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Chapter6 Rocks Chapter Outline 1 ● Rocks and the Rock Cycle Three Major Types of Rock The Rock Cycle Properties of Rocks 2 ● Igneous Rock The Formation of Magma Textures of Igneous Rocks Composition of Igneous Rocks Intrusive Igneous Rock Extrusive Igneous Rock 3 ● Sedimentary Rock Formation of Sedimentary Rocks Chemical Sedimentary Rock Organic Sedimentary Rock Clastic Sedimentary Rock Characteristics of Clastic Sediments Sedimentary Rock Features 4 ● Metamorphic Rock Formation of Metamorphic Rocks Why It Matters Classification of The hundreds of different types of Metamorphic Rocks rocks on Earth can be classified into three main types: igneous, sedimentary, and metamorphic. This formation in Arizona is made of sedimentary rock. When you know the type of rock, you know something about how that rock formed. 132 Chapter 6 hq10sena_rxscho.indd 1 3/25/09 4:10:29 PM Inquiry Lab Sedimentary Sandwich 15 min Use slices of different types of bread to model Questions to Get You Started layers of different types of sediment deposits. Next, 1. Make a labeled diagram showing the rock layers in put your model in a plastic bag. Place a weight on the sample you observed. top of the bag to simulate the process of 2. Which factors might affect the thickness of a rock compacting sediment into rock. Then, use an empty layer in a real rock formation? film canister to obtain a core sample of the sedimentary sandwich. Trade samples with another 3. Your model has layers of different types of rocks. group and observe the other group’s sample. In a real formation, what might changes in Identify the different layers of rock and determine if rock type indicate about the rock layers are the same thickness or if some are formation’s geological history? thicker than others. 133 hq10sena_rxscho.indd 2 3/25/09 4:10:53 PM These reading tools will help you learn the material in this chapter. FoldNotes Graphic Organizer Pyramid Pyramid FoldNotes help you Chain-of-Events Chart A chain-of-events compare words or ideas in sets of three. chart is similar to a flow chart. A chain-of- events chart shows the order in which the Your Turn Before you read this chapter, make a Pyramid FoldNote as described in steps of a process occur. Appendix A. Label the sides of the pyramid Your Turn In Section 3, you will read with “Igneous rock,” “Sedimentary rock,” about the formation of sedimentary rocks. and “Metamorphic rock.” As you read the Make a chain-of-events chart like the one chapter, define each type of rock, and write started below to describe compaction, one characteristics of each type of rock on the of the processes that form sedimentary appropriate side of the pyramid. rock. Use as many boxes as you need to record all steps of the process. Igneous rock In a sediment deposit, there are open spaces between the pieces of Sedimentary rock sediment. Note Taking Summarizing Ideas Summarizing the 3 Many paragraphs start or end with a content of each paragraph or set of sentence that summarizes the main idea paragraphs under a heading is a simple way of the paragraph. to take notes. A few tips on summarizing are Your Turn As you read each section, take listed below. notes by summarizing the main ideas. You 1 Summary statements should be short, may add structure to your notes by also but fully express the idea. writing the section title and red headings in 2 Use the green subheadings for guidance the appropriate places. in forming summary statements. For more information on how to use these and other tools, see Appendix A. 134 Chapter 6 Rocks hq10sena_rxstoolx.indd 134 PDF 8/15/08 8:16:35 AM SECTION 1 Rocks and the Rock Cycle Keyey Ideasdeas Keyey TermsTeesrms WhyWhy ItIt MattersMatte rs ❯ Identify the three major types of rock, and rock cycle Some rocks crumble and explain how each type forms. Bowen’s reaction others make for solid ❯ Summarize the steps in the rock cycle. series buildings. The physical ❯ and chemical properties Explain Bowen’s reaction series. of rock are determined ❯ Summarize the factors that affect the stability of by the conditions under rocks. which the rock forms. The material that makes up the solid parts of Earth is known as rock. Rock can be a collection of one or more minerals, or rock can be made of solid organic matter. In some cases, rock is made of solid matter that is not crystalline, such as glass. Geologists study the forces and processes that form and change the rocks of Earth’s crust. Based on these studies, geologists have classified rocks into three major types by the way the rocks