ERTH 20 Lecture Notes - Lecture 18: Phanerite, Extrusive Rock, Viscosity
2 Dec 2020
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Document Summary
4 major types of magma names based on percentage of silica. Intrusive (deep-hotter) take long time to cool. Extrusive: magma has extruded onto earths surface- fast cooling. Lava flows or domes pyroclastic flows or deposits. Course grained texture: composed of mineral grains that are large enough to be identified without a microscope. Fine grained texture: composed of crsytals that are too small for individual minerals to be seen. Classificiation is based on composition and texture. It is less dense than the surrounding rocks. Speed of magma flow governed by viscosity. Viscosity most depends on amount of silica: viscosity- resistance to flow, less sio2 (mafic)- lower viscosity (runny magma, more sio2 (felsic)-higher viscosity (sticky magma) Pahoehoe- basalt lava flow with typical ropy texture. Geologists define four classes of sedimentary rock: clastic/detrial, biochemical, organic, chemical. Processes that turns existing rock into sedimentary rock: weathering, erosion, transport, deposition, lithification. Sediment and sedimentary rocks cover 80% of the earth"s surface.
