igneous
Likely rhyolite or rhyolitic porphyry pebble
Rhyolite, a silica-rich volcanic rock; exact identification is uncertain from the photo
AI-generated identification · may be incorrectSmall, rounded, mottled pink, gray, and brown specimen with a fine-grained groundmass and possible pale feldspar crystals. Rhyolite is typically about 6–7 Mohs, has a vitreous-to-dull luster, and lacks prominent cleavage; density is commonly 2.3–2.7 g/cm³.
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Physical properties
Small, rounded, mottled pink, gray, and brown specimen with a fine-grained groundmass and possible pale feldspar crystals. Rhyolite is typically about 6–7 Mohs, has a vitreous-to-dull luster, and lacks prominent cleavage; density is commonly 2.3–2.7 g/cm³.
Formation & geological history
Forms when silica-rich lava cools rapidly at or near Earth’s surface; rhyolites occur in volcanic terrains of many ages, from ancient to recent.
Uses & applications
Rhyolite is used as crushed aggregate and occasionally as decorative stone; this pebble is mainly suitable for collecting.
Geological facts
Rhyolite is the volcanic equivalent of granite, but its crystals are usually much finer because lava cools faster than magma underground.
Field identification & locations
Look for a fine-grained, silica-rich rock with pale feldspar or quartz spots; similar colors can occur in several volcanic rocks, so a close examination or testing is needed for certainty. Found in volcanic regions worldwide.
