Rocks

Classifying Rocks

Igneous Rocks

Sedimentary Rocks

Rocks from Reefs

Metamorphic Rocks

The Rock Cycle

Table of Contents

Rocks

Classifying Rocks

Rocks

How Geologists Classify RocksWhen studying a rock sample, geologists observe three things:

1) Origin

2) texture

3) mineral composition.

Rocks

Texture• Texture is the look and feel of the rock’s surface.

• Texture can be smooth, glassy, rough or chalky.

• http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page06.cfm?chapter_no=investigation

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Grains• Particles of minerals or other rocks that make up a rock

• Grains are large and easy to see = coarse-grained

• Grains so small they can only be seen with microscope

= fine-grained

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Grain Shape• Grain shapes can be round or jagged

• Also result from crystal shape

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Grain Pattern• Can be dotted throughout (non-banded)

• Can be organized in horizontal rows (banded)

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No Visible Grain• No grain visible even under microscope

• This occurs when lava cools very quickly

• Extremely small pieces of silica make up the rock

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Mineral CompositionUsing a microscope to identify minerals by cutting a thin slice

Use acid to detect carbon (Calcium Carbonate)

Also test with magnet to detect iron or nickel (magnetic properties

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How Rocks FormGeologists classify rocks into three major groups: igneous rock, sedimentary rock, and metamorphic rock.

- Classifying Rocks

Rocks

Asking QuestionsBefore you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.

What does a rock’s color tell you?

It can provide clues about the rock’s mineral and chemical composition.

How do geologists describe a rock’s texture?

Geologists use terms based on the size, shape, and patterns of the grains.

Question Answer

- Classifying Rocks

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Igneous Rock

Forms when molten rock (magma/lava) cools and hardensCools slowly beneath Earth’s surface = intrusiveCools rapidly on the surface = extrusiveIntrusive rocks usually have large, visible grainsExtrusive rocks usually have small to no visible grainsColor is based on the amount of silica in the magma

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Sedimentary Rocks

Forms from the compaction and cementation of rock pieces, mineral grains, or organic matter called sedimentsCan contain fossilsSediments are formed through the process of weathering and erosion of exposed rocks.

Rocks3 kinds:

Clastic = made of mineral or rock pieces (shale; conglomerate; sandstone; Breccia)Organic = made from plant or animal remains (coal; coquina; some limestones)Chemical = made from dissolved minerals in water (halite; other limestones)

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Metamorphic RockForms when rocks are changed into different kinds of rocks by great heat and pressureThey are heated, squeezed, folded, or changed by contact with hot magma.2 kinds:

foliated = grains are in bandsnonfoliated = no banding

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End of Section:Classifying

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Classifying Igneous RocksIgneous rocks are classified according to their origin, texture, and mineral composition.

- Igneous Rocks

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Mineral Mixture

Granite is a mixture of light-colored minerals, such as feldspar and quartz, and dark-colored minerals, including hornblende and different types of mica. But granite can vary in mineral composition. This affects its color and texture.Study the circle graph and then answer the questions.

- Igneous Rocks

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Mineral Mixture

Feldspar

Reading Graphs:

What mineral is most abundant in granite?

- Igneous Rocks

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Mineral Mixture

10%

Reading Graphs:

About what percentage of granite is made up of dark minerals?

- Igneous Rocks

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Mineral Mixture

100% - (35% + 10%) = 55%

Calculating:

If the amount of quartz increases to 35 percent and the amount of dark-colored minerals stays the same, what percentage of the granite will be made up of feldspar?

- Igneous Rocks

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Mineral Mixture

The overall color would be darker.

Predicting:

How would the color of the granite change if it contained less feldspar and more mica and hornblende?

- Igneous Rocks

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Detail Detail Detail

Main Idea

As you read the section “Classifying Igneous Rocks,” write the main idea in a graphic organizer like the one below. Then write three supporting details. The supporting details further explain the main idea.

Igneous rocks are classified by origin, texture, and composition.

Extrusive rock forms from lava on the surface; intrusive rock forms from magma from beneath the surface.

Intrusive rocks have larger crystals than extrusive rocks because they cool more slowly.

High-silica rocks are light colored; low-silica rocks are dark colored.

- Igneous Rocks

Identifying Main Ideas

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Links on Igneous Rocks

Click the SciLinks button for links on igneous rocks.

- Igneous Rocks

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End of Section:Igneous Rocks

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From Sediment to RockMost sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.

- Sedimentary Rocks

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OutliningAs you read, make an outline about sedimentary rocks. Use the red headings for the main topics and the blue headings for the subtopics.

Sedimentary RocksI. From Sediment to Rock

A. ErosionB. DepositionC. CompactionD. Cementation

II. Types of Sedimentary RockA. Clastic RocksB. Organic RocksC. Chemical Rocks

III. Uses of Sedimentary RocksA. Building MaterialsB. Tools

- Sedimentary Rocks

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Links on Sedimentary Rocks

Click the SciLinks button for links on sedimentary rocks.

- Sedimentary Rocks

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End of Section:Sedimentary

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What You Know

What You Learned

Using Prior KnowledgeBefore you read, look at the section headings and visuals to see what this section is about. Then write what you know about coral reefs in a graphic organizer like the one below. As you read, write what you learn.

1. Coral reefs grow in the oceans.2. Florida has coral reefs.3. Oceans used to be where there is dry land now.

1. Coral animals cannot live below 40 meters.2. In the United States, only the coasts of Florida and Hawaii have coral

reefs.3. Some limestone deposits on land formed from ancient reefs.

- Rocks From Reefs

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More on Coral Landforms

Click the PHSchool.com button for an activityabout coral landforms.

- Rocks From Reefs

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End of Section:Rocks From

Reefs

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Previewing VisualsBefore you read, preview Figure 17. Then write two questions that you have about metamorphic rocks in a graphic organizer like the one below. As you read, answer your questions.

Previewing

Q. Why do the crystals in gneiss line up in bands?

A. Gneiss is a type of metamorphic rock that is foliated—the crystals are flattened to form parallel lines.

Q. How does quartzite form from sandstone?

A. High temperature and pressure on the minerals in sandstone cause them to be changed into minerals that make up quartzite.

- Metamorphic Rocks

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Links on Metamorphic Rocks

Click the SciLinks button for links on metamorphic rocks.

- Metamorphic Rocks

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End of Section:Metamorphic

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A Cycle of Many PathwaysForces deep inside Earth and at the surface produce a slow cycle that builds, destroys, and changes the rocks in the crust.

- The Rock Cycle

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Rock Cycle Activity

Click the Active Art button to open a browser window and access Active Art about the rock cycle.

- The Rock Cycle

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Magma

Rock Cycle

SequencingAs you read, make a cycle diagram that shows stages in the rock cycle. Write each stage of the rock cycle in a separate circle in your diagram.

Igneous

Sedimentary

Metamorphic

- The Rock Cycle

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End of Section:The Rock Cycle

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Sedimentary

includeinclude include

can be

IntrusiveNon-

foliatedClastic

Graphic Organizer

Igneous Metamorphic

Extrusive Organic Chemical Foliated

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End of Section:Graphic Organizer