3 7 the rocks and soils beneath us (earth science)

Vocabulary decay igneous rock loam metamorphic rock mineral nutrient rock sedimentary rock soil Picture Credits Every effort has been made to secure permission and provide appropriate cr

Trang 1

Scott Foresman Science 3.7

Nonfi ction Compare and

Contrast

• Captions

• Diagrams

• Labels

• Glossary

Rocks and Soil

ISBN 0-328-13827-4

ì<(sk$m)=bdichc< +^-Ä-U-Ä-U

Scott Foresman Science 3.7

Nonfi ction Compare and

Contrast

• Captions

• Diagrams

• Labels

• Glossary

Rocks and Soil

ISBN 0-328-13827-4

ì<(sk$m)=bdichc< +^-Ä-U-Ä-U

Trang 2

1 Which kind of rock forms in layers?

2 What are three ways that minerals

are described?

3 What are some ways minerals help

you to stay healthy?

read about metamorphic rock Write

to explain how metamorphic rock forms from limestone, based on what you have read

does soil with a lot of clay compare

to soil with a lot of sand?

What did you learn?

Vocabulary

decay

igneous rock

loam

metamorphic rock

mineral

nutrient

rock

sedimentary rock

soil

Picture Credits

Every 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.

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

Opener: Getty Images; 2 Getty Images; Backgrounds: Getty Images.

Scott Foresman/Dorling Kindersley would also like to thank: 2 (CR), 8 (CR, BC), 9 (CL, BR),

12 (CR) Natural History Museum, London/DK Images.

ISBN: 0-328-13827-4

This publication is protected by Copyright, and permission should be obtained from the publisher prior to any

prohibited 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 to

Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by L L Owens

Trang 3

Rocks Are Everywhere

Rocks are solid objects that come in all

different shapes and sizes Have you ever wondered

what our planet’s rocks are made of? Rocks are

made mostly of minerals A mineral is a natural

substance that is made of nonliving matter

Rocks have different colors and textures

depending on the minerals in them A rock

can be made of just one mineral

or of many different minerals

A rock’s texture is the

size of the bits of minerals,

or grains, within it A rock’s

color depends on the kind

of minerals and other

substances that are in the rock

Granite

2

Shape, color, and texture can indicate rock type.

Groups of Rocks

Scientists group rocks by their color, texture, and minerals Rocks are also grouped by how they formed

Igneous rock comes from a mixture of

melted minerals and gases deep inside the ground This blazing hot mixture cools and hardens as it moves toward the surface If the solid rock cools quickly, its mineral grains can

be large But if the solid rock cools slowly, its mineral grains can be too small to see

3

Trang 4

One kind of igneous rock is obsidian

Obsidian is dark, smooth, glassy, and very hard

It forms when melted rock cools very quickly

It can be used to make tools Some obsidian stones

have white designs on the surface where crystals

formed The designs look similar to snowfl akes

Those rocks are called snowfl ake obsidian

Obsidian

Snowfl ake

obsidian

4

When water travels over the land, it picks up small bits of broken rock When these bits of rock settle on the bottom of lakes, rivers, and oceans, they are called sediment Over thousands

of years, pressure can bind bits of sediment together

This turns the sediment

into sedimentary rock

The remains of dead plants and animals can be buried under layers of sedimentary rock After many years, these remains can turn into stone Then the remains are called fossils

Fern fossil

Fish fossil

The cliffs of the Grand Canyon,

in Arizona, show layers of sedimentary rock.

5

Trang 5

Examples of Metamorphic Rock

The third rock group is called metamorphic

rock Metamorphic rock is igneous or

sedimentary rock that has changed over a long

time into a new kind of rock Limestone is

a sedimentary rock Limestone becomes marble

when it is heated and pressed for many years

Marble is a metamorphic rock often

used in building

Slate

Marble, a metamorphic rock, is often used to make fl oors.

6

Where Rocks Form

When rocks melt, they mix, cool, and harden

to form new igneous rock When rocks are worn down, the remains form new sedimentary rocks

Under the right conditions, both igneous and sedimentary rocks can become metamorphic rock

Lava cools to form igneous rock on the slopes of volcanoes Rock particles are carried

by rivers into the sea, where they form sedimentary rock.

