![21.1 Porphyritic rhyolite. Churchill County, Nevada. Pink, granular aphanitic matrix encloses gray, glassy quartz phenocrysts and a few white alkali feldspar (sanidine -?) phenocrysts. Sample courtesy of Sonoma State University Geology Department. [Scale shows cm divisions.]](../21.1.JPG)
21.1 Porphyritic rhyolite. Churchill County, Nevada. Pink, granular aphanitic matrix encloses gray, glassy quartz phenocrysts and a few white alkali feldspar (sanidine -?) phenocrysts. Sample courtesy of Sonoma State University Geology Department. [Scale shows cm divisions.]