FOCUS ON EARTH SCIENCE (5)

Earth’s Structure
/…iÊÊ`i>
Heat escaping from Earth’s
internal layers constantly
changes the planet’s
surface.

1 1.e, 1.f, 2.a, 7.c
ˆ}
>ˆ˜
Landforms
*ˆVÌÕÀi
`i>
>ˆ˜Ê`i> Forces
LESSON

inside and outside Earth
produce,i>`ˆ˜}
Earth’s diverse

…iVŽ
landforms.

2 2.c, 6.b, 6.c, 7.e
Minerals and Rocks

LESSON

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>ˆ˜
>ˆ˜Ê`i>

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The solid
`i>

Earth is made of minerals
,i>`ˆ˜}
and rocks.

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LESSON

3

1.b, 4.c, 7.e, 7.f, 7.g

Earth’s
ˆ}
>ˆ˜ Interior
`i>

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>ˆ˜Ê`i> Earth’s
interior
has a layered
,i>`ˆ˜}

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structure.

>ˆ˜

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Now
ow
did that h
happen?
appen?
`i> how

Imagine the results of a fender bender
between
,i>`ˆ˜}two cars. The fenders of each are a crumpled mass of metal. When
two
…iVŽ
continents collide, the results are similar—the rocks become crumpled
and broken. The photo shows folded rock layers near Lulworth in the United
Kingdom. They are the result of a collision between the African and European
plates hundreds of kilometers away.

-Vˆi˜ViÊÊ+PVSOBM Describe what an auto collision might look like in slow
motion.

74
Martin Bond/Photo Researchers


Start-Up Activities

How can you model
landscapes?
Imagine you are hiking
through a natural area
such as Yosemite Valley,
California. Make a list of
the landscape features
you think you would see.

Procedure

Earth’s Layers Make the
following Foldable to show
Earth’s layers.
STEP 1 Fold a sheet of paper in half
lengthwise. Make the back edge about 2 cm
longer than the front edge.

STEP 2 Fold into thirds.

1. Identify features on your list that are the
highest and the lowest in elevation.
2. What makes each feature unique? Were
some flat, or peaked on the top?
3. Stack several pieces of artfoam in layers,
one on top of another. Put your hands on
both ends of the stack, and shape the
layered artfoam into different terrains.

STEP 3 Unfold and cut along the folds of
the top flap to make three flaps.

Think About This
• Explain What did you do to the artfoam
that might indicate how a landscape
would form in nature?
• Examine the side of the model you made.
What might the layers represent?

STEP 4 Label as shown.

1.a, 7.e

œÀi

>˜Ìi


ÀÕÃÌ

ELA6: R 2.4

Visit ca6.msscience.com to:
▶
▶
▶
▶

Clarify As you read this chapter, identify

Earth’s layers on the tabs. Under each tab,
explain the features and describe the
energy in that layer.

view
explore Virtual Labs
access content-related Web links
take the Standards Check

75
Matt Meadows


Get Ready to Read
Identify the Main Idea

ELA6: R 2.3

Learn It!

Main ideas are the most
important ideas in a paragraph, a lesson, or a chapter.
Supporting details are facts or examples that explain the
main idea. Understanding the main idea allows you to
grasp the whole picture.

Practice It!

Read the following paragraph. Draw a graphic organizer like the one below to
show the main idea and supporting details.

The wearing away of soil and rock is called erosion.
Water does most of this work. Rivers and streams
carry rock fragments as the water flows downhill.
Over long periods of time, this action changes the
landscape. Mountains are worn down to flat plains.
As rivers flow toward lakes or oceans, they carve
valleys and steep-sided canyons.
—from page 80

Main Idea

Apply It! Pick a paragraph
from another lesson of this chapter and
diagram the main idea as you did above.
76


Target Your Reading

en the
ea is oft
d
i
n
ph
i
a
The m
paragra
a

n
i
e
c
n
te
f irst sen
always.
but not

Use this to focus on the main ideas as you read the chapter.

Before you read the chapter, respond to the statements

1

below on your worksheet or on a numbered sheet of paper.
• Write an A if you agree with the statement.
• Write a D if you disagree with the statement.
2

After you read the chapter, look back to this page to see if
you’ve changed your mind about any of the statements.
• If any of your answers changed, explain why.
• Change any false statements into true statements.
• Use your revised statements as a study guide.

Before You Read
A or D

Statement

After You Read
A or D

1 Energy from the Sun changes Earth’s landscapes.
2 Earth’s internal energy pushes up the land; surface
processes wear it down.
3 Most of Earth, including its interior, is composed
of rock.
4 Hardness and color are the two main characteristics
of gems used in jewelry.
5 Matter and energy move from Earth’s interior toward
the surface.
Print a worksheet of
this page at
ca6.msscience.com .

