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Glossary

Rocks and Minerals

Scott Foresman Science 4.6

StandardsPreview

Standard Set 4. Earth Sciences

4. The properties of rocks and minerals reflect the processes that formed them. As a basis for understanding this concept:

4.a. Students know how to differentiate among igneous, sedimentary, and metamorphic rocks by referring to their properties and methods of formation (the rock cycle).

4.b. Students know how to identify common rock-forming minerals (including quartz, feldspar, mica, and hornblende) and ore minerals by using a table of diagnostic properties.

ISBN 0-328-23556-3

Vocabulary

cleavageigneouslustermetamorphicmineralorerock cyclesedimentarystreak

Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Unless otherwise acknowledged, all photographs are the property of Scott Foresman, a division of Pearson Education.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd)

Opener Kevin Schafer/Getty Images

2 DK Images; 3 DK Images; 4 (L)DK Images, (C)DK Images, (R)DK Images; 5 (T)DK Images, (B) Natural History Museum/DK Images; 6 Carey B. Van Loon; 7 (L)Phil Degginger/Getty Images; (R)DK Images; 8 (T)Colin Keates/Courtesy of the Natural History Museum, London/DK Images, (B)Judith Miller/Freemans/DK Images; 9 Colin Keates/Courtesy of the Natural History Museum, London/DK Images; 10 Royalty-Free/Corbis; 11 (L)John Anderson/Animals Animals/Earth Scenes; 11 (R)Lester Lefkowitz/Corbis; 13 (TR)DK Images, (BR)Harry Taylor/DK Images, (BL)Dr. Marli Miller/Visuals Unlimited; 14 (BL)DK Images; 15 (TR)DK Images 15 (TL)Colin Keates/Courtesy of the Natural History Museum, London/DK Images, (B)DK Images; 16 James J. Stachecki/Animals Animals/Earth Scenes; 17 Dr. Marli Miller/Visuals Unlimited; 18 Gregory G. Dimijian, M. D./Photo Researchers, Inc.; 19 (TR)DK Images, (TL)DK Images; 20 (T)DK Images, (B)Andrew J. Martinez/Photo Researchers, Inc.; 21 (T)DK Images, (C)DK Images

ISBN: 0-328-23556-3

Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to anyprohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,mechanical, photocopying, recording, or likewise. For information regarding permission(s), write toPermissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

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by Trish West

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2What are minerals?Mineral Crystals

You use minerals every day. Minerals are natural, nonliving solid crystals that make up rocks.

Each mineral has the same chemical makeup. Quartz has the same chemicals whether it is found in Australia or California.

Scientists have found more than 3,000 minerals. Just a few of them make up most of the rocks in Earths crust. Most rocks contain combinations of minerals. Each type of rock always has the same combination. Granite is always made up of quartz and feldspar crystals.

Quartz

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Properties of MineralsScientists identify a mineral by testing its properties.

Now you will learn about several mineral properties.

ColorA mineral can be different colors. Different minerals

can be the same color. This makes it hard to identify a mineral by its color. Other properties are better for identifying minerals.

LusterLuster is the property of how a mineral refl ects

light. A glassy luster is shiny. A metallic luster looks like polished metal. A mineral with a soft shine can have a waxy, silky, or pearly luster. Some minerals have dull, chalky luster. Others have a greasy luster.

Satin spar gypsum

Galena

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1051

4

HardnessThe hardness of minerals varies. Scientists fi nd

out a minerals hardness by testing how hard it is to scratch. They use the Mohs scale to compare the hardness of different minerals. The Mohs scale ranks minerals from 1 to 10. Talc, with a hardness of 1, is the softest mineral. Diamond with a hardness of 10, is the hardest mineral.

A mineral can scratch any other mineral that has a lower number on the Mohs scale. You can also use other objects to scratch minerals. A penny has a hardness of about 3. A fi ngernails hardness is about 2.5. A steel fi le is about 6.5 on the scale.

Talc is not hard. Apatite is somewhat hard. Diamond is very hard.

Talc Apatite Diamond

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StreakStreak is the color of the powder that a mineral

leaves when it is scratched across a special plate. Each sample of a mineral always has the same color streak.

Crystal ShapeYou can identify a mineral by looking at its crystals.

Scientists group crystals into six basic types. For example, the crystals of fl uorite are cube-shaped.

CleavageMost minerals break into patterns. Those that break

along smooth, fl at surfaces have cleavage. Minerals that do not have cleavage may splinter like wood.

Hornblende breaks along fl at, smooth surfaces. This is its cleavage.

The streak of cinnabar is bright red.

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6GoldCalifornias state mineral is gold. Golds luster is

shiny and metallic. Its color and streak are both yellow. Gold is soft, so it can be pounded into shapes or sheets.