form. Three Major Types of Rock Volcanic activity produces igneous rock. The word igneous is derived from a Latin term that means “from fire.” Igneous rock forms when magma, or molten rock, cools and hardens. Magma is called lava when it is exposed at Earth’s surface. Over time, natural processes break down all types of rock into small fragments. Rocks, min- Figure 1 These rocks are examples of eral crystals, and organic matter that have been the three major rock types. broken into fragments are known as sediment. Sediment is carried away and deposited by water, Sandstone (sedimentary) ice, and wind. When these sediment deposits are compressed, cemented together, and harden, sedimentary rock forms. Gneiss (metamorphic) Certain forces and processes, including tremen- dous pressure, extreme heat, and chemical pro- cesses, also can change the form of existing rock. The rock that forms when existing rock is altered is metamorphic rock. The word meta- morphic means “changed form.” Figure 1 shows an example of each major type of rock. Granite (igneous) 135 hq10sena_rxssec1.indd 135 PDF 8/15/08 8:18:45 AM Sedimentary rock Figure 2 The rock cycle illustrates the changes that igneous, sedimentary, and n tio M metamorphic rocks undergo. ta e n lt e in m E e g Keyword: HQXRXSF2 r c a o e n d s r d n i u a o c s o , s n o n e , o r l i d i p n t e i g s d p o n o p a s i e e t d r i o u , t n n a , r o a i e n s p d o m r e c E t e g m in g e n n a t h a C t io n Melting and coo ling Metamorphic rock Igneous rock Ch an re gi su ng pres temperature and The Rock Cycle Any of the three major types of rock can be changed into another of the three types. Geologic forces and processes cause rock to change from one type to another. This series of changes is called rock cycle the series of the rock cycle, which is shown in Figure 2. processes in which rock forms, One starting point for examining the steps of the rock cycle is changes from one type to another, is destroyed, and forms igneous rock. When a body of igneous rock is exposed at Earth’s again by geological processes surface, a number of processes break down the igneous rock into sediment. When sediment from igneous rocks is compacted and cemented, the sediment becomes sedimentary rock. Then, if sedi- mentary rocks are subjected to changes in temperature and pres- sure, the rocks may become metamorphic rocks. Under certain temperature and pressure conditions, the metamorphic rock will melt and form magma. Then, if the magma cools, new igneous rock will form. Much of the rock in Earth’s continental crust has probably passed through the rock cycle many times during Earth’s history. However, as Figure 2 shows, a particular body of rock does not always pass through each stage of the rock cycle. For example, www.scilinks.org igneous rock may never be exposed at Earth’s surface where the Topic: The Rock Cycle Code: HQX1319 rock could change into sediment. Instead, the igneous rock may change directly into metamorphic rock while still beneath Earth’s surface. Sedimentary rock may be broken down at Earth’s surface, and the sediment may become another sedimentary rock. Metamorphic rock can be altered by heat and pressure to form a different type of metamorphic rock. 136 Chapter 6 Rocks hq10sena_rxssec1.indd 136 2/23/09 8:48:52 AM Properties of Rocks All rock has physical and chemical properties that are deter- mined by how and where the rock formed. The physical character- istics of rock reflect the chemical composition of the rock as a whole Chain-of-Events Chart and of the individual minerals that make up the rock. The rate at Make a chain-of-events chart to which rock weathers and the way that rock breaks apart are deter- show each step of the discon- tinuous reaction series mined by the chemical stability of the minerals in the rock. of Bowen’s reaction series. Remember to Bowen’s Reaction Series use as many boxes In the early 1900s, a Canadian geologist named N. L. Bowen as you need to show began studying how minerals crystallize from magma. He learned all steps. that as magma cools, certain minerals tend to crystallize first. As these minerals form, they remove specific elements from the Academic Vocabulary magma, which changes the magma’s composition. The changing remove (ri MOOV) to take away or composition of the magma allows different minerals that contain eliminate different elements to form. Thus, different minerals form at differ- ent times during the solidification (cooling) of magma, and they generally form in the same order.
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