6 Heat is always escaping from Earth’s interior.
7 Humans have drilled holes and collected samples to
about 500 km deep in Earth.
8 There is one type of crust near Earth’s surface, and it
is found on the continents.
9 The thickest of Earth’s layers is the core.
10 Seismic waves do not penetrate Earth’s layers.
77


LESSON 1
Science Content

Standards
1.e Students know major geologic events,
such as earthquakes, volcanic eruptions,
and mountain building, result from plate
motions.
1.f Students know how to explain major
features of California geology (including
mountains, faults, volcanoes) in terms of
plate tectonics.
2.a Students know water running
downhill is the dominant process in shaping
the landscape, including California’s
landscape.
7.c Construct appropriate graphs from
data and develop qualitative statements
about the relationships between variables.

Reading Guide
▼

What You’ll Learn
Classify landforms.

▼

Explain how landforms are
produced.

▼

Relate your knowledge of
landforms to California
landscapes.

Why It’s Important

Landforms
>ˆ˜Ê`i> Forces inside and outside Earth produce Earth’s
diverse landforms.
Real-World Reading Connection Imagine you’re making a
sculpture by piling up sand near the shore. Suddenly, a
wave comes and washes away part of your new artwork.
Through different and slower processes, landforms are constantly
ˆ} built up and worn down on Earth’s surface.
>ˆ˜ being
`i>

*ˆVÌÕÀi

How
do landscapes form?
,i>`ˆ˜}

…iVŽ

You live on the surface of Earth. Look out the window at
this surface, or look at a photograph or drawing of a landscape. Figure 1 is an example. There are tall mountains,
deep valleys, and flat plains. Why does the landscape have
different shapes and forms?
An endless interaction of forces reshapes Earth’s topography. The transfer of matter and energy from Earth’s interior builds mountains. Forces on the surface continuously

wear down the mountains. These forces are caused by
uneven heating of the surface by the Sun. In turn, this
energy is transferred to the atmosphere. This makes
weather that constantly bombards surface material and
erodes it away, especially in higher areas. Without these
competing forces, the planet’s surface would be a flatter
and less exciting place to live.

You’ll appreciate landforms
around you as you discover
how they form and change.

Vocabulary
landform
uplift
erosion

Review Vocabulary
weather: current condition
of the atmosphere;
temperature, wind speed and
direction, humidity, and air
pressure (Grade 5)

78 Chapter 2 • Earth’s Structure

What is the source of energy for Earth’s weather?

Figure 1

Earth’s landscape is the
result of internal and external forces
constantly acting upon the surface.


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U. S. Topography This
map shows major landform regions
in the continental United States.

Identify What landform covers much
of California?

Landforms
Features sculpted by processes on Earth’s surface are called
landforms. They can cover large regions or be smaller, local
features. Figure 2 shows the landform regions of the continental United States. These are large areas with similar topography. Find your location on the landform map in Figure 2.
Three main types of landforms are shown on the landform
map. These examples are mountains, plateaus, and plains.
Mountains and plateaus are areas with high elevations. Plains
are low, flat areas.

Landforms Made by Uplift

Uplift is any process that moves the surface of Earth to a
higher elevation. Both mountains and plateaus are formed by
uplift. If a large flat area is uplifted, a plateau is formed. If the
uplifted area is not flat, but has many steep slopes, it is called
a mountain.
Earth’s internal energy produces uplift. As thermal energy
from Earth’s interior moves toward the surface, it also causes
matter in the interior to move upward. An example of a landform moved by uplift is shown in Figure 3. Sometimes Earth’s
internal heat energy melts rocks. If this melted rock moves to
the surface, a mountain called a volcano can form. More
often, the heat does not melt the rocks but makes mountains
by pushing solid rocks upward. Scientists call the forces that
can push solid rocks upward plate tectonics, which you will
read about in Chapter 5.

Figure 3 Uplifted
Landforms Mountains and
plateaus are made by uplift.

Lesson 1 • Landforms

79


ACADEMIC VOCABULARY
transport (trans PORT)
(verb) to carry from one place
to another
A large truck was needed to
transport the cargo.

