igneous
Pumice
Highly vesicular volcanic glass, typically rhyolitic to andesitic composition; mainly silicate glass with feldspar, quartz, and minor pyroxene/amphibole.
AI-generated identification · may be incorrectVery light gray, extremely porous, and dull to silky; hardness about 5–6 Mohs, with irregular fracture and no cleavage. Low density often allows it to float; the holes are gas vesicles frozen into lava.
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Physical properties
Very light gray, extremely porous, and dull to silky; hardness about 5–6 Mohs, with irregular fracture and no cleavage. Low density often allows it to float; the holes are gas vesicles frozen into lava.
Formation & geological history
Forms when gas-rich magma erupts explosively and rapidly decompresses, producing frothy lava that cools quickly. It is generally Quaternary to modern, though pumice occurs throughout volcanic geologic history.
Uses & applications
Used as an abrasive, exfoliant, lightweight aggregate, concrete additive, horticultural soil amendment, and occasionally in decorative stone products.
Geological facts
Pumice is volcanic glass rather than a fully crystalline rock. Its abundant connected vesicles distinguish it from denser scoria, which is usually darker and basaltic.
Field identification & locations
Identify it by its exceptionally low weight, pale color, rough frothy texture, and ability to float briefly; common sources include volcanic islands and explosive-ash deposits worldwide. The pictured specimen could also be porous tuff or weathered scoria, but its pale color favors pumice.
