes the lava from a volcano is a very dark color. As this dark lava slowly cools, it turns into a black rock called basalt.

Basalt is a very useful igneous rock. It is crushed and sold to make many useful things. Basalt is used in side­ walks, buildings and roads, just like granite.

This kind of rock was formed in giant sheets when the ancient volcanoes poured out huge fl ows of lava that cooled faster than the granite-forming magmas.

INDIANS MADE THE TIPS OF THEIR SPEARS AND ARROWS OUT OF OBSIDIAN.

OBSIDIAN is another igneous rock made by volcanoes. W hen lava fl ows out of the volcano, it often cools very fast and f orms a rock called obsidian. This rock looks just like colored glass. It is really natural glass and is found

in many colors.

Indians found obsidian very useful.

They made the tips of their arrows and spears out of it. The way in which this rock breaks apart makes it easy to shape arrow and spear points.

Can you tell how the igneous rocks you have j ust read about were made?

Granite and diorite were formed when the m agma did not reach the sur­

face of the earth. This magma cooled very slowly deep under the earth's surface.

Basalt was made when the magma reached the surface. This magma came out of the earth and we call it lava. The lava cooled into basalt.

Felsite formed from faster cooling lava than basalt. But the fastest cool­ ing lava of all turned into glass. This natural glass we call obsidian.

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HEAVY CRANES ARE USED BY WORKERS IN QUARRIES TO LIFT BIG ROCKS . IN THIS GRANITE QUARRY, A MAN GUIDES THE MOVEMENT OF A ROCK WHICH HAS BEEN RAISED UP BY A CRANE.

ROCK QUARRIES

What is

a quarry?

A

QU ARRY is a larg e ope n

h ole in the g roun d

or the side of a hill. It is a place whe re roc ks and sto ne s are d ug o ut.

The re are many ki nds of rock quar­ ries. One kind will have g ranite rocks. Anothe r wi ll h ave sandstone and the re

are some quarrie s of marb le , too.

Big machi ne s he lp the worke rs take th e rock out of a g ranite quarry . Th e b ig rocks are use d to b ui ld m any th ing s, 16

b ut most of the time the b uilde rs nee d more smal l rocks th an b ig rocks.

Rock -crushi ng machi ne s take the b ig rocks and b reak the m i nto smalle r pie ces. The se sm all piece s o f bro ke n

rock are calle d crushe d rock or g rave l, wh ich is use d to b uild ne w roads.

Rock i s he avy and ex pe nsi ve to m ove a long way. There fore, we fi nd ro ck quarrie s c lose to big dtie s o r ne w ro ads whe re lots of crushe d rock is use d for construction purpose s.

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Does the

earth

wear out?

EROSION

V

OLCANOE S are land build­ ers. They help to m a k e t h e land higher. But the land does not stay built up. It keeps wearing away. Day after day and year after year, the wind and the water help to wear away the land.

The wind may blow dirt, sand and soil into a nearby stream. The stream carries the dirt, sand and soil to the sea. Day after day the earth is washed away by running water.

You may have seen a muddy stream or river. It was carrying the earth toward the sea. This is the way the wind and the water are taking away the earth.

N ot all streams lead to the sea. Some end in lakes or other streams. These streams carry material into the lakes. In time the lake fills up with mud, dirt, sand and the like. W hen this happens, the lake turns into a shallow marsh. In time the marsh may dry up. This is an­ other place from which the wind and water may take away the land.

W hen the land is being moved by the wind or water, we say it is eroding. The process of erosion is going on all of the time. It may be helpful, but more often it is harmful in destroying much valu­ able land.

ON S EACOAS TS , OCEAN WAV ES ERODE THE LAND. THE WAVES CARRY LOOSE B I TS OF ROCK. THESE BITS OF ROCK, PLUS THE FORCE OF THE WAVES AGAINST THE LAND, WEAR AWAY THE EARTH.

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S ED I M E N T A RY ROCKS

BODIES OF WATER HOLD MUD, SAND AND ROCKS, AS WELL AS LIVING THINGS, IN­ CLUDING PLANTS AND SEA ANIMALS . MANY OBJECTS SINK IN THE WATER- SOME TO THE VERY BOTTOM, OTHERS ONLY PART­ WAY. IN TIME, THERE ARE LAYERS OF ROCK, SAND AND MUD IN THE WATER.

Are there rocks

under the water?

STIR

h a n d f u l o f u p a dirt in a glass of water. At first the water will be cloudy. But if the water is left alone, the dirt will settle to the bottom of the glass. In

time the water will be clear again. The dirt that has settled to the bot­ tom of the glass is called sediment. From this word comes the name sedi­

mentary, the name for the second big group of rocks.

This kind of rock was formed by sediment from rivers and streams. E very day the streams and rivers bring

more and more mud, sand and rock to the seas. These settle to the bottom and are called sediment.

The big rocks settle first. They sink first because they are bigger and heavier. N ex t the sand and then the mud sinks

to the bottom of the sea. In this way diff erent layers are built up. The lay­ ers build up on the sea bottom year after year until they are very thick.

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VOLCANIC TUFF IS SEDIMENTARY ROCK. TUFF IS COM­ POSED OF MANY LAYERS OF VOLCANIC ASHES AND DUST. THESE LAYERS BUILT UP AROUND ACTIVE VOLCANOES.

The weight o f the layers o f san d an d. water abo ve press do wn on th e bo ttom layer o f san d. This bo ttom layer b egin s to change.

