Definition of rhyodacite
The extrusive equivalent of granodiorite. The principal minerals, sodic plagioclase, sanidine, quartz, and biotite or hornblende, commonly occur as phenocrysts in a finely crystalline groundmass of alkali feldspar and quartz. Accessory minerals are apatite and magnetite, and occasionally augite.
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Locality Updated: Woodsboro, Frederick Co., Maryland, USAFrom Bill Cordua, 13th Dec 2013 02:30:58