Table of Contents Classifying Rocks Igneous Rocks Sedimentary Rocks Rocks from Reefs Metamorphic Rocks The Rock Cycle

Classifying Rocks

How Geologists Classify Rocks When studying a rock sample, geologists observe three things: Origin texture mineral composition.

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

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

Grain Shape Grain shapes can be round or jagged Also result from crystal shape

Grain Pattern Can be dotted throughout (non-banded) Can be organized in horizontal rows (banded)

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

Mineral Composition Using 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

How Rocks Form - Classifying Rocks Geologists classify rocks into three major groups: igneous rock, sedimentary rock, and metamorphic rock.

Asking Questions - Classifying Rocks Before 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. Question Answer 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.

Igneous Rock Forms when molten rock (magma/lava) cools and hardens Cools slowly beneath Earth’s surface = intrusive Cools rapidly on the surface = extrusive Intrusive rocks usually have large, visible grains Extrusive rocks usually have small to no visible grains Color is based on the amount of silica in the magma

Sedimentary Rocks Forms from the compaction and cementation of rock pieces, mineral grains, or organic matter called sediments Can contain fossils Sediments are formed through the process of weathering and erosion of exposed rocks.

3 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)

Metamorphic Rock Forms when rocks are changed into different kinds of rocks by great heat and pressure They are heated, squeezed, folded, or changed by contact with hot magma. 2 kinds: foliated = grains are in bands nonfoliated = no banding

End of Section: Classifying Rocks

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

Mineral Mixture - Igneous Rocks 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.

Mineral Mixture - Igneous Rocks Reading Graphs: What mineral is most abundant in granite? Feldspar

Mineral Mixture - Igneous Rocks Reading Graphs: About what percentage of granite is made up of dark minerals? 10%

Mineral Mixture - Igneous Rocks 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? 100% - (35% + 10%) = 55%

Mineral Mixture - Igneous Rocks Predicting: How would the color of the granite change if it contained less feldspar and more mica and hornblende? The overall color would be darker.

Identifying Main Ideas - Igneous Rocks Identifying Main Ideas 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. Main Idea Igneous rocks are classified by origin, texture, and composition. Detail Detail Detail 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.

Click the SciLinks button for links on igneous rocks.

End of Section: Igneous Rocks

From Sediment to Rock - Sedimentary Rocks Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.

Outlining - Sedimentary Rocks As you read, make an outline about sedimentary rocks. Use the red headings for the main topics and the blue headings for the subtopics. From Sediment to Rock Erosion Deposition Compaction Cementation Types of Sedimentary Rock Clastic Rocks Organic Rocks Chemical Rocks Uses of Sedimentary Rocks Building Materials Tools

Links on Sedimentary Rocks Click the SciLinks button for links on sedimentary rocks.

End of Section: Sedimentary Rocks

Using Prior Knowledge - Rocks From Reefs Before 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. What You Know Coral reefs grow in the oceans. Florida has coral reefs. Oceans used to be where there is dry land now. What You Learned Coral animals cannot live below 40 meters. In the United States, only the coasts of Florida and Hawaii have coral reefs. Some limestone deposits on land formed from ancient reefs.

More on Coral Landforms - Rocks From Reefs More on Coral Landforms Click the PHSchool.com button for an activity about coral landforms.

End of Section: Rocks From Reefs

Previewing Visuals - Metamorphic Rocks Before 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.

Links on Metamorphic Rocks Click the SciLinks button for links on metamorphic rocks.

End of Section: Metamorphic Rocks

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

Rock Cycle Activity - The Rock Cycle Click the Active Art button to open a browser window and access Active Art about the rock cycle.

Sequencing - The Rock Cycle As 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. Metamorphic Igneous Sedimentary

End of Section: The Rock Cycle

Graphic Organizer Igneous Metamorphic Extrusive Organic Chemical Foliated

End of Section: Graphic Organizer