igneous
Pumice
Pumice, a highly vesicular volcanic glass, commonly rhyolitic to dacitic in composition
AI-generated identification · may be incorrectLight gray, rough, and full of small gas-bubble holes; typically glassy to dull, with no visible crystal structure or cleavage. Hardness is about 5–6 Mohs, though it can crumble; often unusually lightweight and may float when dry.
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Physical properties
Light gray, rough, and full of small gas-bubble holes; typically glassy to dull, with no visible crystal structure or cleavage. Hardness is about 5–6 Mohs, though it can crumble; often unusually lightweight and may float when dry.
Formation & geological history
Forms when gas-rich lava erupts and cools rapidly, trapping bubbles in volcanic glass. It is geologically young volcanic material, found near explosive eruptions and in deposits redeposited by water.
Uses & applications
Used as an abrasive and polishing material, lightweight aggregate, and soil amendment; also used in personal-care products and landscaping.
Geological facts
Its many vesicles make pumice one of the few rocks that can float; waterlogging eventually makes it sink.
Field identification & locations
Look for a porous, lightweight volcanic rock with abundant cavities and a gritty texture. Common around volcanic regions, including the Mediterranean, Iceland, and the western United States; the pictured specimen appears consistent with pumice.
