igneous
Porphyritic Rhyolite
Extrusive igneous rock with felsic composition
AI-generated identification · may be incorrectHardness 6-7 on Mohs scale, reddish-brown groundmass with distinct lighter quartz or feldspar phenocrysts, aphanitic-porphyritic texture, and vitreous to dull luster.
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Physical properties
Hardness 6-7 on Mohs scale, reddish-brown groundmass with distinct lighter quartz or feldspar phenocrysts, aphanitic-porphyritic texture, and vitreous to dull luster.
Formation & geological history
Formed from the rapid cooling of silica-rich lava at or near the Earth's surface, often originating in volcanic domes and flows.
Uses & applications
Used primarily as crushed stone in construction, decorative landscaping, and occasionally as lapidary material for cabochons.
Geological facts
The distinct contrasting spots are known as phenocrysts, which began crystallizing beneath the surface before the final volcanic eruption.
Field identification & locations
Identify by contrasting light-colored mineral crystals embedded in a fine-grained reddish matrix; commonly found in ancient volcanic regions.