Under pressure, igneous and sedimentary rock can form metamorphic rock.

7

Trang 6

More About Minerals

Minerals are the most common solid material on

Earth Almost everything we use contains minerals

Scientists can tell minerals apart by looking at

things such as color, streak, hardness, and luster

Color is the easiest to notice Some minerals come

in different colors Spinel, for example, is a mineral

that can be red, lavender, blue, green, brown,

or black The most common variety of

spinel is a clear red

Red spinel

Quartz

Spinel

The minerals

quartz and spinel

cling to this rock.

8

Streak is the color of the mineral in its powder form You can fi nd a mineral’s streak

by rubbing the mineral across a hard surface

The color of a mineral’s streak is always the same This is true even if the mineral itself comes in different colors

Pyrite is a mineral It is called “fool’s gold”

because it is often confused with gold Pyrite’s streak is black Real gold has a yellow streak

Pyrite Gold

Molybdenite

Molybdenite streak

9

Trang 7

Platinum

Amethyst

Hardness is how easily

a mineral can be scratched

Hardness is measured on

a scale of one to ten One

is the softest and ten is the hardest The hardest mineral

is diamond It cannot be scratched by anything but another diamond

Luster describes how

a mineral refl ects light

Gold, platinum, and silver are all minerals with a metal-like luster The most common luster is glassy

Amethyst has a glassy luster

10

Minerals in Our Lives

We depend on minerals When you turn

on a lamp, you are using copper, quartz, and wolframite The copper is in the electrical wiring

Quartz is found in the glass of the lamp’s bulb

Wolframite is in the metal wire of the bulb

Anything made of glass has quartz in it

You will fi nd quartz in drinking glasses, TVs, radios, and clocks Quartz is one of the most common minerals on Earth

Quartz

Wolframite

Copper

The wires inside a light bulb are made with wolframite The bulb’s glass contains quartz.

Electrical wires are made of copper.

11

Trang 8

To stay healthy, your body needs minerals

every day! When you sprinkle salt on food,

you are using the mineral halite The iron in

meat helps your red blood cells Chromium

is a mineral that may help prevent a disease

called diabetes

Calcium and magnesium are important

minerals for your body Calcium builds bones

and teeth Magnesium helps muscles tighten

and relax

Halite, or salt

Calcium carbonate, or chalk

Toothpaste contains

calcium carbonate.

Salt

12

From Rocks to Soil

Soil is the thin layer of loose material that

covers most of the land on Earth Plants, animals, and people all depend on soil

Soil is made up of water, air, bits of rock, and

nutrients Nutrients are materials that plants need

to help them grow Some nutrients are the remains

of living plants and animals that have broken down

through a process called decay Other nutrients

come from the minerals in the soil

Rabbits depend on soil for food and shelter.

13

Trang 9

Kinds of Soil

Soil forms in layers The top

layer is called topsoil It contains

many nutrients Below the

topsoil is subsoil, where

tree roots fi nd their water

The deepest layer is bedrock

As bedrock gets broken

down, it becomes soil

Humus is found in soil

It is made of decaying

plants and animals

Clay is made of small

particles Clay soil is thick,

dense, and traps water

Sand particles are large and

have a lot of space between

them Water passes through

sand Silt has medium-sized

particles It lets the right

amount of water in and out

Humus

Subsoil

Poor soil with rock fragments Topsoil

Bedrock

14

Loam is a kind of soil

made of sand, silt, and clay

Crops usually grow best in loam because it has the right amount of sand, silt, and clay

Rocks, minerals, and soil are everywhere Without rocks, minerals, and soil, we wouldn’t

be able to live So be sure to treat the earth beneath you well!

Loam

15

Trang 10

Glossary

the remains of living matter into nutrients

igneous rock rock that forms when hot,

melted minerals in the center

of Earth cool down

very well in and that contains sand, silt, and clay

metamorphic rock that forms when igneous

by heat or pressure

from nonliving matter

nutrient material that plants and animals

need to live and grow

are found in and on Earth

sedimentary rock that forms when layers of

soil the thin layer of loose material that

covers most of the land on Earth