![21.2 Porphyritic rhyolite. Salem, Massachusetts. Phenocrysts of gray to red, hematite-stained quartz and white alkali feldspar and small phenocrysts of black to reddish-black weathered ferromagnesian minerals occur in the red-stained crystalline matrix of this rhyolite. Sample in Sonoma State University Geology Department Collections. [Scale shows cm divisions.]](../21.2.JPG)
21.2 Porphyritic rhyolite. Salem, Massachusetts. Phenocrysts of gray to red, hematite-stained quartz and white alkali feldspar and small phenocrysts of black to reddish-black weathered ferromagnesian minerals occur in the red-stained crystalline matrix of this rhyolite. Sample in Sonoma State University Geology Department Collections. [Scale shows cm divisions.]