E ach tiny grain o f san d b egin s to stick to ano ther o ne. The san d grain s chan ge in to ston e. Because the ston e is made fro m san d, we call i t san dston e. Sandston e is a sedim en tary ro ck.

M ost sedimen tary ro ck is m ade un ­ der the water in lakes o r seas an d in th e oceans. But so meti mes sedim en tary ro ck is made on dry lan d!

Fo r instance, lon g ago , man y vo l­ cano es ble w o ut ashes an d vo lcan ic dust . which settled aro un d them . Y ear after year the laye rs b uilt up. In time ano ther kin d of ro ck was m ade- sedim en tary ro ck called vo lcanic tuff .

In the We st, large areas are co vered with th is kin d o f ro ck. Th e diff er en t layers are o f di ffer en t color s, m akin g a co lo rful sedim en tary ro ck.

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How are rocks made?

T

N

OT. ALL sed­Im e n t a r y rocks were made

from dirt and sand that came down the river. Some were made from the shells of sea animals and plants.

Millions of animals live in the sea.

Some of them build a hard shell which is made of lime, and this protects the animal living inside. Clams and snails live in shells.

Some plants have shells, too. A dia­ tom is a tiny plant that lives in a shell. Millions and millions of tiny shelled diatoms live in the sea.

When a plant or animal dies, its shell

MOON SHELL SCALLOP

CLAM

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sinks to the bottom of the sea. After many years, millions of dead shells pile up on the bottom of the sea. Again, the top layer pushes down on the bottom layers. The shells in the bottom layer are pushed close together.

The weight of the shells on top changes the bottom layer of shells. The shell layer at the bottom turns into stone. The name of this stone is lime­ stone, which is another kind of sedi­ mentary rock.

Look again at the word limestone. Do you see that the first part of the word says lime? This tells us what the rock is made of. The last part of the word tells us the lime has turned into stone.

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Where are sedimentary

rocks found? were fo rmed under

S

E DIM E N ­TARY ro cks

th e s e a s an d oceans. Th e sedi mentary ro cks built up higher and high er in so me places. This made the sea bo tto m rise h igher and higher.

M illions of y ears went by . In so me places the sea bo tto m ro se slowly . If it ro se high eno ugh, i t came o ut o f the water.

Th e land that came o ut o f the water was made o f sediment. Below th e to p lay ers of sediment were sedimentary rocks. Y ou can see th ese rocks to day near th e seashore.

SEDIMENTARY ROCK THAT CAME OUT OF THE WATER OFTEN ROSE TO GREAT HEIGHT.

YOU CAN SEE HOW LAYERS OF SEDIMENT WERE BUILT UP AS YOU DRIVE ALONG HIGH­ WAYS WHICH CUT THROUGH HILLS MADE

OF SEDIMENTARY ROCK.

NEAR THE SEASHORE, YOU CAN SEE SEDI­ MENTARY ROCK . LAYERS OF SEDIMENT DE­ POS ITS I N THE WATER ROSE HIGHER AND HIGHER. AFTER MANY YEARS, SEDIMENTARY ROCK EMERGED FROM THE WATER.

W herever yo u find land that was o nce under water, yo u are almo st sure

to find sedimentary ro ck.

Ro ads are o ften cut thro ugh hi lls. If the h ill is made o f sedimentary ro ck, it will show the lay ers. Yo u can usually find sedimentary ro cks in hills that are

lay ered.

Sedimentary ro cks are very co mmo n and may b e fo un d almo st every where. Th e midwestern part of our co untry is

covered with sedi mentary ro cks. Large areas o f the East are made o f th is ty pe of rock. The W est also has its sh are o f sedimen tary depo si ted ro ck.

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Are there

many kinds of

sedimentary rocks? sedimentary rock.

CONGLOM­

ERATE is a

It is made of a mix­ ture of smooth round stones and pebbles. The larger stones in a con­ glomerate rock are held together by another kind of stone, either limestone or sandstone.

Conglomerate rock is made in old streams and river beds. The large stones are washed down the stream. Then, in a quiet pool, the rocks sink to the bot­ tom and pile up.

More rocks and sand continue to pile up in the old stream bed. In time the big and little rocks become changed into conglomerate rock.

SANDSTONE

22

CONGLOMERATE

SANDSTONE is a very useful sedi­ mentary rock. It is used in walls and buildings, because it is strong and easy to quarry. After it has been taken from the quarry, it is cut into blocks and used in the building of things.

There are many different colors of sandstone. Brown is common. In some places so much sandstone is colored brown it is called brownstone. You can also find yellow-colored, gray-colored and red-colored sandstones.

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SH ALE is made from fine silt and mud. Another name for it is mudstone. Yet, sometimes it is so soft, it is not like

a stone at all.

M ost rocks do not have any odor, b ut wet shale does. It smells li ke damp

ear th .

Y ou can fi nd shale s of many diff er­ ent colors. Red, b rown and g ray are common co lor s of sh ale . T he color, o f cour se, de pe nd s upon the color o f the mud or fi ne sil t from wh ich the sh ale was made .

LIMESTONE

LIMES TONE is a se dime ntary ro ck that forms only under w ate r. It take s millio ns of year s to m ake a l ot o f l ime ­ stone . So me de posits of lime stone are thousands of fe et thick!

