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DePaul HON 225 - Quiz 6 key

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HON 225 October 22, 2014 Please print Quiz #6: 50 pts 1. (13 pts) Answer the following true or false questions. Please print clearly. a. T Metamorphic rocks form by alteration of pre-existing rocks under conditions of elevated temperature and/or pressure. b. F Granite is comprised of the minerals quartz, mica, and clay. c. F Country rock is rock found exclusively under farmland. d. F Sedimentary rocks may be derived from igneous rocks, but igneous rocks may not be derived from sedimentary rocks. e. T Basalt is a dark, fine-grained igneous rock that forms above ground. f. F Igneous rocks formed underground tend to have small crystals. g. F Feldspar is the primary mineral found in limestone. h. T Limestones react with acid by fizzing. i. F Extrusive igneous rocks are also known as plutonic. j. T The continents are made mostly of granite. k. F Foliation is a defining feature of sedimentary rocks. l. T First generation stars contained only H and He. m. T The CNO cycle describes nuclear fusion in nth generation stars. 2. (3 pts) Rewrite the following list of sedimentary rocks in order of decreasing grain or particle size: sandstone, conglomerate, shale conglomerate, sandstone, shale3. a. (2 pts) What is the one sedimentary rock that can occur in both clastic and precipitate forms? Limestone b. (2 pts) What is the distinct feature of pumice or scoria and what accounts for this feature? Air holes or vesicles are prevalent throughout the rock, from gassy lava. 4. (4 pts) Match the igneous rock with its description. a. 3 Granite 1. Dark in color, large crystals b. 1 Gabbro 2. Dark in color, small crystals c. 4 Rhyolite 3. Light in color, large crystals d. 2 Basalt 4. Light in color, small crystals Answer any three of the following five questions (numbers 5 through 9) for credit. Indicate clearly which three you wish graded by circling the question number. Additional questions may be answered for extra credit. 5. (4 pts) What is the difference between magma and lava? Magma is melted rock belowground; lava is magma that reaches the surface of the planet. 6. (4 pts) Describe two changes to water that might result in precipitate formation. Four ways were discussed in class: • Climate change (T changes): solubility decreases as T decreases • Evaporation: less water flows into a body of water over time than evaporates • Salinity changes: amount of dissolved NaCl could affect solubility of other salts • Changes to pH: acidity of water affects the solubility of some salts, such as CaCO3 7. (4 pts) What is meant by “contact” metamorphosis? A sketch might help. Country rock in contact with a high temperature source such as an underground magma chamber will undergo recrystallization (minerals change composition or grow larger).8. (4 pts) What are two ways that sufficient pressure to cause metamorphism might be attained? Burial and collision of continental plates 9. (4 pts) Describe the role of groundwater in the lithification process of sediments. A sketch might help. Groundwater passes through sediments, precipitating out dissolved salts (primarily CaCO3) onto the clastic rock grains. As layers of precipitate build up, the rock bits are cemented together, pushing out the last of the water. 10. (4 pts) How would you distinguish between gneiss and schist? Gneiss is coarser grained than schist – e.g., gneiss mineral components are visible to the eye 11. (10 pts) Stellar evolution. a. (2 pts) Using nuclide symbols, write the net nuclear fusion taking place in both 1st and nth generation stars. 4 1H = 4He b. (3 pts) What triggers ignition in a star (one sentence or less)? Gravitational collapse forces H fusion (P and T are extremely high) c. (2 pts) What initiates star death (one sentence or less)? The star runs out of H for fusion d. (3 pts) When are elements heavier than He formed (one sentence or less)? When the star runs out of H, increasing gravitational pressure forces He fusion (and other nuclear reactions) making heavier


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