2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 3 Minerals and Rocks Objectives Identify the three types of rock. Explain the properties of each type of rock based on physical and chemical conditions under which the rock formed. Describe the rock cycle and how rocks change form. Explain how the relative and absolute ages of rocks are determined. Chapter 21

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer In this section you will be studying rocks and minerals. Rocks are identified by the minerals they contain, the size of their crystals, and other properties. Using the following flowchart, list the properties of the rocks named below. 1.Rock is light colored. go to 2 Rock is dark colored. go to 4 2.Rock has large crystals. Granite Rock has small crystals. go to 3 3.Rock is very light and fine grained with a streak of color. Marble Rock is fine grained with definite layers. sandstone 4.Rock has definite small crystals. Basalt Rock has no obvious crystal structure. go to 5 5.Rock is hard, dark, and glasslike. Obsidian Rock is porous, has air bubbles, and crumbles when rubbed over a hard surface. pumice Section 3 Minerals and Rocks Chapter 21

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer, continued Using the flowchart on the previous slide, list the properties of the rocks named below. Granite Basalt Obsidian Sandstone Section 3 Minerals and Rocks Chapter 21

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks All rocks are composed of minerals. There are about 3500 known minerals in Earth’s crust. Each combination of rock-forming minerals results in a rock with a unique set of properties. Mineral a natural, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties Section 3 Minerals and Rocks Chapter 21

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks, continued Molten rock cools to form igneous rock. Nearly all igneous rocks are made of crystals of various minerals. Igneous rock rock that forms with magma cools and solidifies Extrusive igneous rock cools on Earths surface Intrusive igneous rock cools while trapped beneath Earth’s surface Section 3 Minerals and Rocks Chapter 21

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Comparing Intrusive and Extrusive Igneous Rock Section 3 Minerals and Rocks Chapter 21

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks, continued Remains of older rocks and organisms form sedimentary rocks. All rock breaks down over thousands of years. Weathering the natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes, disintegrate and decompose rocks Section 3 Minerals and Rocks Chapter 21

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks, continued As pieces of rock accumulate, they can form another type of rock. Sedimentary rock a rock formed from compressed or cemented layers of sediment Sediment accumulated pieces of rock and other particles Section 3 Minerals and Rocks Chapter 21

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks, continued Loose sediment forms rock in two ways. 1.Layers of sediment get compressed from weight above, forming rock. 2.Minerals dissolved in water seep between bits of sediment and “glue” them together. Sedimentary rocks are named according to the size of the fragments they contain. Section 3 Minerals and Rocks Chapter 21

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks, continued Rocks that undergo pressure and heating without melting form metamorphic rock. Heat and pressure within Earth cause changes in the texture and mineral content of rocks. Metamorphic rock a rock that forms from other rocks as a result of intense heat, pressure, or chemical processes Section 3 Minerals and Rocks Chapter 21

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Types of Rock Section 3 Minerals and Rocks Chapter 21

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure and Origin of Rocks, continued Old rocks in the rock cycle form new rocks. The sequence of events in which rocks can be weathered, melted, altered, and formed is described by the rock cycle. Rock formation occurs very slowly, often over tens of thousands to millions of years. Section 3 Minerals and Rocks Chapter 21

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Rock Cycle Section 3 Minerals and Rocks Chapter 21

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How Old Are Rocks? The relative age of rocks can be determined using the principle of superposition. The principle of superposition states the following: Assuming no disturbance in the position of the rock layers, the oldes will be on the bottom, and the youngest will be on top. Section 3 Minerals and Rocks Chapter 21

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Superposition Section 3 Minerals and Rocks Chapter 21

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How Old Are Rocks? continued Radioactive dating can determine a more exact, or absolute, age of rocks. The radioactive elements that make up minerals in rocks decay over billions of years. Physicists have determined the rate at which these elements decay. Geologists can use this data to determine the age of rocks. Section 3 Minerals and Rocks Chapter 21

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Concept Mapping Section 4 Weathering and Erosion Chapter 21