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CHECK Complete the following - Leonard Bernstein • Martin Schachter • Alan Winkler • Stanley Wolfe

CHECK

Complete the following.

1



How are igneous rocks formed?



Objective ► Identify two ways that igneous rocks are formed.

TechTerms

lava

(LAH-vuh): magma that reaches the earth's surface

magma

(MAG-muh): molten rock inside the earth

molten

(MOHL-tun)

rock:

melted minerals

Heat Inside the Earth

The temperature of the earth becomes hotter as you dig deeper into the earth. Two meters beneath the earth's surface, the temperature is about 10 °C. The deepest oil wells have been drilled about 6 km into the earth. Here, the temperature is more than 60 °C. Between the earth's crust and the mantle (MAN-tul), the temp­erature is between 600 and 700 °C. The mantle is the layer of the earth below the crust.

The temperature between the crust and the mantle is high enough to melt minerals. Melted minerals are called

molten

(MOHL-tun) rock. When molten rock cools, igneous rocks form. Igneous rocks are sometimes called "fire-formed" rocks. Although fire does not form igneous rocks, tremendous heat melts rock.

Explain:

How do igneous rocks form?

60° C



Figure 2



Magma and Igneous Rocks

Molten rock inside the earth is called

magma

(MAG-muh). There are large pools of magma deep inside the earth. Sometimes, magma rises through cracks between rocks into the upper part of the earth's crust. Here, the temperature is much cooler than deep inside the earth. As magma rises through cracks in the earth's crust, the magma cools and hardens. Igne­ous rock is formed. Igneous rock can take thou­sands of years to cool from magma.

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Define: What is magma?

Lava and Igneous Rocks

Sometimes magma rises through cracks in rocks and reaches the earth's surface. Magma that reaches the earth's surface is called

Java

(LAH-vuh). Lava cools upon contact with air or water. Cooling makes lava harden into igneous rock. Igneous rocks form from lava in a short period of time.

illljll^ Describe: How does lava rise to the earth's surface?

IGNEOUS ROCK FORMATIONS



Figure 1

Igneous rock formation


LESSON SUMMARY



6.

Explain the difference between the formation of igneous rocks from magma and lava.

InfoSearch

........................................



Read the passage. Ask two questions about the topic that you cannot answer from the information in the passage.



Pllltons

Large bodies of igneous rock with differ­ent shapes are formed when magma cools inside the earth. These bodies of igneous rocks are called batholiths (BATH-uh-liths), stocks, laccoliths (LAK-uh-liths), dikes, and sills. A general name for all of these bodies of igneous rock is pluton (PLOO-tahn). An example of each kind of pluton is shown in Figure 1 on page 62. Plutons form inside the earth. However, in some areas of the United States, you can see plutons at the earth's surface.

SEARCH: Use library references to find answers to your questions.



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JAMES

HUTTON (1726-1797)



James Hutton was born in Edinburgh, Scotland. He was trained to be a doctor. However, after Hutton inherited a farm from his father, he became interested in the natural forces at work on the earth's surface. At the time, scientists thought that all rocks were sedimentary rocks. Hutton had a different idea. He said that many rocks, such as granite, were once molten. Hutton also snowed that mountains could be formed by the upward push of molten, or igneous, rocks. Hutton published his ideas in a book called

Theory of the Earth

in 1795.



As a result of his studies of the earth, Hutton proposed a theory about the history of the earth. Hutton's theory said that the earth was shaped in the past by the same forces that are still at work today. These forces include erosion. Hutton's theory was the beginning of the modern science of geology. Hutton is sometimes called the father of geology.



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► The temperature becomes hotter as you go deeper inside the earth.

► Igneous rocks form from molten rock.

► Magma is molten rock inside the earth.

► Lava is molten rock on the earth's surface.

CHECK

Write true if the statement is true. If the statement is false, change the underlined term to make the statement true.



1

. Igneous rocks formed from magma, form in a short time.

2.

Molten rock that reaches the earth's surface is called magma.

3.

Large pools of magma are found deep inside the earth's crust.

4.

Igneous rock forms from molten minerals.

APPLY

Complete the following.



]|

5. Predict:

If you dug a hole two meters deep into the earth's surface, would you find molten rock? Explain.

7.

When molten rock pours out of a volcano, what is the rock called?

How are igneous rocks classified?



