7.3 Families of Rocks Page 188

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1 7.3 Families of Rocks Page 188 PRESCRIBED LEARNING OUTCOMES compare the characteristics of Earth s core, mantle, and crust, and describe the formation of rocks KNOWLEDGE rocks are classified by how they are formed within the rock cycle and their mineral content SKILLS AND ATTITUDES investigate the use of models to show large scale systems ICT OUTCOMES work cooperatively using information technology tools apply predetermined search criteria to locate and retrieve information using information technology tools synthesize information from a variety of electronic sources for presentations develop interactive hypertext documents for presentations produce multimedia presentations SCIENCE BACKGROUND There are three basic types of rocks: igneous, sedimentary, and metamorphic. The classification system is based on how the rock was formed. Igneous Rock Magma is molten rock material deep under the surface of Earth. It is produced in the upper part of the mantle or the lowest part of the crust. If it emerges from cracks in Earth s surface, it is called lava. Magma that cools slowly deep in Earth s crust eventually solidifies to form intrusive igneous rock such as granite. These large intrusions can be later exposed by weathering and erosion, and form major mountains such as the Rockies. When molten rock cools and solidifies, it becomes mineral crystals. The size of the crystals depends on the rate of cooling; the slower the cooling, the larger the crystals. Igneous rock can be extremely coarse-grained, like granite; finegrained, like andesite; or glassy, like obsidian. Sedimentary Rock Sedimentary rock is most commonly formed through the compacting and cementing of sediment. Another way it is formed is by the crystallization of dissolved minerals. The process of forming crystals from dissolved minerals usually occurs in shallow parts of seas or in lakes in deserts. As water evaporates, the concentration of the solution increases. As the solution becomes supersaturated, the dissolved minerals come out of solution to form crystals that settle on the lake or ocean bottom. As this process continues, more crystals form and accumulate, eventually becoming sedimentary rock. Sedimentary rock can also be formed from biological materials or activity. For example, limestone (a rock made up of calcite CaCO 3 ) is formed mainly from the accumulation of the remains of marine invertebrate organisms (such as mollusks and corals) that have carbonate shells or exoskeletons. When these organisms die, their Time min Key Ideas Earth s crust is made up of three families of rocks: igneous, sedimentary, and metamorphic. Vocabulary magma igneous rock intrusive lava extrusive sediment sedimentary rock metamorphic rock Skills and Processes Observing Creating Models Lesson Materials per student about 1/4 cup each of clay or mud, sand, and very fine gravel or pebbles glass jar with lid water Program Resources SM 7.3 Families of Rocks BLM Three-Column Table Science Skills and Processes Rubric 1: Creating Models Science Skills and Processes Rubric 2: Creating Models Self- Assessment Nelson Science Probe 7 Web site Chapter 7 Old rocks can be recycled into new rocks. 365

2 Related Resources Geologists Notebook: Three Rocks (video). Vancouver, BC: B.C. Learning Connections Inc., (604) ; shells/exoskeletons fall to the sea bed and accumulate over long periods of time. Over geologic time, these accumulations are compressed and cemented together to form limestone. Sedimentary rocks are generally stratified, fine grained, or composed of fragments of older rocks. Metamorphic Rock Metamorphic rock is identified by the minerals it contains and by its texture. Metamorphic rock textures include Slaty cleavage: Minerals, such as mica, are aligned parallel to each other in fine crystalline rock. The rock splits readily along cleavage plains (e.g., slate). Schistosity: Minerals, such as mica, chlorite, and hornblende, are aligned (but not segregated) in easily visible parallel bands. The rock splits easily (e.g., schist). Mineral banding (gneissic texture): The minerals are separated into elongated bands and are therefore more easily identifiable (e.g., gneiss). The bands of granular minerals (e.g., quartz) alternate with bands of platy or elongated minerals (e.g., mica). TEACHING NOTES It is important that students actually see and examine different kinds of rocks as they are being discussed in class. A few sets that contain good samples of rocks from each family would be ideal. At a minimum, you should have six samples of each intrusive igneous, extrusive igneous, metamorphic, and sedimentary rocks that can be circulated around the class during the discussion. 1 Getting Started Have students examine a sample of an igneous, metamorphic, and a sedimentary rock, without providing names for them, and ask them to describe each one. Focus the discussion on how the rocks are different from one another. Ask students to skim the section, paying particular attention to headings to identify the three families of rocks. 2 Guide the Learning Read the Learning Tip about the term igneous. Discuss it using Reading and Thinking Strategies: Determine the Meanings of Key Scientific and Technical Terms. Follow the same strategy to discuss metamorphic later in the section. Read through each section, discussing the photos of rocks with students and reviewing properties of each that make it one of the three families of rocks. Pause at the Learning Tip on page 189 to allow students time to write down what they think is the difference between intrusive and extrusive igneous rocks, then check their ideas by rereading and looking at Figure 2 again. Pause at the Learning Tip on page 190. Have students examine Figure 7, noting the buildup of sediment layers. Arrange students in pairs to paraphrase for each other how sedimentary rock is formed. 366 Unit C: Earth s Crust

