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Minerals, Rocks, and Soil

A Science A–Z Earth Series

Word Count: 1,748

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Written by Rachel Kamb

Minerals, Rocks,

and Soil

Minerals, Rocks, and Soil

Written by Rachel Kamb

www.sciencea-z.com

Minerals, Rocks, and Soil © Learning A–Z Written by Rachel Kamb

All rights reserved.

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Key elements Used in this BooKthe Big idea: Earth is made up of various living and nonliving materials. Elements form minerals, and minerals form rocks. Each mineral and rock can be classified in many ways. Igneous, sedimentary, and metamorphic rocks form differently and can transform through the rock cycle. Through weathering and erosion, rocks change, break, and move. Minerals mix with organic material, forming the soil on which plants and animals rely. People use nonliving materials as resources by mining, drilling, and refining them. While seemingly abundant, Earth’s resources are limited and must be preserved for future generations. Key words: bedrock, crystal, deposit, drill, element, energy resources, erosion, fossil, humus, igneous rock, inorganic, lava, magma, matter, metal, metamorphic rock, mine, mineral, ore, organic, process, raw material, refine, resources, rock, rock cycle, sedimentary rock, soil, subsoil, topsoil, weathering

Key comprehension skill: Main idea and detailsOther suitable comprehension skills: Compare and contrast; classify information; cause and effect; identify facts; elements of a genre; interpret graphs, charts, and diagrams; using a glossary and boldfaced terms; using a table of contents and headings

Key reading strategy: Connect to prior knowledgeOther suitable reading strategies: Ask and answer questions; summarize; visualize; retell

Photo Credits: Front cover (tl): © iStockphoto.com/Gilles Glod; front cover (tc), pages 7, 8 (3), 20 (tr, cl): Casey Jones/© Learning A–Z; front cover (tr): © iStockphoto.com/malerapaso; front cover (cl): © iStockphoto.com/ Martin Novak; front cover (c): © iStockphoto.com/Jakub Krechowicz; front cover (cr), page 8 (1): © iStockphoto.com/ Fabrizio Troiani; front cover (bl): © Igor Baz/123RF; front cover (bc): © iStockphoto.com/Jacob VanHouten; front cover (br): © iStockphoto.com/Jill Fromer; front cover (background): © iStockphoto.com/Selahattin Bayram; back cover, page 8 (4): © iStockphoto.com/Jodi Jacobson; title page: © iStockphoto.com/Agnes Csondor; page 3: © iStockphoto.com/hsvrs; page 4: © iStockphoto.com/Jason Floyd; page 5 (top): © Jelena Zaric/123RF; page 6 (top): © iStockphoto.com/Don Wilkie; page 6 (b): © iStockphoto.com/Rainer Walter Schmied; pages 8 (2), 20 (tl): Doug Tepper/© Learning A–Z; page 8 (5): © iStockphoto.com/Nikola Miljkovic; page 8 (6): © iStockphoto.com/Max Delson Martins Santos; pages 8 (7), 10 (t): © iStockphoto.com/stockcam; page 8 (8): © iStockphoto.com/Anandha Krishnan; page 9: © DK Images; 10 (t): © O. Diez /Arco Images GmbH/PhotoLibrary;

page 10 (bl): © iStockphoto.com/Ross Chandler; pages 10 (br), 14 (tl): © iStockphoto.com/Sean Curry; pages 11 (t), 13 (b),14 (tr): © iStockphoto.com/Tyler Boyes; page 11 (b): © iStockphoto.com/Stephen Morris; page 12 (t): © iStockphoto.com/clu; page 12 (c): © iStockphoto.com/Chanyut Sribua-rawd; page 12 (b): © iStockphoto.com/Daniel G. Mata; pages 13 (t), 16 (l): © Jupiterimages Corporation; page 14 (b): © iStockphoto.com/Kime Veruss; page 15 (t): © iStockphoto.com/Radu Razvan; page 15 (b): © iStockphoto.com/Tom Mounsey; page 16 (r): © iStockphoto.com/Thierry Roy; page 17 (tl): © iStockphoto.com/Valeriy Novikov; pages 17 (tc), 20 (cr): © iStockphoto.com/Mark Wragg; page 17 (tr): © iStockphoto.com/Thomas Osborne; page 17 (b): © iStockphoto.com/Geoff Hardy; page 18 (t to b: 1, 2): © iStockphoto.com/Bart Coenders; page 18 (3): © iStockphoto.com/Barıs5 Muratoglu; page 18 (4): © iStockphoto.com/Kadir Barcin; page 18 (5): © iStockphoto.com/AdShooter; page 19: © Design Pics Inc./Alamy; page 21 (l): © iStockphoto.com/Taylor Hinton; page 21 (r): © iStockphoto.com/ hh5800; page 22 (l): Gawain Douglas/© Learning A–Z; page 22 (r): © iStockphoto.com/Morgan Lane Studios

illustration Credits: Pages 5 (bottom), 20 (bottom): Casey Jones/© Learning A–Z

Introduction

Earth provides everything you need to stay alive. It has water for drinking and air for breathing. It is home to plants and animals, which you need for so many reasons. But don’t forget one more important thing Earth provides: land!