Pure limestone i s cle an and w hi te . But often other thing s ge t mixe d into the limestone that may ch ang e its co lor . W hen a li ttle b it of iron g ets mix ed

into it, the white limestone ch ang es to yellow or b rown. Other mater ial s can chang e the color of lime stone to g reen, gray, black and many other colors.

DOLOMITE

DOLOMITE is another kind o f lime­ sto ne made under th e se a. I t is usually white or lig ht-colored . One kind o f dolomite b re aks up e asily . Thi s kind looks just like whi te rice !

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M ET A MORPH I C R O CKS

LIMESTONE

MARBLE

Why do rocks

have different

T

HE NAME metamorphic shapes and colors? means "to have

been changed." This name is used to tell about rocks that have been changed in some way. This is the third and last big group of rocks.

Metamorphic rocks began as one kind. of rock and later were changed into another kind. All of them began once as igneous or sedimentary rocks. The new rocks do not look the same, for in becoming metamorphic rocks their structure and often their color change.

24

Sedimentary rocks are formed deep under the seas. After they have been formed, they may become very hot. Heat helps to change sedimentary rocks.

The weight of the rocks and water on top of the sedimentary rocks is very great. The heavy weight or pressure also helps to change the sedimentary rocks . Heat and pressure together change the sedimentary rocks into meta­ morphic rocks.

When limestone is changed, it turns into marble. If shale is changed, it turns into slate. Both marble and slate are metamorphic rocks.

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THE HEAT AND HEAVY WEIGHT, OR PRESSURE, ON SEDIMENTARY AND IGNEOUS ROCKS HELP TO CHANGE THEM INTO METAMOR­ PHIC ROCKS. AS A VOLCANO PUSHES ITS WAY UP THROUGH THE EARTH, GREAT HEAT IS CREATED. AS THE VOLCANO PASSES THROUGH A SEDIMENTARY LAYER, THE HEAT CHANGES THE SEDIMENTARY ROCK INTO METAMORPHIC ROCK.

Where do metamorphic

rocks come from?

SEDIMEN­

are made deep un-TARY roc ks der the seas and oc ean bo ttoms. So metimes a sea goes dry. The land moves up and the sedi­ mentary rocks are exposed.

In time the wind and rain wear down the to p layers o f roc k. Then ano ther kind of rock is expo sed. The ro ck ex­ posed is metamo rphic ro ck.

To find metamo rphic ro ck, yo u must visit a place where the land has been wearing down fo r many years. There are piaces in the eastern U nited States and a few in the West where o ne c an see this kind o f roc k. There are also many metamorphic roc ks far no rth in Canada.

So metimes metamo rphic roc ks can be found where old vo lc anoes o nc e

sto e>d. The red ho t lava fro m them o ften changed o ther roc ks into metamo rphic rocks.

This typ e o f metamo rphic roc k co uld occ ur where the vo lc ano pushed its way up thro ugh the earth, passin g thro ugh a sediment layer o n the way. Here the heat helped to c hange the sedimen tary roc k into metamo rphic roc k.

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26

Are there

many kinds of

metamorphic rocks?

S

ph ic rock made L ATE is a m e t a m o r ­

from th e sedimen­ tary rock sh ale. Wh en sh ale is chan ged b y heat and pressure, it turns into slate.

S late an d shale have the same colors, b ut th ey do not look alike. They look

diff erent b ecause of h ow th ey b reak. Th e way th at th ey break h elps to tell th em apart.

S late b reaks into smooth fl at sh eets of rock. Y ou can split it into very th in pieces, which make fine steppingstones.

Th e finest b lackb oards are made of slate th at has b een split into th in sheets. One side is then polish ed very smooth b efore it is used for a b lackboard.

Sh ale will not b reak into smooth fl at sh eets of rock. It b reaks only into odd sh apes. This stone h as little use b ecause of the way in wh ich it breaks.

CHLORITE SCH IST

SLATE

SCHIS T is a metamorph ic r ock made from mudstone or shal e. Rock must b e ch anged many times in order to make sch ist.

As schist is made, some of the min­ erals in it chan ge. These minerals th en b ecome mica an d all are turned th e same way. The little b its of mica make th e schist sh ine and sparkle.

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SERPENTINE

SE RPE NTINE is a metamorphic roc k often c olored green. Some serpen­ tine roc ks are light green and some are dark green. This stone is slippery to touc h. It feels as if it were c overed with wax or soap.

When this rock is exposed to the weather, it soon breaks down and

crumbles away.

QU ARTZITE is a very hard meta­ mo rphic roc k made fro m hard sand­ stone.

Pressure and heat c hanged the sand­ stone into hard q uartz ite. Some quartz ­ ite is c olored l ike sandstone. These colors are yellow, brown, pink and red.

BLACK MARBLE

WHITE MARBLE

M ARBLE is a metamorphic rock.

It c omes from limestone that has been c hanged by heat and pressure. M arble

is made- over limestone.

M arble is often many different colors. You can find white marble or black

marble or just about any color in be­ tween. Often the marble is striped or marked with several colors. M inerals, or impurities, in the marble change its c olor.

This stone is used in some of the great public buildings in our country. M any b eautiful monuments are made

with this useful stone.

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EPIDOTE AMAZONITE (or Amazon stone)

Triclinic System

Monoclinic System

C RY S T A LS

What is

a crystal?