3 Have students complete Try This: Make Your Own Sediment. TRY THIS: MAKE YOUR OWN SEDIMENT Purpose Students will model the beginning stages of sedimentary rock formation. Notes Students do not need to use the same substances in the activity. A variety of substances will show the same results: that is, the substances will arrange themselves according to density, no matter where they came from or what they are. Have students use about a 1/4 cup measure of each ingredient in a 500 ml jar, then add 250 ml water. Have students draw a sketch of the results of the activity, labelling the different layers (sand, gravel, clay). Point out that a sketch is one way observations can be recorded. Make it explicit that this is a model for the beginning stages of the formation of sedimentary rock. Ask them what would have to happen to turn their layered sediments into sedimentary rock. Suggested Answers The largest, heaviest particles will be at the bottom, with the smaller particles above. Relate this to density: that is, the denser particles sink to the bottom. For students who need additional support with the reading in this section, use SM 7.3 Families of Rocks. 3 Consolidate and Extend Show students the three rock samples from Getting Started and ask them to identify each as sedimentary, igneous, or metamorphic. Pairs or small groups of students can play a What Am I? game: for example, I am an igneous rock and I float. What am I? Assign the Check Your Understanding questions. When students have finished, have them share their answers with a partner and revise if needed. Provide students with BLM Three-Column Table to answer question 1. Chapter 7 Old rocks can be recycled into new rocks. 367

4 Technology Connections Have students work individually or with a partner to research one of the three rock families. Research should focus on how the rocks are formed, characteristics of those types of rocks, and examples of types of rocks found in this family. Students could present their findings through oral reports, posters, or multimedia presentations with supporting pictures and/or rock samples. CHECK YOUR UNDERSTANDING SUGGESTED ANSWERS 1. Students table may be similar to the following: Type of rock How it is formed Examples igneous extrusive intrusive sedimentary Igneous rock is formed from the hardening of liquid magma. Lava cools and hardens above ground as it emerges onto surface. Lava cools and hardens under the surface. Weathering breaks down rocks into small particles called sediment. Streams and rivers carry sediment to lakes and oceans. Sediment forms layers on lake or ocean floors. Pressure pushes the materials together, and dissolved minerals cement them together into rock. obsidian, pumice, basalt granite shale, sandstone, conglomerate, limestone metamorphic Heat and pressure within Earth change igneous and sedimentary rock into metamorphic rock. slate, marble, quartzite, gneiss, phyllite, schist 2. The difference between intrusive and extrusive igneous rock is that intrusive is formed by magma cooling within Earth, and extrusive is formed from magma that erupts as lava and cools on the surface of Earth. 3. The difference between minerals and rocks is that minerals are the building blocks of rocks. A rock can contain several different minerals. 4. The crystals in the middle of the geode are larger than those toward the outside because those in the middle have cooled more slowly. 368 Unit C: Earth s Crust