Landforms Shaped by Surface Processes
While Earth’s internal energy pushes up the land, surface
processes wear it down. As you read earlier, energy from the
Sun drives some of these processes on the surface. Water,
wind, ice, and gravity break apart the rocks that make up
mountains. These broken fragments are carried downhill,
making the mountains smaller.
The wearing away of soil and rock is called erosion. Water
does most of this work. Rivers and streams carry rock fragments as the water flows downhill. Over long periods of time,
this action changes the landscape. Mountains are worn down
to flat plains. As rivers flow toward lakes or oceans, they
carve valleys and steep-sided canyons. Figure 4 shows landforms that can form as the material is eroded and
transported by rivers.
When rivers eventually slow, they deposit some of their
load of rock fragments. The fragments are distributed by
the water to build other landforms, like the beach shown
in Figure 4. Wave action from the ocean moves fragments
of rocks, such as the sand on this beach, along the coastline.

Figure 4

Reshaped Landscapes Plains,
valleys, canyons, and beaches are made by
erosion and deposition of rock material
that once was part of uplifted landforms.

Locate areas where eroded fragments
have been deposited.

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80 Chapter 2 • Earth’s Structure


California Landforms
California has many types of landforms.
Some are so spectacular that they are preserved in state or national parks. Maybe you
have taken a trip to visit one of these parks.

Yosemite Valley
For example, the U-shaped surface of the
valley in California’s Yosemite National Park
is shown in Figure 5. Glaciers carved this
shape into the valley as they moved across its
surface about one million years ago. In contrast, rivers usually carve sharper, V-shaped
valleys as they cut through and erode rock.
How do valleys carved by glaciers
differ in shape from valleys carved
by rivers?

Lassen Peak

Another national park with landforms is
Lassen Volcanic National Park. It features an
active volcano, which is shown in Figure 5.
Lassen Peak is a volcano that is part of the
Cascade Mountain Range. A series of violent
volcanic eruptions in 1915 blasted out a new
crater at Lassen Peak’s summit. The explosion expelled melted rock, gas, and ash that
dramatically changed the landscape around
the volcano. Volcanic ash mixed with snow
and ice. This caused a rapid flow of mud
down the sides of Lassen Peak and into river
valleys below. Residents living in the vicinity
of the eruptions lost their homes.
These California landforms show how different forces can act to change the landscape.
External forces that caused precipitation for
glacial ice to accumulate shaped the landscape of Yosemite Valley. Internal forces
caused volcanic eruptions that altered the
landscape surrounding Lassen Peak.

Yosemite Valley

Figure 5

Glaciers and Volcanoes
Yosemite Valley and Lassen Peak
show how diverse the California
landscape can be.

Lassen Peak
Lesson 1 • Landforms

81


Mountains
California’s major landforms are shown in Figure 6. This
is a shaded relief map of the state. Find the Sierra Nevada and
the Coastal Ranges. These are examples of mountains formed
by the forces of plate tectonics. Solid rock was pushed up,
forming high peaks. Because the ranges are long and narrow,
they sometimes are called mountain belts.
Figure 6 Identify two landform regions to the north of
the Transverse ranges.

Now find Mount Shasta in Figure 6. It looks different from
the other mountains. In fact, Mount Shasta looks like a distinct circle on the map. Mount Shasta is a volcano. It did not
form by uplift of solid rock, as did most of the mountains in
California. Mount Shasta’s cone-shape formed when melted
rock poured out from its center onto the land surface.
California’s mountains continue to grow upward. Most
often they grow so slowly you don’t even realize this uplift is
happening. Other times a volcanic eruption or an earthquake
causes sudden uplift.

Figure 6 California Topography This map shows California’s
major landforms.
Identify the type of landform that is located between the mountain ranges.
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82

Chapter 2 • Earth’s Structure

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California
Agriculture Statistics
• California has been the top
agricultural state for more
than 50 years.
• Agriculture generates almost
$26.7 billion per year.
• Almost one-third of
California’s land area is used
for farming.

Figure 7 The particles eroded from the
mountain ranges surrounding the Central Valley have provided the soil base for producing
most of California’s agricultural products.
Valleys

• California produces more
than 350 crops.
• California grows more than
half of the United States’
fruits, vegetables, and nuts.
Source: USDA Agriculture in the Classroom

Next to the California mountain ranges are flat, open valleys. As the mountain peaks rise upward, erosion by water,
wind, ice, and gravity wear them down. Water is a powerful
force, capable of carrying loosened rock fragments and soil
particles from the mountains down to the valleys. This loose
material helps make the valley’s farmland rich in soil nutrients for growing plants.
These fertile valleys make California a top-ranked agricultural producer in the United States. Figure 7 shows a farm
located in the Great Central Valley. What is being produced
on the farm shown here?
California also has many deep, narrow valleys. Rivers carve
these valleys as they flow from the mountains toward the
Pacific Ocean. The water carries loosened rock fragments
from the west side of the Sierra Nevada, down toward the
Central Valley, and eventually to the Pacific coast.