THERE

n o n- l iv i n g a r e sub stances which grow into bodies of various shapes. They grow by adding on more layers

of the same substance, keeping the same shape at all times. These bodies of various shapes are called crystals. M ost solid substances, like minerals, are crys­ talline; that *s, they are made up of crystals. So a crystal is really another fo rm o f ro cks and minerals, ex cept that the word " crystal" tel ls us that the rock or mineral is of a certain shape.

These different crystal shapes, which help us to tell the minerals apart, are gro uped into six main kinds or systems: Cubic System, Tetragonal System, Hex ­

agonal System, Orthorhombic System, Mo no clinic System and Triclinic Sys­

tem. Ex amples of the six differe nt shapes may be seen in the crystal forms shown on this page.

When minerals are first formed, they ·often turn into crystals. It takes a long time to make big crystals, but some little crystals can be made in two day s.

28 SULPHUR Orthorhombic System CALCITE Hexagonal System RUTILE Tetragonal System HALITE (salt) Cubic System

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How can you

make a crystal?

H

ERE is a way to make so me

crystals o f your o wn. Salt cry stal s are easy to make.

Stir three tabl espoo ns full o f salt into a cup o f warm water. As yo u stir the water, the salt wil l disappear. In a few minutes yo u will no t b e able to see the salt crystals. T hey have disappeared into the water.

Next po ur the salty water into a pie pan. Set the pan where it will b e warm. Salt crystals wil l gro w faster in a warm

place.

Now yo u must wait fo r the water to evapo rate. Thi s may take a few day s. L ittle by little the water will disappear. E very day loo k at the pan o f salt water. Soo n white c rystal s will b egin to fo rm aro und the edge o f the pan. The white crystals are made o f salt. Sugar crystals can b e made in the same way . Even b igger c ry stals than sugar o r salt c an b e made by disso lving al um crystal s. When they turn b ac k into cry stal s again, yo u will b e surprised at their siz e. Yo u can b uy al um at any drugsto re fo r a few cents.

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' "

M I N E R AL

Where does the

salt we eat

come from?

FOODS

MUCH

o u r s a l t i s OF

made near the

sea-shore, in large flat ponds filled with sea water. This water contains lots of salt.

Day after day the hot sun shines and warms the sea water in the pond. Warm sea water helps ·the salt crystals to form.

As each day goes by, a little more water disappears by evaporation. Salt crystals form in the water that is left. After many days, the sea water is all gone and only the salt is left behind. The salt has formed as white crystals on the bottom of the dry pond.

When the pond is dry, workmen can gather the salt. The salt is put into little boxes for us to use. Everyone uses salt crystals left behind by the sea water.

Many years ago salt was difficult to get in some countries. Workmen have even been paid wages with salt, instead of money!

This kind of salt has another name

- halite. Halite is the mineral name for salt, but most of the time halite is just called salt.

SALT PONDS USED I N THE EVAPORATION OF SEA WATER

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Can we eat

minerals?

You

surprised to M AY be

learn that every day yo u eat many

diff erent minerals besides salt. These

minerals are very helpful to yo u.

Water is a very co mmo n mineral. It is the mo st impo rtant mineral you use. Some of it is in the foo d yo u eat. Other water is in the milk yo u drink. Your body needs some water every day.

You only need to eat very tiny amounts o f the o ther minerals which are found in foods. They cannot be seen because there are o nly tiny bits of them. B ut they are very important.

Iron is an impo rtant mineral used to make cars and other things. It is also a mineral yo u need to eat. It is fo und in eggs and liver. Calcium is a mineral fo und in cheese, and it helps to make stro ng bones. Iodine is a mineral needed to keep your bo dy healthy. Io dine is often mixed with the salt yo u eat.

All of these minerals and many more are fo und in the foo d yo u eat. Yo u need to eat many diff erent kinds o f fo od be­ cause each kind has diff erent minerals. They help you to build a healthy body.

0

.

EGGS AND MEAT (iron)

CHEESE (calcium)

S ALT (iodine)

FISH (phosphorus)

BEANS AND PEAS (copper and manganese)

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32

RO CK-FORM I NG M I N E R A L S

What are some of the rock-forming

minerals?

R

one or more kinds OCKS a r e made from of minerals. Gran­ ite is a rock made from three kinds of minerals - quartz, feldspar and mica.

Quartz, feldspar and mica are rock­ forming minerals. They are called that because they make rocks, like granite.

QUARTZ is one of the most com­ mon rock-forming minerals and is found in all the big groups of rocks - igneous, sedimentary and metamorphic rocks.

Some quartz is colorless, like ice.

ROCK CRYSTAL IN DRUSY QUARTZ

SMOKY QUARTZ

Other colors are white, pink, violet and gray. Sometimes the dark-colored quartz is called smoky quartz. It looks

like the color of dark smoke.

You can find quartz very easily. The small sand grains in dirt are often quartz. Beach sand is usually full of quartz grains. It is found in most igne­

ous rocks, often in the form of crystals. In fact, the names of many minerals and rocks depend upon whether or not quartz is present in the sample. You should consider quartz to be one of the most important rock-forming minerals.

CITRINE QUARTZ

AMETHYST QUARTZ

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FELDSPAR is a very commo� rock­ forming mineral, like quartz. But the name feldspar is really a family name. That is, it is a name used for six or seven different feldspar minerals.

All of these feldspar minerals are much alike, sometimes so much so that it is hard to tell them apart. It is easier to just call them feldspar. So feldspar is the family name given to all of them.

Feldspar minerals occur in almost all of the igneous rocks. Often the color of the rock depends upon the color of the feldspar mixed into it.