Other Properties of MineralsThere are other ways to identify minerals. Some

minerals may be attracted by a magnet. Minerals may feel sandy, sticky, powdery, or smooth. Some minerals can be shaped or cut. There are minerals that may smell like rotten eggs or garlic. And chemical tests can be used to identify some minerals.

Vinegar fi zzes when placed on limestone that has calcite. Carbon dioxide gas rises from the limestone.

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How are minerals and ores sorted?Resources in Rocks

Rocks can contain valuable resources. An ore is a rock rich in valuable minerals that can be removed from Earths crust. People mine ore for its minerals. Zinc and copper are two metals found in mineral ores.

Iron ore contains the metal iron. Miners dig up the iron ore. They crush and heat it. This separates the iron. Iron mixed with other materials makes steel.

Another mineral resource is gypsum. It is used in plaster and paint. Paint also contains the mineral mica. Minerals such as sylvite are used in fertilizers.

Some ores lie deep under Earths surface. Workers use machines to dig them out.

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8HematiteIron often comes from the mineral hematite.

About seven-tenths of hematite is pure iron. The rest is oxygen. Hematite may have shiny six-sided crystals. These crystals can be gray. Hematite can also have coarse grains. These grains are reddish brown. Red hematite is used to make red paint. It is also used to polish glass.

Hematite is found in California. It has been found in rocks near silver mines. Red soil can be a sign of hematite.

Iron from the mineral hematite is used to make steel.

This park bench is iron.

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GalenaThe mineral galena contains the metal lead.

Galena is gray. It has a metallic luster. It is the most common mineral that contains lead. Galena is easy to mine. People have mined galena to get lead for about 5,000 years.

California has two important sources for galena. There is a galena mine in Tuolumne County. There is also a source of galena near Darwin, in Inyo County.

Galena is mined in parts of California. It is an important source of lead.

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LeadLead is a metal. It is dense and blue-gray. Lead

seems heavy compared to similar amounts of other metals. Lead can be shaped and pulled into thin wires. It is used in building materials. Lead was also used to color paints and pottery in the past. The pieces of colored glass in stained-glass windows are held together with lead.

Years ago, lead pipes carried drinking water to buildings. Lead was also used in glassware that held food. But scientists found that lead can poison people. So lead is no longer used for these purposes.

Lead aprons protect people while they are having X-ray pictures taken.

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CopperPeople fi rst used copper thousands of years ago.

Copper is a shiny metal. It is easy to shape and is often used to make wire.

Copper is often found as a pure metal in rocks that formed from lava. Copper is also found in other minerals and ores, such as chalcocite.

Copper is good at conducting heat and electricity. It is used to make motors and generators. Bronze and brass are made from a mix of copper and other metals.

Copper is found in many parts of California. One of the largest copper mines is in Utah.

Copper is used for pipes.

The Statue of Liberty is covered with copper. Copper can turn green in damp weather.

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Using Properties to Identify MineralsScientists use a table like the one below to identify

minerals. You can use it to fi nd the names of the minerals pictured on the next page.

Mineral Color Luster Hardness Streak

Calcite

colorless or white,

pink, yellow, greenish,

or red

ranges from glassy

to dull3 white

Feldspar

colorless or many colors,

such as beige, pink, gray, and bluish

green

glassy or pearly

6-6.5 white

Hornblendedark green

to blacksilky 5-6 none

Magnetite blackshiny or metallic

5.5-6 black

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This minerals hardness is much less than that of the other minerals listed.

This minerals luster is shiny and metallic.

This mineral does not make a streak.

This mineral can have a beige color.

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How are rocks classifi ed?Igneous Rocks

Rocks can be classifi ed by the way they are formed. Igneous rocks form from molten rock. This molten rock is called magma. Igneous rocks dont have layers. However, they may have crystals that interlock.

Lava Cooling QuicklyWhen magma reaches Earths surface, it is called

lava. Lava is cooled by water or air. Often, only very small crystals have time to form. Basalt is an igneous rock cooled in water. Many islands are made of basalt. Pumice is an igneous rock cooled in air.

Obsidian forms from lava that cools quickly. It looks like glass.

Basalt is a very common igneous rock. It makes up most of the ocean fl oor.

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Magma Cooling SlowlySome igneous rocks form slowly. As magma rises

toward Earths surface, it can force open cracks. Sometimes it melts some of the rocks around it. This magma cools slowly. The slow cooling causes large crystals to form. Eventually the magma hardens into igneous rock. Sometimes this takes millions of years.

Granite forms in the way you just read about. It has large crystals of quartz, feldspar, and mica. Pegmatite and gabbro are also rocks that form this way.

An igneous rock such as granite is very hard. It can be used for buildings. Concrete in sidewalks might also contain pieces of igneous rocks.

