classification of igneous rocks filemineral composition basaltic rocks (mafic) - dark-colored, lower...
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Classification of Igneous Rocks
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Igneous Rock FormationIntrusive rock - form when magma cools and crystallizes below Earth’s surface
Also called plutonic rocks
Cools slowly - forms coarse grained rocks
Ex: granite
granitemagma
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Extrusive rock - form when magma cools and crystallizes on Earth’s surface
Also called volcanic rocks
lava cools quickly - forms fine grained rocks
Ex: scoria
scoria
Igneous Rock Formation
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Intrusive & Extrusive
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Mineral CompositionBasaltic rocks (mafic) - dark-colored, lower silica contents, and contain mostly plagioclase and pyroxene
gabbro
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Granitic rocks (felsic) - light-colored, high silica contents, and contain mostly quartz and feldspar
Mineral Composition
granite
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Mineral CompositionIntermediate rocks - have a composition somewhere in between basaltic and granitic, and consist mostly of plagioclase feldspar and hornblende
diorite
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Mineral CompositionUltrabasic (ultramafic) - rocks contain only iron-rich minerals such as olivine and pyroxene and are always dark
peridotite
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TextureTexture refers to size, shape, and distribution of crystals or grains that make up a rock
Ex: rhyolite is fine-grained, while granite is coarse-grained
rhyolite
granite
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Porphyritic RocksPorphyritic - texture characterized by large, well-formed crystals surrounded by finer-grained crystals of same mineral or different minerals
Indicates a complex cooling history during which a slowly cooling magma suddenly began cooling rapidly
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Vesicular RocksMagma contains dissolved gases that escape when pressure decreases
When lava is thick enough to prevent gas bubbles from escaping, holes called vesicles are left behind
Spongy appearance - vesicular texture
pumice
vesicular basalt