GRANITE WITH PINK FELDSPAR

GRANITE WITH WHITE FELDSPAR

MICROCLINE FELDSPAR

Feldspar may be colored white, light pink or even green. The white and pink colors are the ones you will see most often.

Granite with pink feldspar will look pink. If the feldspar is white, the gran­

ite will look white. The quartz in the granite helps to change the color, too.

As granite grows old and is exposed to the weather, it begins to fall apart. We say that it is beginning to decom­

pose. Actually, it is the feldspar in the granite that is breaking apart. In time the wind and water help to change the feldspar into clay .

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IDENTIFICATION OF ROCKS

AND MINERALS

How do we begin to identify rocks

and minerals?

THERE

to identify rocks several ways ARE

and minerals. First you will have to make some tests. These tests are easy to do and will help you to know more about rocks and minerals.

Each test you make will tell you more about your new rock, until at last you will be able to tell the rock's name.

You must not expect to be able to name every new rock or mineral at first. In the beginning you will be able to name only a few. It takes a long time to learn most of the names of the rocks and minerals.

One of the first tests you will make is to ask yourself, "Where did this rock come from?" Is it an igneous rock? Or does it look more like a sedimentary rock? It might be even a metamorphic rock!

You would first like to know what general kind of rock it is. When you know where it came from, you can often tell what general kind it is.

Once you know if it is an igneous, sedimentary or metamorphic rock, you

can make some other tests.

34

GRAN ITE I S AN IGNEOUS ROCK COLORED RED, PINK, YELLOW OR BROWN . IT IS USED OFTEN IN CONSTRUCTION WORK.

CONGLOMERATE IS A SEDIMENTARY ROCK MADE OF STONES AND PEBBLES, HELD TO­ GETHER BY LIMESTONe OR SANDSTONE . LIMESTONE IS OFTEN WHITE AND SAND­ STONE IS USUALLY BROWN .

MARBLE IS A METAMORPHIC ROCK USUALLY STRI PED OR MARKED WITH SEVERAL COL­ ORS. IT COMES FROM LIMESTONE . MARBLE IS WI DELY USED IN MONUMENTS.

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IN THE F I ELD, THERE ARE SOME SIMPLE ·WAYS TO TEST THE HARDNESS OF ROCKS

AND MINERALS.

YOUR FINGERNAIL CAN SCRATCH TWO MINERALS- TALC AND GYPSUM.

A PENNY IS HARDER THAN YOUR FINGER­ NAIL AND CAN SCRATCH CALCITE, AS WELL

AS TALC AND GYPSUM.

THE BLADE OF ·A SMALL POCKET KNIFE IS HARDER THAN A PENNY. IT CAN SCRATCH FLUORITE AND APATITE, AS WELL AS THE MINERALS BELOW THEM ON THE SCALE.

HARDER MINERALS CAN SCRATCH THE SOFTER ONES, AND EACH MINERAL CAN SCRATCH ANOTHER OF ITS KIND.

O

NE o f t h e most impor­

rock or mineral is? tant tests you can How can you tell

how hard a

make on a speci­ men is to find out how hard it is. Hard­ ness tells you how easy it is to scratch one mineral with another. Some miner­ als are very soft. Others are very hard.

If you know how hard or soft a specimen is, it will help you to tell it apart from other minerals.

Geologists, for a long time, have used ten minerals to test for hardness. These ten minerals are called the Scale of Hardness minerals.

Each mineral on the scale has a num­ ber as well as a name. You have already read about the names of some, and others will be new to you.

There are also some common things that will help you to test for hardness . . One of these testers you have with you all of the time your fingernail -which will scratch at least two minerals. A penny can also be used to scratch certain minerals, and a small pocket knife is another common tester. Its blade will scratch still other minerals. Each mineral can also scratch itself. You will read about these and others in the dis­ cussion about the ·"Scale of Hardness" minerals, beginning on the next page.

These minerals have been arranged in order. The softest mineral is number one and the hardest is number ten. Those minerals in between will vary, each higher-numbered mineral being harder than the one before.

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S C A LE O F

T H E

H A RD NES S

M I N E R A LS

What are the

hardness minerals?

N

U MBER TALC: Talc 1. is a metamorphic mineral. It is the softest of the minerals in the scale. You can scratch talc with your fingernail.

Talcum powder is made from ground­ up talc. Of course, the nice smell is put in after the talc is ground up.

GYPSUM

Number 2. GYPSUM: Gypsum is a

sedimentary mineral. It is harder than

talc, but y ou can still scratch it with your fingernail.

Gypsum may be colorless or white. It is found in huge beds in the ground where it is dug out. Gypsum is an im­

portant mineral. Plaster of Paris is made from it. Plaster wallboard is also made from gypsum. Did you know that the blackboard chalk you use in school was made from gypsum?

36

FOLIATED TALC ON SERPENTINE

CALCITE

Number 3. CALCITE: Calcite is third in the hardness scale. It scratches talc and gypsum. You can scratch calcite with a penny.

Calcite is a colorless or white min­ eral. You will find it in many places and with all groups of rocks.

A special form of calcite is Iceland Spar. When you look through a clear crystal of Iceland Spar, everything sud­ denly looks double!

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FLUORITE

Number 4 . FL UORITE: This mineral is one of the most colorful of the hard­ ness minerals. Crystals of fl uorite may be whit e, gray, black and many other

colors. They may also be colorless.

