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Unformatted text preview: Igneous Mineral Composition o Felsic rich in light-colored minerals orthoclase/plagioclase feldspar o Mafic rich in dark-colored ferromagnesian minerals augite, hornblende abundant feldspar plagioclase o Ultramafic composed chiefly of dark-colored ferromagnesian minerals olivine, pyroxene Texture o fine-grained coarse-grained pegmatitic (exceptionally coarse- grained, > 1 cm) o porphyry large and very small crystals (groundmass) larger crystals = phenocrysts o pegmatite all crystals are pegmatitic (> 1 cm) Cooling history o No crystals small large very large o Ext remely rapid rapid slow slow (and presence of water) Plutonic Rocks o Sill parallel to local st ructure o Dike across local st ructure o Batholiths enormous body of granit ic rock exposed at surface by erosion Stock small batholiths (< 100 km 2 ) Volcanic Rocks o Columnar joint polygonal columns developed in basalt as it cools and shrinks o Vesicles remnant gas bubbles in volcanic rock...
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This note was uploaded on 02/25/2011 for the course GEO 303 taught by Professor Leon during the Spring '08 term at University of Texas at Austin.
- Spring '08