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A sample of rhyodacite from Slovakia

Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium-rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate-colored matrix. Rhyodacite is a high silica rock and often exists as explosive pyroclastic volcanic deposits.

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