Fluorite is four on the hardness scale, but you can scratch it with a sma11 pocket k nife.

Number 5. APATITE: Apatite is an­

other mineral that forms beautiful crys­ tals of many diff erent colors. Some of these colors are white, br own, green, violet, blue and yellow. Yellow is the

most common color.

y ou c an scratch apatite with a k nife, too. Ap atite in turn will scratch any of the hardness minerals below it. Apatite, like each of the other minerals, is able to scratch itself.

Number 6. FELDSPAR: Feldspar is

about the mos t common mineral on the earth. W hen this mineral breaks up and r ots, it turns into clay. Clay is found

almost everyw here.

Your knife will not scratch feldsp ar, bu t the feldspar will scratch your knife!

QUARTZ

Number 7. Q UA R TZ: Qu ar tz is a

comm on mineral you have already read ab ou t. I t comes in many colors. A beau­ tifu l ki nd of qu artz is named Tiger's Ey e and is used in j ewelry.

Q uartz sand i s mel ted and turn ed i nto clear glass. R adios and phono­

grap hs-. very often have sp ecial qu ar tz cr ystals in them. Quartz is very usefu l. I t is the hardest mineral you are ap t to fin d easi ly .

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Number 8. TOPAZ: Topaz is a very

hard stone. It will scratch quartz or any of the other minerals below quartz. Topaz is prized as a gem stone because it is very beautiful. This stone is com­ monly yellow.

Number 9. COR UND UM: Corundum is next to the hardest mineral. Some crystals of this mineral are also gem stones. Ruby is a clear red corundum crystal. Such a crystal is quite valuable.

Ordinary corundum is crushed into small bits and made into sandpaper.

38

Number 10 . DIAMOND: This is the

hardest mineral known on earth. N oth­ ing is harder than diamond. It is many times as hard as corundum. Clear crys­ tals are. made into jewels. Dark-colored diamonds are used to polish and cut other hard stones, as well as other diamonds, too. Diamonds are valuable because they are very hard, beautiful and rare.

· These are the hardness minerals.

They are all used for many things. Test­ ing the hardness 'of other minerals . is just one of the things for which they are used.

, As you become more interested in rocks and minerals, you will want to have a set of hardness testing minerals. A set is not expensive, for most sets do not contain a diamond. Since a dia­ mond could only test another diamond, there is little need for one in the set.

Even before you have such a set, many tests can be made with your finger­ nail, a penny, a pocket knife and a piece of quartz.

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How can you tell what kind

S I M P L E

Y

OU CAN test for the name

of rock it is?

of a rock or min­ eral with a streak plate. A streak plate is made of unglazed tile.

M any specimens leave a col ored streak when they are rubbed on the streak plate. The color of the streak helps to name the rock. Y ou can make red, b lue, bla ck and many other col ored streaks. Some samples will not even

make a streak!

T E S T S

RUB THE ROCK OR THE MIN ­ ERAL ON A STREAK PLATE.

THE STREAKS MADE BY THE HARDNESS MINERALS VARY FROM WHITE TO GRAY, WH ILE SOME OF THE MINERALS MAKE NO STREAKS OR ARE COLORLESS . GENERALLY, NON-METALLIC M I NERALS MAKE COLORLESS TO LIGHT GRAY STREAKS, AND METALLIC M I NERALS MAKE DARK GRAY TO BLACK STREAKS .

A SIMPLE WAY TO TEST ROCKS AND MI N­ ERALS FOR WEIGHT IS TO HOLD A DIFFERENT SPECIMEN IN EACH HAND. EVEN THOUGH BOTH ROCKS ARE OF THE SAME SIZE, ONE WILL WEIGH MORE THAN THE OTHER.

How can you test a rock

or mineral for weight?

Y

NOT look at a O U C A N ­ rock or miner al and tell how h eavy it is. Yet, some minerals or rocks are much heavier than others. When y ou pick up a sample rock, you can tell if it seems heavy or light.

When you try this with a diff erent rock in e ach hand, you can tell which is the heavier. B oth samples must be about the same size, of course. Y ou will be surprised to see how easily y ou can tell the diff erence in weight between two r ocks. Whether the rock is heavy or

li ght may help to tell its name.

M ore advanced book s will show y ou other ways of finding the weight of a rock or minera l.

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What is a fossil?

F O S S I L S

AFOSSIL

remains of is the some anim al o r plant which is no longer living. It has b een dead for many years and only p art of the animal or plant is left today. This part is called a fossil.

Clams often tum into fossils. H ere i s how this can happen.

When a clam dies, the soft parts of its b ody soon rot away . But the shell of the clam is very hard. It is made of calcium, like our b ones, and cannot rot away. The shell sinks to the sand at the b ottom of the sea.

M any years pass and other shells join the first shell. Fine sand washes over the shells an d b uries t hem. In time the sand changes into sandstone. B ut the shells are still there, bur ied with the sandstone.

M illions of years go by and the se a b ottom b ecomes dry land. The sand­

stone can now be seen.

If you should dig down into the sand­ stone, y ou would find the old clam shells. You would call them fossils now. They are called that b ecause fossils are hardened traces of animals or p lants which have b een preserved in the earth.

HERE ARE CLAM SHELL FOSSILS WH ICH HAVE BEEN PRESERVED I N SANDSTONE .