Figure 8 As moving water
slows down, its sediment is
deposited in sandbars and
on the beaches.

Beaches
Sand-sized grains of rock loosened from mountains toward
the east provide material for beaches along the Pacific coast.
Beaches are temporary features that must have sediment
added constantly in order to exist. This is because sand is
constantly washed away by ocean currents moving parallel
to the shore. Without rivers continuously adding more sand,
beaches would disappear. Material that has been transported
by a creek and deposited along the Pacific shore is shown in
Figure 8.
Lesson 1 • Landforms

83


Changing Landforms
Although they might seem like permanent features, landforms in your surroundings change continuously. Heat energy
from the Sun and from Earth’s interior provides the energy to
change these landscapes. The constant movement of energy
from Earth’s interior to the surface results in forces that uplift
the land into mountains and plateaus. At the same time, thermal energy from the Sun provides the energy for weather that
includes precipitation, which wears down the uplifted landforms. At times, these changes are abrupt and dramatic, as
when volcanoes erupt. Most often though, the changes are
slow and steady, but endlessly sculpt Earth’s landforms.

LESSON 1 Review
Standards Check

Summarize
Create your own lesson
summary as you design a
visual aid.
1. Write the lesson title,
number, and page numbers at the top of your
poster.
2. Scan the lesson to find
the red main headings.
Organize these headings
on your poster, leaving
space between each.
3. Design an information

box beneath each red
heading. In the box, list
2–3 details, key terms,
and definitions from each
blue subheading.

Using Vocabulary
1. A glacier scraping sediment
and rock from the sides of a
mountain is an example of
2.a
.

5. Compare and contrast the
ways that internal and external forces produce surface
1.f
landforms.

2. In your own words, write a
1.e
definition for landform.

6. Compare and contrast the
formation of Lassen Peak with
the formation of the Sierra
1.e
Nevada.

Understanding Main Ideas

Applying Science
7. Predict what would happen
to Earth’s surface if all of
Earth’s internal heat
1.e
escaped.

3. How did the landform shown
1.e
above most likely form?
A. when a block of rock
uplifted
B. when sediment was piled
up by a river
C. when a volcano erupted
D. when a glacier passed over
a valley

4. Illustrate your poster with
diagrams of important
structures or processes
next to each information
box.

ELA6: R 2.4

4. Identify a landform you have
seen that was made by
2.a
erosion.

84 Chapter 2 • Earth’s Structure

8. Decide if a constantly changing landscape is beneficial for
1.e
people.
Landscape

Benefit

Science

Harm

nline

For more practice, visit Standards
Check at ca6.msscience.com .


How do mountains vary
in shape?
Many different types of landforms make up California’s landscape. Mountains
are especially prominent throughout the state. Explore how to determine the
differences among them and if these differences are clues to how the
mountains formed.

Data Collection
1. Visit ca6.msscience.com to examine some bird’s-eye view images to find
different types of mountains in different regions of California.

2. Make a table of observations like the sample data table below. Use the
menu along the margin of the Web site to observe the mountains listed in
the data table. Explain any differences you observe. Draw some outstanding features for later comparisons.
Mountain Characteristics
Mountain

Colors

Shapes

Unique
Features

Sketch

General
Location

Mt. Shasta
Mt. Eddy
Mt. Diablo
Mt. Whitney

Data Analysis
1. Identify a mountain range that was formed by volcanic eruptions.
2. Compare and contrast characteristics of the mountains you studied.
3. Graph Make a bar graph that includes the names of the mountains and
plateaus and their elevations. Use the following data: Mt. Shasta (4,317 m),
Mt. Eddy (2,751 m), Mt. Diablo (1,173 m), Mt. Whitney (4,417 m).

Science Content Standards
7.c Construct appropriate graphs from data and develop qualitative statements about the relationships between
variables.

85


LESSON 2
Science Content
Standards
2.c Students know beaches are dynamic
systems in which the sand is supplied by
rivers and moved along the coast by the
action of waves.
6.b Students know different natural
energy and material resources, including air,
soil, rocks, minerals, petroleum, fresh water,
wildlife, and forests, and know how to
classify them as renewable or nonrenewable.
6.c Students know the natural origin of
the materials used to make common objects.
7.e Recognize whether evidence is
consistent with a proposed explanation.

Reading Guide
What You’ll Learn
▼

Identify minerals by

observing their properties.

▼

Explain the value of
minerals in your life.

▼

Classify rocks according to
how they form.

▼

Illustrate how the rock
cycle continuously recycles
Earth materials.

Why It’s Important
The majority of Earth
materials, even those in the
deep interior, are solid rock.