5 7.3 Igneous Rock LEARNING TIPLEARNING TIP Metamorphic Hot molten Rock rock under Earth s surface is called magma. Rock that The word metamorphic forms from the hardening of liquid magma is called igneous rock The word igneous When comes igneous or sedimentary rock becomes buried at a great depth, means changed from in form. the Latin word ignis, [IG-nee-us]. Most of Earth s surface is composed of igneous rock, It comes from the it is subjected to increased temperature and pressure. As well, magma meaning Greek fire. and igneous rock is still being formed today. words meta, meaning moving through Earth heats and squeezes the neighbouring rock. As a result, the rock If may the change. magma The cools changed rock is different from the original rock in underground, appearance or the in rock the minerals that it contains. Rock formed below is Earth s formed surface, is called when heat and pressure cause the properties of existing intrusive rocks igneous to change, rock. is called metamorphic rock. This type of igneous rock is Some metamorphic rocks have been changed so much that they seen on Earth s surface only no longer resemble the original rock, or parent rock. Often, however, after years of erosion have geologists can trace the relationship between a metamorphic rock and worn away the layers of its parent rock. For example, slate is a metamorphic rock that is formed rock over it. Stawamus from the sedimentary rock shale. Gneiss [NICE] is a metamorphic rock Chief near Squamish, that is formed from the igneous rock granite. Table 1 shows some types British Columbia is one of of metamorphic rocks and their parent rocks. the world s largest chunks Table 1 Metamorphic of granite, Rocks a common intrusive igneous rock after, and morphe, meaning form. The root metamorph is used in other areas of science as well. For example, the change in form of a caterpillar into a butterfly is called metamorphosis. Families of Rocks There are many different minerals, but they are usually found mixed together in rocks. For example, granite contains mica, quartz, and feldspar. Geologists classify rocks into three families based on how they are formed. These are igneous, sedimentary, and metamorphic rock. Parent rock Metamorphic rock (Figure 1). shale slate (sedimentary) If the magma is forced out onto Earth s surface, it is called lava. Igneous rock that is formed on Earth s surface when the lava cools granite gneiss (igneous) is called extrusive igneous Figure 1 The Stawamus Chief is popular with climbers. rock. Basalt is extrusive Many Aboriginal groups have special stories igneous rock that is common and legends about unique features like the in British Columbia. Stawamus Chief. Reading and Thinking Strategies: Determine the Meanings of Key Scientific and Technical Terms Explain to students that many words in science come from Greek and Latin words. Have them look at the Learning Tip to note that the Latin word is written in italics. Explain that when we use words from other languages in English writing, we always italicize them. Ask students why the term igneous is based on the Latin word for fire. Ask them what other words they know that might have been made from the Latin word ignis. (Two examples are, ignition and ignite). Discuss how they might have been able to figure out what igneous meant if they did not know the Latin root. (by thinking of the meanings of ignition and ignite). Follow the same strategy for the Learning Tip on page 192. Students might be familiar with the slang term morph. 188 Unit C Earth s limestone Crust marble (sedimentary) sandstone (sedimentary) quartzite 192 Unit C Earth s Crust Extra Support The student book presents many new words and concepts. Students who need extra experience with the vocabulary and concepts in this section would benefit from supplemental materials, such as a videos, field trips, and hands-on activities, wherever feasible. For students who need additional support with the reading in this section, use SM 7.3 Families of Rocks. Meeting Individual Needs ASSESSMENT FOR LEARNING What To Look For in Student Work Evidence that students can describe how families of rocks are formed and give examples (e.g., igneous, sedimentary, and metamorphic rocks) create models (e.g., models of sediment) use technical language correctly (magma, igneous rock, intrusive, lava, extrusive, sediment, sedimentary rock, metamorphic rock) Suggestions for Teaching Students Who Are Having Difficulty Ask questions after each subsection to draw out information about how each family of rocks was formed: for example, What is magma? What is igneous rock made from? Can magma cool under the ground? What rock is formed when this happens? Chapter 7 Old rocks can be recycled into new rocks. 369