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Geo Lab Midterm - Igneous • Mineral Composition o Felsic...

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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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Geo Lab Midterm - Igneous • Mineral Composition o Felsic...

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