Vocabulary
mineral
density
rock
magma

lava

sediment
rock cycle

Review Vocabulary
igneous rock: rock that
forms from magma or lava
(Grade 4)

86

Chapter 2 • Earth’s Structure

Aaron Haupt

Minerals and Rocks
>ˆ˜Ê`i> The solid Earth is made of minerals and rocks.
Real-World Reading Connection You stand on the bank
of a creek and throw rocks in the water. Rocks seem to be
everywhere. But in your yard there are hardly any rocks.
What are rocks? What are they made from? Where do they
come from?
>ˆ˜
`i>

ˆ}
*ˆVÌÕÀi

What is Earth made of ?
,i>`ˆ˜}
The

solid part of Earth is made up of minerals and

…iVŽ
rocks. People use them to build homes and roads. Minerals
and rocks break down to form the soil in which farmers
grow food. Some rocks and minerals are even used as jewelry because they are so beautiful. Minerals and rocks are
such a common part of the environment that you might
not realize they are all around you. Figure 9 shows some
common items made from mineral and rock resources.
Minerals are the substances that make up rocks. Scientists have identified about 3,800 distinct minerals, but most
of these are rare. There are only about 30 common minerals. Minerals form when crystals grow in nature. For example, they can grow in melted rock material or from material
dissolved in water.

Figure 9 Identify items in this picture that you
think were made from minerals or rocks.


What is a mineral?

WORD ORIGIN

The word mineral has several common meanings. You
might drink mineral water, or someone might tell you to eat
healthful food, so that you get all the vitamins and minerals
that you need to be healthy. In Earth science, the word mineral has a specific definition. A mineral is a naturally occurring, generally inorganic solid that has a crystal structure and
a definite chemical composition. How can you tell if something you are looking at is a mineral? Materials classified as
minerals have the following properties.

mineral
minera- Latin; means mine or

ore
mineralis- Latin; means of or
from the mine

Naturally Occurring To be considered a mineral, a substance must be found in the natural world. Anything manufactured by people, such as one of the gemstones in Figure 10,
are not minerals. For example, diamonds mined from Earth
are minerals, but synthetic diamonds made in laboratories
are not.
Generally Inorganic Most minerals are formed by processes
that do not involve living things. But, there are some minerals made by living things. The mineral aragonite is found in
pearls, which are made by oysters, and the mineral apatite is
found in your bones and teeth.
Solid Substances that are liquids or gases are not considered
minerals. Therefore, natural emeralds like the ones shown in
Figure 10 are minerals, but the liquid that would form if they
were to melt is not a mineral.

Figure 10

Natural emeralds are varieties
of the mineral called beryl.

Compare and contrast the appearances of the
synthetic and the natural emeralds.

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Lesson 2 • Minerals and Rocks

87

(l)Geolite/www.geolite.com, (r)Roberto de Gugliemo/Photo Researchers


Crystal Structure The atoms in a mineral are arranged in
orderly, repeating patterns. This regular atomic pattern is
called a crystal structure. The smooth flat surfaces on a crystal represent a well-organized, internal structure of atoms.
Observe the crystal structure of the mineral halite shown in
Figure 11. Notice that the outer, smooth faces of the halite
crystal make the same shape as its internal atomic structure.
Definite Composition A mineral is made of specific elements. Not only must a mineral have certain elements, but
the elements also must be in definite proportions. A common
example is the mineral quartz. It is made of the elements silicon (Si) and oxygen (O). The chemical formula for quartz is
SiO2. The formula tells you there are two oxygen atoms for
every silicon atom in quartz. The chemical formula shows
both the elements and their proportions.

Figure 11

The cubic
nature of the halite crystal
is one property used to
identify it.

Interactive Table Organize information
about minerals at ca6.msscience.com.

Table 1 Is it a mineral?

Amber

Rock Candy

Synthetic
Ruby

Fluorite

Did it form in
nature?

Yes

No

No

Yes

Is it inorganic?

No

No

Yes

Yes

Does it have a
crystal structure?

No

Yes

Yes

Yes

Does it have a
definite chemical
composition?

No

Yes

Yes

Yes

Is it a mineral?

No

No

No

Yes

organic compound
made by humans

made in
laboratories, hard
to distinguish
from natural
rubies

gemstone ranging
in color from clear
or green to violet
and blue black

Comments

common
gemstone; made
of tree resin;
mixture of many
organic
compounds

88 Chapter 2 • Earth’s Structure
(t br)Charles D. Winters/Photo Researchers, (bl)Francois Gohier/Photo Researchers, (bcl)David Young-Wolff/PhotoEdit, (bcr)Chatham Tom Chatham/Created Gems


(l)Paul Silverman/Fundamental Photographs, (r)Dane A. Penland/Smithsonian Institute

Physical Properties
of Minerals
You can tell one mineral from another by
its physical properties. Physical properties are
characteristices that can be observed or measured without changing the identity of the
mineral. If you learn how to test a mineral for
these properties, you will be able to use the
tests to identify many minerals. Some of the
more common physical properties you can
use to identify minerals are described next.

