Lab06_Rocks

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University of Massachusetts, Amherst *

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100

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Geology

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Oct 30, 2023

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Name: _____________________________________ Section: _______ Laboratory 6: Rocks and Minerals Description: This lab gives you an opportunity to examine common rocks and minerals found throughout the world. Minerals are inorganic substances with specific chemical compositions and crystalline structures. Different minerals have different properties, such as color, shape, density, and degree of resistance to weathering. Rocks are aggregates of minerals; they share many of the properties of the minerals that comprise them, but also have properties that derive from the way they were formed. Rocks can be categorized into three classes based on their manner of formation: igneous, sedimentary, and metamorphic. In this lab you will examine rocks from each of these three classes, identify similarities and differences among them, and answer questions about how and where they formed. Key Terms: Rock Mineral Felsic Mafic Igneous Intrusive Extrusive Sedimentary Depositional environment Metamorphic Learning Outcomes: At the conclusion of this exercise, you will be able to: 1. Identify common minerals based on their color and crystalline structure. 2. Name common igneous rocks and identify the minerals of which they are composed. 3. Identify common sedimentary rocks, characterize the particle size of sediment of which they are composed, and be able to explain the depositional environment in which they were originally deposited. 4. Identify common metamorphic rocks, explain the process through which they were metamorphosed, and identify the original rock type from which they were formed. 7-1

Station 1: Minerals The following graph shows general relationships between six minerals and gives a short description of the important characteristics of each. Use the images provided in the “MineralsImage2” file in Canvas under the Lab 6 submodule in Module 7 Temperature of Formation Color Resistance to Weathering Compositio n Name Description 1200 o C Dark Weak Mafic (Fe, Mg) Olivine Colored as its name suggests Augite Black, angular Biotite Black, thin sheets Orthoclase Pink, long crystals Muscovite Clear/white, thin sheets 600 o C Light Strong Felsic (Si, Al) Quartz Clear/white, angled crystals 1. Identify each of the minerals based on its characteristics : a. ____________________ b. ____________________ c. ____________________ d. ____________________ e. ____________________ f. ____________________ 2. Compare the following pairs of minerals. For each, circle the mineral that will weather most easily. a. quartz or augite d. olivine or augite b. muscovite or olivine e. biotite or muscovite c. orthoclase or biotite f. quartz or olivine 7-2

3. Using what you know about the resistance of minerals to weathering, explain why quartz is the most common mineral in beach sand. 4. As a body of molten rock cools, certain minerals will form before other minerals. Write the names of the following minerals in the order in which they form during cooling and solidification. a. quartz, biotite, muscovite, augite ______________________________________________________ b. olivine, muscovite, biotite ______________________________________________________ c. augite, quartz, orthoclase, olivine ______________________________________________________ Station 2: Igneous Rocks The following table shows common characteristics of igneous rocks. Use the image provided in the “IgneousRocksimages” file in Canvas under the Lab 6 submodule located in Module 7. 5. Identify each of the rocks based on its characteristics using the images in the “IgeneousRocksimage” file. a. ____________________ b. ____________________ c. ____________________ d. ____________________ e. ____________________ 7-3 Intrusive (large crystals) Granite Diorite Gabbro Extrusive (small crystals) Rhyolite Andesite (not shown) Basalt Light Color Felsic (Si, Al) Mafic (Fe, Mg) Dark Color

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6. Compare granite with rhyolite: a. Which has larger crystals? b. Are the mineral compositions of granite and rhyolite similar or different? Explain. c. Which of these rocks took longer to cool and solidify? What does your answer tell you about where these rocks cooled and solidified? 7. Where in Wyoming would you be likely to find extrusive igneous rocks? 8. Hawaii is famous for its volcanoes and black sand beaches. a.) What kind of rock would you expect to be most common in Hawaii? b.) What minerals make up this rock? 7-4

Station 3: Sedimentary Rocks Clastic sedimentary rocks are classified based on the size of their constituent particles. Prior to being collected together and formed into rocks, these particles are transported by a variety of processes (wind, rivers, waves, ocean currents). Small particles can be transported relatively easily, in low-energy environments, while large particles are only mobile in high-energy environments. Shale Sandstone Conglomerate Small particles Large Particles Low-energy High-energy Clay, Silt Sand Gravel 9. Identify each of the given sedimentary rocks using the “SedimentaryRocksimage” file in Canvas under the Lab 6 submodule in Module 7. In addition to the rocks above, limestone is also included. Rock Name C. ____________________ D. ____________________ E. ____________________ F. ____________________ 10. Compare shale, sandstone and conglomerate: Which has the most consistent size of its constituent particles? 11. Another kind of sedimentary rock, limestone, is formed from precipitation of CaCO 3 in low energy environments. The limestone samples here are from the Casper Formation in Wyoming. What does this fact tell us about the geologic history of Wyoming? 7-5

Station 4: Metamorphic Rocks Metamorphic rocks are formed by exposing pre-existing rocks to extreme heat and pressure beneath the Earth’s surface. Metamorphic rocks are often more dense and resistant to weathering than their non- metamorphic counterparts, they often have striations or exhibit deformed, stretched crystals. Use the images provided in the “Metamorphic Rocks Chart” file in Canvas under the Lab 6 submodule in Module 7. 12. Each pair of rock samples on the table includes a metamorphic rock and its non-metamorphic counterpart (the rock from which it formed). For each pair, name the metamorphic rock and describe the characteristics that differentiate it from the non-metamorphic rock. Non-Metamorphic Metamorphic Characteristics a. GRANITE b . LIMESTONE c. SHALE d . SANDSTONE 13. Explain how sandstone can become quartzite. 14. What minerals (not elements) comprise gneiss ? 7-6

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