► Identify and describe igneous rocks by their minerals and textures.

> texture

(TEKS-chur): size of the crystals in an igneous rock

A Mixture of Minerals

Igneous rocks are made up of different kinds of minerals. There are six minerals that are commonly seen in igneous rocks. These six minerals are listed in Table 1.



quartz



olivine



feldspar



amphibole



mica



pyroxene



Igneous rocks can be identified by their minerals. Granite (GRAN-it) is an igneous rock made up of quartz, feldspar, and mica. Look at the photograph of granite. You can see each mineral.

Figure 1

Granite



Observe:

Look at the photograph of granite. How do the colors of the quartz and feldspar crystals in granite differ?

Crystal Size

Igneous rocks have crystals of dif­ferent sizes. Crystal size depends upon the amount of time it takes the magma in a rock to cool. Large crystals take a long time to form. Igneous rocks

formed from magma have large mineral crystals. Small crystals take a short time to form. Most igneous rocks formed from lava have very small crystals. Sometimes lava cools so quickly that no crystals form. For this reason, a few igneous rocks do not have any crystals. Obsidian is an igneous rock that does not have any crystals.

Figure 2

Obsidian



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Relate:

How are cooling rate and crystal size related?

Texture

The size of the crystals in an igneous rock is called its

texture

(TEKS-chur). Texture can be used to identify different igneous rocks that are made up of the same minerals. Granite and rhyo-lite (RY-oh-lite) are igneous rocks that are made up of the same minerals. You can tell if a rock is granite or rhyolite by looking at its texture. Gran­ite has large crystals that you can see and feel. Rhyolite has very small crystals that cannot be seen.

Igneous rocks are classified according to their textures. Igneous rocks with large crystals have a coarse texture. Igneous rocks with small crystals have a fine texture. Igneous rocks that do not have crystals have a glassy texture.

&

Classify:

Classify granite, obsidian, and rhy­olite according to their textures.

LESSON SUMMARY



APPLY

Complete the following.



► The minerals in an igneous rock can be used to identify the rock.

► Crystal size is determined by the rate at which magma cools.

► The size of the crystals in an igneous rock is its texture.

► Igneous rocks can be classified according to their textures.

mm

Analyze:

A

rock collector found five igneous rocks. The rocks had mineral crystals with these sizes: Rock A = 2 mm; Rock B = 7 mm; Rock C = 4.5 mm; Rock D = 10 mm; Rock E = .5 mm

6.

Which rocks probably cooled from lava?

7.

Which rocks probably cooled from mag­ma?

8.

Which rock probably took the longest time to cool?

CHECK

Complete the following.



1.

Granite is made up of the minerals feld-

Skill Builder.



spar,

and mica.

Igneous rocks formed from magma usually have_mineral crystals.

An - igneous rock with very small mineral crystals most likelyibrmed from_.

The texture of an igneous rock with no crys­tals is described as__

The texture of rhyolite would be described

as__

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Classifying

When you classify, you group things that are alike in some way. Petrologists often classify igneous rocks according to where the rocks formed. Igneous rocks that formed at the earth's surface are classified as

. extrusive (ihk-STROOS-iv) igneous rocks. Ig­neous rocks that formed inside the earth are classified as intrusive (in-TROO-sive) igneous rocks. Using information in this lesson, classi­fy granite, obsidian, and rhyolite as intrusive or extrusive.

Activity



CLASSIFYING IGNEOUS

ROCKS USING CRYSTAL SIZE

• •••••••••••

You will need a hand lens, samples of diorite, gabbro, and basalt, paper, and a pencil.



1. Copy Table 1 on a clean sheet of paper.



2.

Observe:

Carefully examine each of your rock samples with the hand lens.



3.

Record your observations in your table.

Questions



1.

Which igneous rocks formed deep inside the earth? Explain your answer.



2.

Which rocks formed on the earth's surface? Explain your answer.



Classify:

Using information from this lesson, add granite, obsidian, and

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rhyolite to your table.



Table

1



Classifying Igneous Rocks !



ROCK



CRYSTAL SIZE



TEXTURE



Diorite







Gabbro







Basalt





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How are sedimentary rocks formed?



> Describe two ways that sedimentary rocks are formed.