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THE WORD FOSSIL COMES FROM A LATIN WORD MEANING "DUG UP. " THE DISCOVERY OF FOSSIL REMAINS OF ANIMALS ON LAND AND IN THE SEA HAS GIVEN SCIENTISTS MUCH INFORMATION ABOUT THE WOR LD AS IT WAS MILLIONS OF YEARS AGO .

Why do we

study fossils?

S OME

y ou may fi nd d a y a fossil. Y ou will want to know its name. Y ou ma y ask y ourself, "W here did this come from? Is it an animal or is it a rock? H ow did

it get here? Is it valuab le?" The se and man y other questions may occur to you.

T he sc ien tists w ho search f or fossils an d study them are kn ow n as paleon­ tologists. By learn ing of life and changes

that oc cu rred on earth in the past, tb_ ey c an su pply an sw ers f or the future.

F ossils give us a record and a pictur e of the past that is b ey ond the ken of human memory. F rom them w e can fin d o ut not only w hat certain plants and . an imals looked like, b ut can deduce other things. F or example, b y fi nding f ossil shel lfi sh in presentl y mountainous region s, w e can scientific ally con clude that th e area was on ce un der sea w ater. By fin din g f ossils of tropical plants in G reen land, w e must con clude that this lan d mass on ce had a climate quite dif ­ feren t f rom w hat it has today.

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Where are

fossils found?

ONE

places to look of the bes t f or fossils is in se di­ mentary rocks. Soft sh ale and sandstone of ten have fossils in them. These are both sedimentary rocks.

L imestone is a sedimentary rock made up of millions of tiny shells of sea animals. Sometimes the shells of the animals can b e seen in the limestone. Y ou could think of this kind of

lime-stone as " fossil lime-stone ."

GOOD EXAMPLES OF PETRIFIED WOOD MAY BE FOUN D IN THE PETRIFIED FOREST NA­ TIONAL PARK IN THE STATE OF ARIZONA.

THE SHELLS OF SEA ANIMALS CONTRIBUTE TO THE FORMATION OF LIMESTONE. LIME­ STONE IS, THEREFORE, A GOOD SOURCE OF FOSSILS . NOTE THE SHELLS IN THIS STONE.

Trees and plants that are near lak es and streams often fall into the water. Sometimes they sink to the bottom and are buried in the soft mud. The y ears pass b y. M ore mud covers the ol d trees. Slowly the trees change into fossils.

This takes many years to occur. But finally the t ree has been changed from wood into a mineral. It is no longer made of wood, but of stone. We call this kind of stone petrifi ed wood.

There are places in the West where whole forests of petrifi ed trees or fossils are found. Some areas have been set aside as national or state monuments to preserve these trees and f ossils from souvenir hunters. You may some day visit one of these places yourself.

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R A RE

What makes a mineral

a gem stone?

S TON ES

GEM

rare and more stones are

difficult to find

t h a n ord i n a r y rocks. Th ey ar e harder to find because there are not so many of them. If a stone is hard to find, if it is beautiful, and if it can be polished, it th en be­ comes valuable. This kind of stone is named a gem stone.

For h undreds of year s m en h ave looked for valuable gem stones and minerals. T oday other men are still h unting for new places to find gem

stones.

A rub y is a beautiful red- colored gem stone. W hen a ruby is polish ed, it sparkles and shines. The color of the ruby h elps to make it valuable.

Other gem stones are opals, pearls, emera lds and diamonds. E meralds and diamonds are the most ex pensiv e and rarest gem stones. All gem stones are beautiful. Gem stones are used m

j ewelry. Th ey are often set in rings.

STAR SAPPHIRE EMERALD SAPPHIRE OPAL D I AMON D RUBY 4 3

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What is

pumice?

P U M I C E

P

UMICE is an igneous rock.

It is made by vol­ can oes. Sometimes

the volcan o thr ows out gobs of molten r ock. L ittle holes gr ow in the rock b e­

for e it cools . T hese holes are cause d b y steam or gas tr apped in the molten rock. T he holes in pumice look just like the holes in a loaf of br ead!

Pumice is a ston e that can fl oat on water ! It fl oats on water because it is so very light.

T his s ton e is used to polish fine fur­ niture an d to mak e b uilding materials.

COAL 44 What is coal? PUMICE

COA L

COAL

sedimen tary I S A rock that will burn.

Coal bum s just as wood does. It is used to build war m fires.

Coal was made million s of years ago. This rock is made fr om plants, and tr ees or fern s that lived lon g ago.

Th ese tr ees an d p lan ts b eca me b ur ied just like fos sils. In time they turn ed into coal. Coal is really the remain s of many tr ees an d plan ts. Y ou can think of coal as " fossil wood."

Coal deposits ar e foun d all ove r the Un ited S tates. T he largest an d b est ones ar e in the eas tern par t of our countr y.

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ICE . . .• . .

A S B E S TOS

What is

asbestos?

ASBESTOS

a mineral that is

does not burn! It is useful around stoves and hot places, for it wi ll keep things near the stove from burn ing.

Asbestos is a light- colo red mineral that comes fro m a kind of serpentin e. I t is made in to asbestos cloth, asbesto s paper an d o ther helpful thin gs. If you wore a pair o f asbestos gloves, yo u could touch and handle ho t thin gs with­ out getting burned!

What is

ice?

I C E

I

CE IS THE col­orless mineral t h a t f l o a t s i n water! Ice is really a w ater c rys tal, fo rmed w hen the tem-peratur e of w ater o r mo isture in the air reaches the freezing point, in dicated by

32° o n the F ahrenh eit thermometer or on the c en tigrade thermometer.

