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| Cooling Environments for Igneous Rocks | ||||||||||||
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| This is an attempt to convey some of the things implied by crystal grain sizes in igneous rocks. "Phaneritic" means "the smallest grains are visible to the naked eye". "Aphanitic" means "the smallest grains are not visible to the naked eye". "Porphyritic" means "there are two distinct sizes of crystal grains present". "Pyroclastic" means "composed of firey fragments". "Glassy" means "this cooled too fast for crystal grains to form". "Vesicular" means "there are holes that were once gas bubbles". Volcanic rocks cool at or on surface. Plutonic rocks cool underground. | ||||||||||||
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