igneous
Porphyritic Rhyolite
Rhyolite (Porphyritic texture)
Features larger crystals (phenocrysts) embedded in a fine-grained matrix. Hardness approximately 6-7 on Mohs scale. Colors range from light gray to tan or pink. Dull to earthy luster with glassy phenocrysts.
Identified More igneous →
Explore Porphyritic Rhyolite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Features larger crystals (phenocrysts) embedded in a fine-grained matrix. Hardness approximately 6-7 on Mohs scale. Colors range from light gray to tan or pink. Dull to earthy luster with glassy phenocrysts.
Formation & geological history
Formed from the rapid cooling of silica-rich magma or lava at or near the Earth's surface, where early-shaping crystals are trapped in a quickly solidifying groundmass.
Uses & applications
Primarily used as construction aggregate, decorative stone, and occasionally in the production of abrasive materials or stone tools in prehistoric times.
Geological facts
Rhyolite has the same chemical composition as granite but cooled much faster. If it had cooled even more quickly without crystal formation, it would have become obsidian.
Field identification & locations
Identify by the dual grain size: small visible crystals of quartz or feldspar set against a very fine, sandpaper-like background. Common in volcanic arcs and continental blowout regions.