The land is where you walk and where you play. Your home is built on land. But what is land made of? Why is it important? In this book, you will learn about nonliving Earth materials that make up the land.

Nonliving Earth materials differ a lot from one place to another. They come in many colors, shapes, and sizes, and can change quite a bit. They also help you in ways you may not realize.This home and the land it sits on are

made of nonliving Earth materials.

3 4

Table of Contents

Introduction ........................................................ 4

Elements and Minerals ...................................... 5

Rocks .................................................................... 7

Rock Groups ....................................................... 9 Igneous Rocks ................................................... 9 Sedimentary Rocks .......................................... 11 Metamorphic Rocks......................................... 13

The Rock Cycle ................................................. 14

Weathering and Erosion .................................. 15

What Is Soil? ..................................................... 17

Kinds of Soil ...................................................... 18

Layers of Soil ..................................................... 19

Using Earth’s Resources .................................. 21

Conclusion ........................................................ 22

Glossary ............................................................. 23

Index .................................................................. 24

Sr

Darmstadtium

DsRoentgenium

RgCopernicium

CnFlerovium

FlLivermorium

Lv

Cesium

Cs

Elements and Minerals

To start thinking about what Earth is made of, let’s start small . . . really small. Elements are what make up all matter, both living and nonliving. Everything on Earth is made from just over one hundred different elements. Carbon, helium, and zinc are a few of these elements.

5 6

Silver is a mineral made of one element.

A mineral is a natural substance made of elements. Some minerals, including many kinds of metal, consist of just one kind of element. For example, silver is only made of silver, and iron is only made of iron. Many other minerals consist of two or more elements. For example, quartz is made of the elements silicon and oxygen. Earth has nearly 4,000 different minerals. Each one has its own mixture of elements.

All minerals are solid, and they form in a pattern of crystals. Minerals have crystals because their atoms are arranged in tidy patterns. Different patterns make different crystal shapes. Minerals are also inorganic. This means they are not living, and they were never alive.

elements → minerals → rocks

Quartz is made of two elements. Can you see the pattern made by the minerals?

Elements are not the smallest parts of matter. The tiniest bits of each element are called atoms.

This table lists all the known elements on Earth. Each box has a symbol for the element and more information about it.

elements → minerals → rocks

Periodic table of the elements

7 8

Rocks

What happens when minerals combine? A rock is a hard, solid material found in nature. Most rocks are made of different minerals, just as a salad is made of different vegetables. If you pick up a rock, you might see several colors and patterns. These are usually bits and pieces of different minerals. The mix of minerals in one kind of rock helps you tell it apart from other kinds of rocks.

You can describe a rock in many ways. You can also compare one rock with another. Read the chart to learn some ways to describe and compare rocks.

how to describe and comPare rocks

elements → minerals → rocks

Each rock is made up of a certain mixture of minerals.

mineral composition

rocks have a special mixture of one or more minerals.

Sizerocks can be huge boulders or small pebbles. they can be as big as a mountain or as tiny as a speck of dust.

Shape rocks can be flat, round, square, or almost any other shape.

Colorrocks come in every color you can imagine. many rocks have more than one color, depending on the colors of their minerals.

Texturesome rocks feel very rough, while others are smooth. they can have tiny grains; large, smooth chunks; or long, pointed crystals. some rocks are full of airholes.

Hardnessthe mohs scale of hardness compares how hard each mineral is within a rock. talc is rated a 1 (very soft), and diamonds are rated a 10 (very hard).

Patternsrocks may have streaks, waves, or straight lines. they may have dots everywhere or be built layer upon layer. some rocks do not have a clear pattern.

Locationan important way to describe a rock is by where in nature it is found. a beach may have different rocks than a forest, desert, or volcano.

To remember how igneous rocks form, think of the word ignite, which means “to start a fire.” Igneous rocks start off very hot and then cool down.

Rock Groups

When you think of “rock groups,” you might imagine loud music. But Earth has its own kinds of rock groups. Every rock belongs in one of three groups, based on how it formed. Let’s take a closer look at each rock group and how it forms.

Igneous Rocks Boom! A volcano blasts hot, liquid rock, called magma, from beneath Earth’s crust. The magma, which is called lava above the ground, cools on the surface, making igneous rocks (IG-nee-us). Other igneous rocks form as magma cools underground.