Granite Pegmatite

Gabbro

Slow-Cooling Igneous Rocks

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Sedimentary RocksSedimentary rocks form when layers of sediments

settle on top of one another and harden. Sediments are made up of soil, shells, pieces of rock, and dead plants and animals.

Water, wind, ice, and gravity move sediments around. The sediments settle in layers on land or on the bottoms of oceans, rivers, and lakes.

LayeringNewer layers press down on older ones. Their

weight and sticky clay minerals hold the rock particles together. Natural chemicals can also bind them.

Each new layer of sediment settles on top of older layers. When scientists fi nd fossils, they can tell that the fossils in lower layers are probably older.

Layers of sedimentary rocks formed these cliffs.

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Types and Uses of Sedimentary RocksLimestone is one kind of sedimentary rock. It can

form from the hard skeletons and shells of sea animals that died long ago. It is used to make cement and glassware.

Sandstone is another kind of sedimentary rock. It can form from tiny pieces of mineral or rock. Houses and statues are often made from sandstone.

There are also sedimentary rocks that form from tiny particles. The particles settle at the bottoms of lakes or oceans. Two examples are shale and mudstone. Shale is useful in making cement.

Limestone is very heavy. The limestone you see below is in a building frame.

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Metamorphic RockHeat and pressure deep inside Earth can change

rocks. When this happens, metamorphic rocks form. Metamorphic rock can form from sedimentary rocks or igneous rocks. It can even form from other metamorphic rock.

When metamorphic rocks form, they might have crystals of a different shape or size. Sometimes new types of minerals are formed too.

Metamorphic rock is usually hard. Heat and pressure can cause it to form in layers. These layers can chip into fl at sheets and slabs. The picture on this page shows rough layers of gneiss formed by high pressure. The fi ne, thin layers of slate formed under low pressure.

The metamorphic rocks in this picture were once limestone and sandstone.

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Uses of Metamorphic RockMetamorphic rock is used in many buildings. Slate

was once used to make waterproof roofs. Chalkboards were also made from slate. Today it is used in patios and walkways. Buildings and sculptures have been made from marble for thousands of years. Marble is a good material for carving or making statues. It does not break easily. Floor tiles, stone walls, and gravel also come from metamorphic rocks.

Phyllite Slate

Gneiss

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How do rocks change?The Rock Cycle

New rocks are always being formed. At the same time, other rocks are being destroyed. The recycling of old rock into new is an ongoing process called the rock cycle. Follow the arrows on these two pages to see how rocks can change.

This granite is an igneous rock with large grains.

Granite forms when magma cools slowly. High heat and pressure change its particles. The granite turns into a metamorphic rock called gneiss.

This gneiss was once granite.

Rain and wind carry away tiny particles of the gneiss. The particles form layers that harden into sedimentary rock. Shale may be formed. Shale has thin layers of tiny particles.

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This shale is formed at the bottoms of oceans and lakes.

Heat and pressure can change shale into a much harder rock called slate. The heat and pressure destroy the shales fossils. Slate splits easily into layers.

This slate was once shale.

Heat and pressure can change slate into phyllite. Phyllite can change again to a metamorphic rock called schist. Schist has larger grains than phyllite or shale.

This schist was once slate.

The rock cycle may not end here. Schist deep inside Earth can get hot and melt. It may cool and become a new igneous rock, such as granite.

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How Rock Can ChangeAll three types of rock can change into another

type. But not all rocks complete the cycle. Rocks deep in Earths crust may not get to the surface. Sedimentary rock can melt and change into igneous rock. But it might not become metamorphic rock. Because all three types of rock can change from one type to another, the rock cycle diagram can be drawn in different ways.

Igneous rock forms from magma.

The rock cycle can start over when metamorphic rock melts into magma.

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Igneous rock can wear down into sediment, which hardens into sedimentary rock.

Sedimentary rock can change into metamorphic rock.

Metamorphic rock can melt into magma.

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cleavage property of minerals that break along smooth, fl at surfaces

igneous type of rock that forms from molten rock

luster property of a mineral that describes how the mineral refl ects light

metamorphic type of rock formed when heat and pressure change the properties of rock

mineral a natural, nonliving, solid crystal that makes up rocks

ore a rock rich in valuable minerals that can be removed from Earths crust

rock cycle the process that recycles rock into new types of rock

sedimentary type of rock that forms when layers of sediments settle on top of one another and harden

streak the color of the powder that a mineral leaves when it is scratched across a special plate

Glossary

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What did you learn?1. What kind of material makes up rocks?

2. What are three of the properties that a scientist can use to identify a mineral?

3. Why did people stop using lead for pipes and glassware?

4. In your own words, write a summary

of pages 20 and 21. First, write the most important idea from the two pages. Then write some important details.

5. Compare and Contrast Use the details on pages 8 and 9 to compare and contrast hematite and galena. How are they alike? How are they different?

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