Table 2 Mohs Hardness Scale

Mineral

Hardness

Common
Tests

Talc

1

rubs off
on clothing

Gypsum

2

scratched by
fingernail

Calcite

3

barely
scratched by
copper coin

Fluorite

4

scratches

copper coin
deeply

Apatite

5

about same
hardness as
glass

Feldspar

6

scratches
glass

Quartz

7

scratches
glass and
feldspar

Topaz

8

scratches
quartz

scratched by feldspar?

Corundum

9

scratches
most
minerals

A mineral’s color can sometimes help you
identify it. The mineral malachite, for example, always has a distinctive green color
because it contains the metal copper. Most
minerals do not have a single distinctive
color, as shown by the many colors of quartz
in Figure 12.

Diamond

10

scratches all
common
materials

Hardness
You can test the hardness of a mineral by

observing how easily it is scratched. Any
mineral can be scratched by another mineral
that is harder. In the early 1800s, Austrian
scientist Friedrich Mohs developed a hardness scale with 10 minerals. On this scale, the
hardest mineral, diamond, has a hardness of
10. The softest mineral, talc, has a hardness
of 1. Table 2 shows the Mohs’ hardness scale.
Quartz, feldspar, and calcite are on the scale,
and they all are common minerals.
Table 2 Which minerals can be

Color

Figure 12
Quartz cannot
be identified
by color alone.

Uncut Quartz

Cut Quartz


Figure 13

Constant Streak Although the colors
of hematite can be different, the streak is always
reddish-brown.

Infer which is harder—the porcelain tile or the hematite.

Streak and Luster

Metallic Luster

Streak is the color of powder from a mineral. You can look
at the powder by scratching the mineral across a tile made of
unglazed porcelain. Some minerals that vary in color have
distinct streak colors. For example, the color of the mineral
hematite can be silver, black, brown, or red. But, notice in
Figure 13 that the two different-colored hematite samples
both show a reddish-brown streak.
Luster is the way a mineral’s surface reflects light. Geologists use several common words to describe mineral luster.
Two of these are shown in Figure 14. Galena has a shiny
metallic luster. Quartz has a glassy luster. Other terms used
to describe luster are greasy, silky, and earthy. Look again at
Figure 13 and try to use these terms to describe the luster
of the hematite samples. Do both hematite samples have the
same luster?

Crystal Shape
Glassy Luster
Figure 14 Galena and
quartz have distinctive
crystal shapes and lusters.

Every mineral has a unique crystal shape. A crystal that
forms on Earth’s surface will be small, because the erupting
lava flow cools rapidly. Crystals are large and perfect when
they form underground where Earth’s heat is maintained and

the magma source cools slowly. As Figure 14 illustrates, each
crystal has a distinct shape, which sometimes is referred to
as crystal habit.

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Figure 15

The way a mineral breaks
into pieces can help with identification. Striking a piece of calcite with a
hammer causes it to break along flat
cleavage planes. Quartz mineral (inset)
breaks on curved fracture surfaces.

Quartz

Calcite

Cleavage and Fracture
Cleavage and fracture describe the way a mineral breaks. If
it breaks along smooth, flat surfaces, it has cleavage. A mineral can have one or more distinct cleavage directions. If a
mineral breaks along rough or irregular surfaces, it displays
fracture. Figure 15 shows examples of both cleavage and fracture. The calcite has three distinct cleavage directions. This
makes it break into blocks. Quartz does not have cleavage. It
breaks along curved surfaces, so it displays fracture.
How many directions of cleavage does calcite have?

Density
Density is the amount of matter an object has per unit of
volume. Some minerals are denser than others. If you pick up
a piece of galena and a piece of quartz, and both are about
the same size, you can feel that the galena is much heavier.
This is because galena is denser than quartz.
Most metals have high densities compared to nonmetals.
Minerals with atoms packed closely together also tend to
have higher densities. Quartz and feldspar are common minerals with relatively low densities. Olivine, with a closely
packed structure of atoms and some iron in its structure, has
a relatively high density. When a mineral has an especially
high or low density, its density can be used to identify it.
Lesson 2 • Minerals and Rocks

91


Magnetism

Double Refraction

Figure 16 Both magnetite and calcite have noticeable physical
properties that help identify them.
Explain how the property of magnetism could help physically separate minerals.