9 10

Igneous rocks can be very different from one another. The size of the crystals in an igneous rock is determined by how fast the magma cools and turns solid. If lava cools quickly on the surface, it does not have time to grow large crystals. For example, pumice is a rock that cooled quickly. It is made of tiny glass crystals.

When magma cools slowly underground, the extra time allows larger crystals to form. Granite, which cools slowly, is hard and very solid. It has large crystals made of several minerals.

Granite is used for kitchen counters and in the walls of some buildings.

lava igneous rocks

Volcano

magma

Obsidian forms when magma cools very quickly. It looks like black glass.

Pumice is full of tiny airholes. It’s so light that it can float in water!

Look for fossils where ancient oceans, lakes, or rivers used to be. A fossil can help you learn about what once lived in an area. You can also compare those plants and animals with the ones that live there today.

Fossils may be found in sedimentary rocks. Millions of years ago, dead plants and animals settled at the bottom of lakes, rivers, and seas. Over time, layers of sediment buried the plants and animals, forming sedimentary rocks. The plants and animals, or imprints of them, sometimes hardened and remained in the rock. These are fossils.

11 12

Sedimentary Rocks Some rocks are made from tiny bits of minerals called sediment. Because sediment is so small, water and wind can easily move it and deposit it in different locations. Sediments can build up, layer upon layer. Older sediments at the bottom become compacted as newer layers build up above them. Over a long period of time, all that weight and pressure create sedimentary rocks.

Sedimentary rocks are often the easiest rocks to break apart. They are made up of bits of rock that have been pressed together, not melted together like igneous rocks. Some sedimentary rocks, such as sandstone, can crumble when you walk on them. But others are strong.

Coal is a sedimentary rock mostly made of the element carbon, which is found in living material. Over millions of years, pressure turned the living material into rock.

When you look at a side view of sedimentary rock layers, you are seeing a slice of history.

fossilized leaf

fossilized dinosaur footprint

Breccia is a type of sedimentary rock.

13 14

Metamorphic Rocks Metamorphic rocks (met-uh-MOR-fick) form when a rock changes due to heat and pressure. Igneous, sedimentary, and metamorphic rocks can all end up deep below Earth’s surface. There, Earth’s heat and the pressure caused by the heavy rocks above them makes them change more.

A sedimentary rock can be very weak. But after it has been heated and placed under additional pressure, it can become a metamorphic rock, such as marble. Marble is very strong, so it is often used in buildings and statues.

The word metamorphic comes from the Greek word metamorphosis, which means “to change.” How are a butterfly and a metamorphic rock alike?

The Rock Cycle

Plants and animals change during their life cycle. Water changes as it moves through the water cycle. Rocks change, too. In fact, any of the three kinds of rocks can change into one of the other kinds. The rock cycle describes the process that rocks go through as they change from one kind to another. Study the diagram to learn how any kind of rock can change into any other.

Phyllite (left) and gneiss (right) are two examples of metamorphic rocks.

the rock cycle

igneous rock

sedimentary rock

metamorphic rock

w

eathering and erosion

heat

and

pre

ssur

e

melting

melting

heat and pressure

wea

ther

ing

and

eros

ion

15 16

An arch caused by weathering A rockslide caused by erosion

Weathering and Erosion

Rocks can also change without becoming a new kind of rock. They can change shape or size. They can also move from one place to another.

Weathering makes rocks change. Sometimes they change shape or size. Wind and water make rocks bang into each other. They might become smooth and round or break into pieces. Water can seep into cracks in a rock and freeze, breaking the rock. A plant’s roots might grow into a crack in a rock. As the crack expands, pieces of the rock may break off.

The chemicals in rocks can change, too. Minerals may fall apart or dissolve when they mix with water or other chemicals. Acid from plants can change rocks, too. When a rock’s chemicals change, it may get weak or crumble.

Weathering changes rocks, but erosion moves them to a new place. Forces such as wind and water carry the loose pieces of rock and deposit them somewhere else. As some rocks move, they create more erosion by making other rocks move. Large boulders can break into smaller rocks, stones, pebbles, sand, or even dust.

Other forces cause erosion, too. Moving ice in a glacier slowly carries loose rocks downhill. Earthquakes or heavy rain can cause landslides, in which loose rocks tumble due to gravity. People can cause erosion by using machines to cut through rock and haul it away. Even wildfires can cause erosion by removing the vegetation that holds rocks in place.

A tree is splitting a rock. This is an example of mechanical weathering.

Acid rain has changed the minerals in this gravestone. This is an example of chemical weathering.

organic matter

soil

ro

cks and minerals

17 18

Kinds of Soil

There are thousands of kinds of soil around the world. Each one is made up of a unique combination of minerals, bits of rock, and organic material.

