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

Rocks

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

Rocks

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

Rocks

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

Rocks

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

- Classifying Rocks

Rocks

Rocks

Sedimentary

includeinclude include

can be

IntrusiveNon-

foliatedClastic

Graphic Organizer

Igneous Metamorphic

Extrusive Organic Chemical Foliated

Rocks

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

Rocks

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

- 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

Rocks

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

Rocks

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

Rocks

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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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