Other Properties
Some minerals have properties that make them easy to
identify. For example, magnetite is magnetic. Figure 16 shows
how magnetite attracts a magnet. Calcite reacts chemically to

acids. If you place a drop of acid on calcite, it fizzes.
Calcite also shows an interesting property that occurs when
light interacts with it. If you look at an object through a clear
calcite crystal, you can see two images of the object, as shown
in Figure 16. This is called double refraction, and it occurs
when light splits into two separate rays, each forming its own
distinct image of the object.
What property of calcite produces double images of
objects viewed through it?

Many properties of minerals make them ideal to use in
industry. For example, quartz can produce an electric current
when pressure is applied to it. Graphite can be used to mark
on paper. Copper is used in electronic wiring because it is a
good conductor of electricity.
Every mineral has properties that can be observed to help
identify it. But remember that many minerals have similar
properties. You need to test for a combination of properties to
find those that are unique to a particular mineral. It can be a
challenge to find an unfamiliar mineral and try to figure out
what it is.
92 Chapter 2 • Earth’s Structure
(l)Breck P. Kent, (r)Tim Courlas


Mineral Identification
by Property
It can be challenging to identify a mineral correctly, because many of them have similar properties. But, with a few simple tools, you can observe a set of characteristic
physical properties for an unknown mineral. This can help you determine what it is.

Procedure
1. Complete a safety worksheet.
2. Obtain three or four unknown numbered mineral samples from your teacher.
3. Use a field guide for rocks and minerals, a magnifying glass, a streak plate, a
copper coin, a glass plate, a magnet, a graduated cylinder, and a triple-beam balance to help you determine the physical properties of each sample.

4. For each sample, observe and record the physical properties, color, streak, luster,
hardness, and cleavage or fracture using information in Lesson 2.

5. To determine the density of a sample, place it on the triple-beam balance and measure the mass in grams. Then tie a string around the sample and carefully lower it
into the graduated cylinder that has a recorded volume of water in it. Subtract the
original volume from the new volume of water. Divide the mass by the volume.
Properties to Identify Minerals
Mineral
Name

Color

Streak

Luster

Hardness

Cleavage/
Fracture

Density
(g/mL)

Other
Properties

Analysis
1. Compare your results to the information in the field guide.
2. Identify each mineral using your observations and the guide.
3. Evaluate which properties were most helpful for you to identify a mineral.
Describe any properties that could help you identify a mineral without testing
other properties.

Science Content Standards
7.e Recognize whether evidence is consistent with proposed explanation.

93


Mineral Uses
Some minerals are important because they contain materials that have many uses. Others are important because they
have special properties or because they are rare. People
appreciate some minerals solely for their beauty.

ACADEMIC VOCABULARY
appreciate (uh PRE
shee ayt)

Metallic Ores

(verb) to grasp the nature,
quality, worth or significance
of

It is difficult for most people to
appreciate patience.

Rich deposits of valuable minerals are called ores. The metals you use every day come from these ores. The minerals
chalcopyrite and malachite are examples of copper ores. Copper is a common metal used in wires to conduct electricity.
Iron used to make steel comes from hematite and magnetite. Steel is used to manufacture cars, bridges, skyscrapers,
and many other things you use every day. Galena is the major
ore for producing lead. Most lead is used to manufacture automobile batteries. The minerals gold and silver are considered
precious metals. They are used in industry and also in jewelry.
What is the major ore used for producing lead?

Gemstones
People have been collecting minerals for their beauty for
thousands of years. These minerals are called gems. Many
gems have intense colors, a glassy luster, and are 7 or more on
the Mohs hardness scale. Diamonds, rubies, sapphires, and
emeralds are among the most valuable gemstones. When
these rare minerals are cut and polished, their value can last
for hundreds of years. Figure 17 shows the difference between
these minerals before and after they are cut and polished.

Figure 17

The clear
diamond, ruby, blue
sapphire, and ruby
are cut and polished
to make jewelry.

Uncut

diamond
Uncut sapphire

Cut ruby on uncut matrix

Cut sapphire

Cut diamond

94 Chapter 2 • Earth’s Structure
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Rocks
A rock is a natural, solid mixture of particles. These particles are made mainly of individual mineral crystals, broken
bits of minerals, or rock fragments. Sometimes rocks contain
the remains of organisms or are made of volcanic glass. Geologists call the particles that make up a rock grains.
Most of Earth is made of rocks. Mountains, valleys, and
even the seafloor under the oceans are made of rocks. You
might not always notice the rocks under your feet. Figure 18
shows an example of how rocks and soil are present beneath
a landscape’s surface.
Rocks are classified, or placed into groups, based on
the way they form. There are three major groups of rocks:
igneous rocks, metamorphic rocks, and sedimentary rocks.
Figure 18 What happens to particles eroded from the
mountains?