Ic e expands ( in creases its vo lume) as it fo rms . If on e w ere to measure out el even eq ual parts of w ater an d f reez e it, on e wo ul d fin d that it takes up as m uc h s pac e as tw elve parts . W hen there is no room fo r w ater to expan d, pr es­ sur e b ecom es s tron g - w ater pipes , f or

exam ple, w ill of ten s pl it open in w inter. Ic ebergs , bein g lighter than w ater, wi ll floa t. In the s ea abo ut on e-eighth of an ic eb erg is vis ibl e - the r es t o f it is

hidd en be low the s urf ac e.

AS BESTOS

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46

S T A R T A R O C K A N D M I N E R A L

C O L L E C T I O N

How do you begin

you

will find it

a rock and easy to star t a

mineral collection? rock and miner al collection. Begin to collect by looking near your home.

If you have a garden, you may find a roc k ther e. If there is an open fi el d cl ose by, it should contain some r ocks you wil l want to have in your collection.

Are wor kmen building a new house nea r your home? They may have dug up some rocks or miner als you do not have. Sometimes the buil der s br ing in new kinds of rocks. L ook them over.

Ther e might be some you wil l w ant to collect, but ask permissi0 n fir st.

If you go into the country , watch for other new r ocks or miner als. L ook at new r oad cuts. This is often a good place to collect r ocks. A dry cr eek or stream is a nother exc ell ent plac e to l ook.

One of the finest pla ces will be in a r ock quarr y. H er e you ar e sure to find some worthwhil e spec imens. Of course, you must be careful to watch out for overhanging r oc ks or l oose stones. It is well to col lec t with a partner - and

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What will you

need to col lect

Y OU

need some-W I L L

rocks and minerals? thing to put your

specimens in when you find them. If you are collecting near home, a heavy paper bag will do. But put in only a few small rocks at a time. Most collectors use a collecting bag made of strong cloth. It has a strap that goes over your shoulder to help carry heavy loads. Surplus goods stores usu­ ally have a bag of this kind.

You will often need to break off rocks and break open new ones. A ham­ mer or even another stone will some­ times help. With a hammer, or a pros­ pector's pick, you can chip off a small piece of rock from a larger one.

Rock and mineral collectors like to take home only one or two of each kind of rock they find. It does not help to take too many of each. You would soon run out of room in which to keep them.

How can you keep your rocks

and minerals?

Y OU

your best rocks want to keep W I L L and minerals. It will help if you keep each kind together. The igneous rocks can go into one box. All of the sedimentary and the meta­ morphic rocks should be put into other boxes.

Shoe boxes or wooden cigar boxes make good containers. A label on the outside of the box will help you to lo­ . cate specimens quickly.

Each rock should be labeled sepa­ rately before you put it into your col­ lection bag. A good system is to put a

piece of adhesive tape with a number on it on the sample. In your collecting notebook write the name of the speci­ men and where you found it. Later on, at home, paint a small round white spot on your specimen with w};lite paint. India ink numbers over the white paint will show up fine.

Start your numbers with one, two, three, and so on. This will help you to keep your collection organized. Do not carelessly try to collect everything and put off labeling your rocks until later.

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IDE N T I F I CAT ION C H A RT OF M AJOR S P E C I M E N S

IGNEOUS ROCKS

S LATE

I SCH I ST

THE SCALE OF HARDNESS MINERALS

2. GYPSUM

7. QUARTZ

GEM STONES

SAPPH I RE EMERALD

CRYSTALS

AMAZO N ITE EPI DOTE

SERPENT I N E Q U A RTZITE

3. CALC ITE 4. FLUORITE

8. TOPAZ 9. CORUNDUM OPAL RUBY . S U L P H U R RUT I L E '. ' -::. -MARBLE 5 . APAT I T E 1 0. D I AMOND PEARL HALITE

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·. i

'

·-P rodu ced a n d app roved by n oted aut h o rities, t hese books answe r the q u est i o n s m ost often asked about ' sc i e n c e , n at u re and h i story. They are p resented in a c l ear, readab l e style, and contai n many c o l o rf u l a n d i nst ructive i l l ustrat i ons. Read e rs w i l l want to exp l o re eac h of t h ese fasc i n at i n g su bj ects and c o l l ect t h ese vo l u mes as an authent i c , ready-refe re n c e , b as i c l i b rary.

500 1 D I N O S A U R S 5032 D O G S 5002 WEAT H E R 5033 P R E H I STO R I C M A M M A LS 5004 R O C K S & M I N E RALS 5034 S C I E N C E E X P E R I M E N T S 5007 I N S ECTS 5042 THE A M E R I CA N R E V O L UT I O N 5008 R E PT I L E S 5046 M A G N ETS A N D M A G N ET I S M 5009 B I R D S 5053 T R E E S 501 1 B E G I N N I N G S C I E N C E 5055 N O RT H A M E R I CA N I N D I A N S 501 3 T H E H U M A N B O D Y 5064 STA RS

501 4 SEA S H E L LS 5065 A I R P LA N E S A N D THE STO RY

501 6 T H E M I C RO S C O P E O F F L I G HT 5021 C H E M I ST R Y 5066 F I S H 5022 H O R S E S 5069 T RA I N S A N D S H I PS 5024 P R I M I T I V E M A N 5070 E C O L O G Y 5031 W I LD FLOWE R S A N D O T H E R T I T L E S

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References

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