Geology 6 Geology 006
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This 3 page Class Notes was uploaded by Omarah Lewis on Sunday September 18, 2016. The Class Notes belongs to Geology 006 at Los Angeles City College taught by Professor Lorentz in Fall 2016. Since its upload, it has received 29 views. For similar materials see Geology in Physical Science at Los Angeles City College.
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Date Created: 09/18/16
9/21/16 Rock Classification: Genetic Classification: based on the origin of a rock. Igneous Rocks: formed by solidification of melts. (melts: above ground=lava; below ground=magma) Sedimentary Rocks: Formed by cementing of grains from pre-existing rocks, or precipitation of minerals from water solution. (history of biology and climate preserved in the rock.) Metamorphic Rocks: Formed when pre-existing rock is changed by heat or pressure. The Rock Cycle: The cycle by which the above rocks transform into one another based on what’s happening above and below the Earth’s surface. Igneous rocks classification is based on composition and texture. (what minerals are in it and how big are they?) Classified by their % of Silica (SIO2) Felsic: 70% silica content, continental composition and light in color. Intermediate: 60% Silica content, mix of continental-oceanic composition. Mafic: 50% Silica content, ocean floor composition and dark in color. Ultra Mafic: less than 50% Silica, mantle composition. Texture: Coarse mineral crystals: slow cooling of melt below ground. (can be seen with the naked eye) Fine mineral crystals: fast cooling of melt above ground. (can’t be seen with the naked eye) Felsic: Intermediate: Mafic: Granite Diorite Gabbro Rhyolite Andesite Basalt Volcanic Glass: Obsidian: compact glass, usually black and shiny. Pumice: Frothy glass, light weight (can float in water) Sedimentary Rock Types Clastic: cemented together fragments and grains derived from pre-existing rocks. Chemical: composed of minerals that precipitate from water solutions. Size: Conglomerate- boulders (large rocks) Breccia- cobbles/pebbles Sandstone-sand compacted together. Siltstone: silt, rock pieces compacted together Shale- clay and mud compacted together. Chemical Sedimentary Rocks: Chert: formed from accumulation of plankton that grows silica shells. Dark Chert: flint stones (what’s used to start fires) Metamorphic Rocks: Slate: slight metamorphism of shale aligns internal minerals for a slight sheen. Compositional layering, may include other minerals like quartz, feldspar and garnets. Schist: Coarser grained rock contains visible mica. Gneiss (nice): Contains compositional layering often manifest as light/dark banding. Quartzite: Forms when sandstone is metamorphosed, quartz grains recrystallize and grow larger and weld into interlocking texture. Marble: Forms from recrystallization of limestone or dolostone. Uniform in texture and relative softness of calcite makes marbles ideal for sculpting.
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