Figure 18

After breaking, pieces
of the crust move up or down
along the faults, producing
mountains, hills, and valleys.

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Lesson 2 • Minerals and Rocks

95


Igneous Rocks
Igneous rocks are formed from molten, or liquid, rock
material called magma. As the temperature of magma drops,
tiny crystals of minerals begin to form. These tiny crystals
become the grains in an igneous rock.
Located at Earth’s surface, magma, now called lava, cools
quickly. The crystals in lava do not have much time to grow,
so they are small. Volcanic glass forms when lava cools so rapidly that atoms do not form well-organized crystal structures.
Deep within Earth, magma cools slowly because thick layers of rock surround it. There is more time for larger crystals
to grow. Figure 19 shows a cross-section, or slice, through
Earth. Notice that the igneous rock called granite in
Figure 19 has larger mineral grains than the igneous rock
called basalt. This is because granite cools much more slowly
than basalt does.
Why does magma cool slowly?

Figure 19 Cooling Rates The grain
size of an igneous
rock depends in part
on how quickly the
magma cools.

Like the word mineral, texture is a common word. But in
Earth science it has a specific definition. The grain size and
the way grains fit together in a rock are called texture.
Because granite and basalt have different-sized grains, they
have different textures. Granite’s texture is coarse grained

and basalt’s texture is fine grained. Figure 20 shows El Capitan, which is a huge mountain of granite now exposed at the
surface by uplift.
The igneous rocks granite and basalt do not differ only in
texture. They also differ in mineral composition. Granite
contains low-density minerals such as quartz and feldspar.
Basalt is made of higher-density minerals than granite, such
as olivine and magnetite.
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96 Chapter 2 • Earth’s Structure
(l)George Bernard/Photo Researchers, (r)Carolina Biological Supply Company/PhotoTake NYC


Visualizing Igneous Rock Features
▲

Figure 20
Intrusive igneous rocks are formed when a mass of
magma is forced upward toward Earth’s surface and
then cools before emerging. The magma cools in a

variety of ways. Eventually the rocks may be uplifted
and erosion may expose them at Earth’s surface. A
selection of these formations is shown here.

This dike in Israel’s
Negev Desert formed
when magma squeezed
into cracks that cut
across rock layers.

▲

A batholith is a large
igneous rock body that
forms when rising
magma cools below
the ground. Towering
El Capitan, right, is just
one part of a huge
batholith. It looms over
the entrance to the
Yosemite Valley.

▲ Sills such as this
one in Death Valley,
California, form when
magma is forced into
spaces that run parallel to rock layers.

▲

Volcanic necks like Shiprock, New Mexico, form when
magma hardens inside the vent of a volcano. Because the
volcanic rock in the neck is harder than the volcanic rock in
the volcano’s cone, only the volcanic neck remains after erosion wears the cone away.
Contributed by National Geographic

Lesson 2 • Minerals and Rocks

97

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Metamorphic Rocks

SCIENCE USE V. COMMON USE
grain
Science Use a small, hard particle or crystal A grain of sand
looks much like any other.
Common Use seed or fruit of
cereal grass Rice is eaten by
more people than any other
cereal grain.

Metamorphic rocks form when solid rocks are squeezed,
heated, or exposed to fluids, changing them into new rocks.
To be considered metamorphic, rocks must stay solid as they
change. If the conditions are correct to melt them, new igneous rocks will form instead of metamorphic rocks.
The original rock that is changed is called the parent rock.

Heat, pressure, and hot fluids composed mainly of water and
carbon dioxide applied to a parent rock cause the growth of
new mineral grains. These new grains may have a different
texture and might even have a different mineral composition
than the grains in the parent rock.
When exposed to heat, pressure, or fluids, what can
happen to mineral grains?

Figure 21 shows changes that can happen when two parent
rocks are metamorphosed. Increased pressure and temperature made the grains in the marble bigger and sparkly, compared to the grains in the parent limestone. The grains remain
as crystals of calcite, but they are larger than in limestone.
The metamorphic rock, gneiss (NISE), in Figure 21 shows a
more dramatic texture change. Look closely at the parallel
layers of dark and light mineral grains. This layering is called
foliation. Foliation results from uneven pressure.

Figure 21
Metamorphism can change a rock’s texture or
composition.

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Chapter 2 • Earth’s Structure

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