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Rhyolite is an igneous, volcanic (extrusive) rock, of felsic
composition, with aphanitic to porphyritic texture. Mineral assembly is usually quartz, alkali
feldspar and plagioclase (in a
ratio > 1:2). Biotite and pyroxene
are common accessory minerals.
Rhyolite can be considered as the extrusive equivalent to the plutonic granite rock. Due to their high content of silica, rhyolite form highly viscous lavas. They can also occur as breccias or in volcanic necks and dikes.
Like obsidian, rhyolites frequently show flow, spherulitic, nodular, and
lithophysal structures.
See also: igneous rocks, list of rocks, granite
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