Chapter 6 Lab Activity. Rock Identification. Chapter 6 Lab Activity. Laboratory Manual LAB SKILLS AND OBJECTIVES. Procedure. Part A: Igneous Rocks

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1 Rock Identification In this lab you will examine, classify, and identify several rock specimens. Igneous rocks you will observe include basalt, gabbro, granite, obsidian, pumice, rhyolite, and scoria. Sedimentary rocks you will observe include coal, rock salt, shell limestone, compact limestone, conglomerate, sandstone, and shale. And finally, the metamorphic rocks will include gneiss, schist, slate, quartzite, and marble. Procedure Part A: Igneous Rocks 1 Sort the igneous rock specimens by color into two groups: lightcolored (felsic) and dark-colored (mafic). 2 Sort the rocks in each color group into the following three texture groups: coarse-grained igneous rocks, composed of crystals that are large enough to be seen with the unaided eye; fine-grained igneous rocks consisting of mineral crystals that are too small to be seen with the unaided eye; and rocks with glassy texture containing no crystals. Note: rocks with porous texture are also considered glassy. 3 Write the name of each igneous rock listed above in the correct location on the chart below. Refer to the Summary: Igneous Rocks table on page 124 of your text as needed. 4 Place each rock inside the appropriate box on the chart below. Then use the chart to answer Analysis and Conclusions Questions 1 6. LAB SKILLS AND OBJECTIVES Examine, classify and identify several igneous, sedimentary, and metamorphic rocks. Compare and contrast characteristics of the three types of rocks. MATERIALS igneous rock specimens Summary: Igneous Rocks table on page 124 of your text hand lens or magnifying glass sedimentary rock specimens coarse sandpaper metamorphic rock specimens Igneous Rock Chart Texture Light-colored (felsic) rocks Dark-colored (mafsic) rocks glassy fine-grained coarse-grained Earth Science 27

2 Part B: Sedimentary Rocks 5 Using what you learned about sedimentary rocks on pages of your text, write the name of each sedimentary rock listed at the top of page 25 of the lab manual in the correct location on the Sedimentary Rock Chart. 6 Carefully examine the set of sedimentary rock specimens. Place each rock in the box on the chart below that matches its description. Then use the chart to answer Questions Sedimentary Rock Chart Clastic rocks Chemical rocks Organic rocks sand and gravel cemented microscopic grains of calcite, rock made from plant remains together, resembles concrete gray or tan in color, dense cemented sand grains (usually) natural form of salt, salty taste skeletons and shells of sea quartz), gritty feel animals compact mud, earthy odor, usually easily broken Part C: Metamorphic Rocks 7 In general, metamorphic rocks can be placed into one of two texture categories. Foliated (or banded) metamorphic rocks have a layered appearance. Nonfoliated metamorphic rocks are generally massive with no apparent layering. Carefully examine the set of the metamorphic rock specimens and separate those that appear foliated from those that appear nonfoliated. 8 Using what you learned about metamorphic rocks on pages of your text, write the name of each metamorphic rock listed at the top of page 25 of the lab manual in the correct location on the Metamorphic Rock Chart. 9 Place each rock in the box on the Metamorphic Rock Chart that matches its description. Use the chart to answer Questions Earth Science

3 Clastic rocks Metamorphic Rock Chart Chemical coarse grains, light and dark bands hard, dense, crystalline, fused quartz grains thin and parallel bands with wavy, uneven surfaces crystalline, visible crystals of calcite, often white or gray red, gray, green, or purple, very fine grained, splits into smooth, flat layers Analysis and Conclusions 1 Using a hand lens or magnifying glass, look carefully at the mineral grains in the specimen of granite. What minerals occur in granite? 2 3 What minerals would you expect to occur in rhyolite? Explain. What minerals can you identify in the specimen of gabbro? Explain. 4 What minerals would you expect to occur in basalt? Explain. Earth Science 29

4 5 Based on its color and texture, where would you place obsidian on the chart? Based on the information in the Summary: Igneous Rocks table in your textbook, where would you place obsidian on the chart? Explain why your second classification is the correct answer. 6 Compare the pumice and scoria. Why are the holes in the scoria larger than the holes in the pumice? (Hint: Gas bubbles can move more easily in thin lava than in thick lava.) 7 How are the particles that make up the conglomerate different from the particles in the sandstone or in the shale? 8 Look carefully at the largest grains in the conglomerate specimen. Of what mineral are they composed? 9 Using a hand lens or magnifying glass, examine a piece of sandpaper and the sandstone specimen. Why does the sandstone feel like sandpaper? 10 Of what mineral or minerals is the sandstone made? 11 In what way is the overall appearance of the shale different from that of the conglomerate and the sandstone? 30 Earth Science

5 12 What chemical test could be used to identify both of the limestones you examined? Explain your answer. 13 How do the two limestone specimens differ in appearance? 14 Examine the particles that make up the shell limestone. Are they whole or in fragments? Name any particles that you can recognize. 15 Is rock salt different from the mineral halite? Explain your answer. 16 What is the overall color of the coal? Is its surface shiny or dull? Are any fossils visible? 17 Why are fossils rare in conglomerates? 18 Note the light and dark bands in gneiss. Using a hand lens, try to identify quartz, feldspar, and either mica or hornblende in the bands. Which minerals make up the light bands and which ones make up the dark bands? 19 Many gneisses are believed to have formed from granites. Compare the minerals that occur in gneiss with those that occur in granite. Earth Science 31

6 20 How is gneiss different in appearance from granite? 21 Look at the specimen of schist. How do the color and thickness of its mineral bands compare with those in the specimen of gneiss? 22 Mica schist is the most common kind of schist. In it, the flakes of mica are all parallel and easily seen. Is your specimen a mica schist? Why or why not? 23 What sedimentary rock does slate most closely resemble? 24 How is the texture of marble different from the texture of quartzite? 25 How could mineral hardness be used to tell quartzite from marble? 26 How could dilute hydrochloric acid be used to tell quartzite from marble? 27 Excluding marble and quartzite, what general properties of appearance can be used to determine whether a rock is metamorphic, igneous, or sedimentary? 32 Earth Science