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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...