It can take hundreds or thousands of years for each kind of soil to form. Because of all the possible mixtures, soil comes in many colors and textures. Some soils are dense, or packed together tightly. Others are packed more loosely.

What Is Soil?

Earth isn’t just covered with broken rocks and minerals. The land also has a lot of organic matter. This material is living or once was alive. It includes rotting plants, dead animals, and animal waste. The mixture of rocks, minerals, and organic matter is called soil.

Soil also contains air between all the bits of solid material. Most soils contain some amount of water, too.

The organic matter in soil is called humus (HYOO-muss). It is full of nutrients. Plants rely on the air, water, and nutrients in soil to grow and to live. Many animals eat those plants. So you have soil to thank for the foods you eat.

Soil scientists have identified over 10,000 different kinds of soil in Europe alone.

Layers of Soil

Just like rocks, soil changes and moves. Weathering and erosion affect soil most on the surface. As a result, soil often forms in different layers.

The thin layer found on most of Earth’s land is called topsoil. It is often soft and rich in organic material. It usually contains more air and water than the deeper layers.

The middle layer is called subsoil. It tends to be drier and harder than topsoil and contains more rocks.

Bedrock is usually far below the surface. Here, weathering and erosion have not changed the rock much. Less water and air can reach it, so bedrock is often very hard and dry.

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One good way to describe soil is by its texture. Scientists also measure how compact, or pressed together, the soil is. They describe the soil’s color and temperature, too. They may even find out how much water, air, and humus it contains.

Sand feels gritty, while silt is made of smaller bits and feels powdery like flour. Clay is made of even smaller bits mixed with water, so it feels sticky. Loam is a mixture of sand, silt,

clay, and organic matter.

In the last 200 years, the United States has lost from 25–70 percent of its

topsoil due to farming, logging, and grazing. With fewer plants, soils have been eroded by wind and water and have washed down rivers and streams.

Science In Your World

Science In Your World

sand silt

clay loam

n low n moderate n high n Very high

toPsoil loss Per year in the United states

cUtaway View of soil layers

topsoil

subsoil

bedrock

21 22

Using Earth’s Resources

We use gravel for roads, tiles for floors, and oil for energy. We use bricks for buildings, glass for windows, and metal for cars. When we use Earth’s materials, we call them resources. Some resources are deep below Earth’s surface. To reach them, people mine, dig, drill, or blast into the land.

Most of Earth’s resources cannot be used in their natural form. These raw materials have to be processed or refined. For example, most metals are found mixed with other minerals in a rocky substance called ore. Machines process the ore to sort the metals, such as copper and silver. They also remove unwanted minerals. Coal and oil are important energy resources. Factories refine them before they can power our cars and heat our homes.

Conclusion

Elements make up minerals, and minerals make up rocks. Rocks form in different ways. They can be igneous, sedimentary, or metamorphic. Over time, each kind of rock can change into one of the other kinds.

Weathering and erosion make rocks change and move. As rocks break down, they can mix with organic matter to form soil. Earth has countless kinds of rocks and soils. Plants and animals rely on healthy soil.

People use Earth’s resources to make and build things. Some resources are in limited supply, so it is important that we use Earth’s materials wisely.

drilling for oilmining for metals

23 24

Glossary

crystals minerals that form in regular, tight patterns (p. 6)

deposit to set down one or more layers of material in a new place, as water or wind can do to sediment (p. 11)

elements pure substances; the building blocks of everything on Earth (p. 5)

erosion the process of transporting and wearing away rocks or soil as loose particles are moved by water, wind, ice, or gravity (p. 16)

fossils the remains of plants or animals that turned to stone over a long period of time (p. 12)

igneous rocks formed by the cooling and rocks hardening of hot magma or lava

(p. 9)

metal a material, usually hard and shiny, that allows electricity and heat to move through it (p. 6)

metamorphic rocks formed when any type rocks of rock goes through changes

caused by extreme heat and pressure (p. 13)

mineral a solid, natural material that does not come from a living thing (p. 6)

resources supplies of things that are valuable or very useful to people (p. 21)

rock a hard, solid material that is made of minerals and is found in nature (p. 7)

rock cycle the series of changes that rock undergoes as it shifts between different types (p. 14)

sedimentary rocks formed when sediment is rocks pressed together over time (p. 11)

soil the top layer of the ground, in which plants grow; dirt (p. 17)

weathering the process of wearing away or otherwise changing Earth’s surface, caused by natural forces (p. 15)

Index

atoms, 5, 6coal, 12, 21humus, 17, 20lava, 9magma, 9, 10ore, 21

Periodic Table of the Elements, 5sediment, 11, 12soil layers, 19weathering, mechanical vs. chemical, 15