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Rocks and the Rock Cycle El Capitan in Yosemite How did this form? www.nps.gov Classifying Rocks Igneous Sedimentary Metamorphic Based on how they formed Igneous Rock • Rock that forms from magma • Magma –mix of molten rock, gases and water vapor that forms underground • Magma flows from volcanoes as lava and then hardens http://pubs.usgs.gov/ publications/text/Krafla. html Two types of igneous rock • Intrusive rock - forms underground from hardened magma • Cool slowly – create crystals • Granite – cools slowly so crystals form • Extrusive Rock – forms at Earth’s surface • Cools quickly so no large crystals • Obsidian – cools very rapidly so atoms can’t make crystals Sedimentary Rock • Rock that forms over time as sediment is squeezed and cemented together • Pressure causes the layers to compress Three types of Sedimentary rock • Clastic • Chemical • Organic Clastic Rock • Sedimentary rocks that form from broken fragments of other rocks • Ex. conglomerates Chemical Rock • Formed when minerals precipitate out of solution • Ex. Rock salt Organic Rock • Form due to organic processes • Ex. Calcium carbonate from marine shells • limestone Metamorphic rock • Rock that has been changed by temperature, pressure or reactions with hot water • Made from all three types of rock • Ex. Gneiss Rock Cycle • Series of processes in which rocks continuously change from one type to another • Caused by forces within the Earth and at the surface