> sediment

(SED-uh-munt): rock particles that settle in a liquid

Sediments

What happens when you mix mud and sand in a jar of water? The particles of mud and sand settle to the bottom of the jar. The mud and sand settle in layers. The sand settles first because it is heavier than the mud. The mud settles on top of the sand. Mud and sand are examples of

sediments

(SED-uh-munts). Sedi­ments are rock and mineral particles that settle in a liquid.

Sand



lakes, rivers, or oceans. Over millions of years, the sediments pile up in layers. The layers of sediment may be hundreds of meters thick. As more sedi­ment is added to the layers, the lower layers of sediment become tightly packed under the weight of the new layers. The older sediments become solid rock when water and air are squeezed out from between the sediment layers. The sediments also may become rock as dissolved minerals in the water cement the sediments together.

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Describe:

When does sediment become solid rock?

Sedimentary Rock From Living Things

Some sedimentary rocks form from the remains of living things. For example, some sedimentary rocks form from the shells of sea animals. When clams and snails die, their shells are left on the bottom of the ocean. The shells pile up in layers. Minerals in the water cement the shells together. Coquina (koh-KEE-nuh) is a sedimentary rock formed from cemented shells. Shell limestone also forms from shells. However, you cannot see the shells in shell limestone. The shells were smashed into small pieces by ocean waves.

[!!►

Restate:

Define sediment in your own words.

Natural Concrete

Many sedimentary rocks form in much the same way as concrete. Concrete is made up of sand and gravel. Have you ever seen the trucks that pour concrete for a building? Inside these trucks, sand, gravel, cement, and water are mixed. After the mixture is poured out, the water evaporates. When the water evaporates, the sand and gravel become cemented together to form solid concrete.

How do sedimentary rocks form? Most sedi­mentary rocks are formed in water. These rocks form from sediments that settle to the bottoms of

Coquina



Shell limestone



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Identify:

How do the shells of coquina stick together?

LESSON SUMMARY



6.

Why must water evaporate for sedimentary rock to form?

7.

Analyze:

How can shell limestone form from coquina?

8.

Compare:

How are shell limestone and coqui­na alike?

9.

How does weight affect the way in which sediments form layers?

Designing an Experiment

..................



Design an experiment to solve the problem.



PROBLEM: How can you find out the order in which mud, sand, gravel, and pebbles settle in water?

Your experiment should:



1.

List the materials you need.

2.

Identify safety precautions that should be followed.

3.

List a step-by-step procedure.

4.

Describe how you would record your data.

The city of Dover is located along the southeastern coast of England. Dover is known worldwide for its beautiful white cliffs. The cliffs are composed of deposits of natural chalk. These chalk deposits are more than 100 million years old.



How were the "White Cliffs of Dover" formed? The natural chalk comes from the fossil shells of microscopic animals called forams. Microscopic examination of the chalk deposits reveal the shells of the forams that formed them.



The shells of forams are made up of calcium carbonate (CaC0

3

). When the forams die, their shells sink to the ocean bottom. In many parts of the oceans, there is a constant rain of these shells. The shells of the forams form fine sediments on the ocean bottom. Gradually, these sediments build up until they are hundreds of meters thick. Because of their great thickness, the sediments are compressed to form solid rock.


► Sediment are small pieces of rocks and minerals.

► Sedimentary rock forms in much the same way as concrete.

► Sedimentary rock is formed when sediments become cemented together by dissolved minerals.

► Some sedimentary rocks form from the re­mains of living things.

CHECK

Complete the following.



1.

What sedimentary rock is made up of whole shells?

2.

What is sediment?

3.

Name two examples of sediment.

4.

What materials cement the sediments in sedi­mentary rocks together?

APPLY

Complete the following.



W

5. Infer:

Why does sedimentary rock form in layers?

How are sedimentary rocks classified?



► Identify and describe the two main groups of sedimentary rock.

elastics

(KLAS-tiks): sedimentary rocks made up of pieces of rock

nonclastics:

sedimentary rocks made up of dissolved minerals, or the remains of living things

Groups of Sedimentary Rocks

There are two groups of sedimentary rocks. One group is made up of sediments that have been cemented and pressed together. These sedimentary rocks are called

elastics

(KLAS-tiks). Another group of sedi­mentary rock is made up of dissolved minerals, or the remains of plants and animals. These sedi­mentary rocks are

nonclastics.



Illllll^

Define:

What are elastics?

Figure 1

Clastic Sedimentary rocks



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