![21.0 Vesicular porphyritic rhyolite. Chafee County, Colorado. A granular aphanitic matrix containing scattered vesicles encloses black biotite and hornblende phenocrysts, as well as gray quartz and white alkali (K-rich) feldspar phenocrysts. Sample courtesy of Sonoma State University Geology Department. [Scale shows cm divisions.]](../21.0.JPG)
21.0 Vesicular porphyritic rhyolite. Chafee County, Colorado. A granular aphanitic matrix containing scattered vesicles encloses black biotite and hornblende phenocrysts, as well as gray quartz and white alkali (K-rich) feldspar phenocrysts. Sample courtesy of Sonoma State University Geology Department. [Scale shows cm divisions.]