igneous
Pumice or vesicular volcanic rock
Pumice; chiefly volcanic glass (silica-rich, composition commonly rhyolitic to dacitic)
AI-generated identification · may be incorrectLight tan, highly porous, dull to slightly silky surface; hardness about 5–6, with irregular fracture and very low density. The visible specimen appears vesicular, though the image is insufficient to confirm its exact mineral composition.
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Physical properties
Light tan, highly porous, dull to slightly silky surface; hardness about 5–6, with irregular fracture and very low density. The visible specimen appears vesicular, though the image is insufficient to confirm its exact mineral composition.
Formation & geological history
Forms when gas-rich lava erupts explosively and rapidly cools, trapping bubbles in volcanic glass; typically Quaternary to modern, though older deposits are widespread.
Uses & applications
Used as an abrasive, exfoliating stone, lightweight aggregate, concrete additive, horticultural soil amendment, and occasionally in decorative specimens.
Geological facts
Pumice can float initially because of abundant interconnected vesicles, although waterlogging may eventually make it sink. It is commonly confused with scoria, which is darker, denser, and more mafic.
Field identification & locations
Look for abundant rounded or elongated holes, very low weight, glassy fragments, and lack of visible large crystals; a streak or density test helps distinguish it from porous sedimentary rock. Common around explosive volcanic regions worldwide, including Italy, Iceland, Japan, New Zealand, and the western United States.
