igneous
Rhyolite porphyry
Porphyritic rhyolite, a silica-rich volcanic rock; exact identification requires closer examination
AI-generated identification · may be incorrectPink-brown, rough and weathered, with pale and reddish crystals or fragments in a finer matrix. Likely quartz and feldspar; hardness is roughly 6–7 Mohs, but a photo cannot establish mineral content or crystal structure reliably.
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Physical properties
Pink-brown, rough and weathered, with pale and reddish crystals or fragments in a finer matrix. Likely quartz and feldspar; hardness is roughly 6–7 Mohs, but a photo cannot establish mineral content or crystal structure reliably.
Formation & geological history
Formed when silica-rich lava cooled at or near the surface, producing conspicuous larger crystals in a finer groundmass. Rhyolites occur in volcanic regions of many ages; this specimen’s age and locality cannot be determined from the image.
Uses & applications
Mainly a collectible or teaching specimen; rhyolite may also be used as crushed stone or building stone where suitable.
Geological facts
The visible contrasting grains suggest a porphyritic texture, but the lumpy, weathered surface makes a firm identification uncertain.
Field identification & locations
Look for a fine-grained, silica-rich groundmass with quartz and feldspar crystals; inspect a fresh, unweathered surface and test hardness for confirmation. Common in volcanic belts worldwide.
