Chapter+4a+-+Igneous+Rocks

Extrusiveigneous rockscoolrapidlyand arefinegrained

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Unformatted text preview: from lava in the air. Extrusive igneous rocks cool rapidly and are fine­grained. (aphanitic) Intrusive igneous rocks cool slowly, allowing large, coarse crystals to form. (phaneritic) Some phenocrysts grow large, but the remaining melt cools faster, forming smaller crystals during an eruption. (porphyritic) Intrusive and Extrusive Igneous Equivalents Thought questions for this chapter Thought How would you classify a coarse-grained igneous rock How that contains about 50 percent pyroxene and 50 percent olivine? peridotite peridotite Thought questions for this chapter Thought Assume that a magma with a certain ratio of calcium to Assume sodium starts to crystallize. If fractional crystallization occurs during the solidification process, will the plagioclase feldspars formed after complete crystallization have the same rat...
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