igneous
Pumice
Vesicular volcanic glass, predominantly rhyolitic to dacitic composition
AI-generated identification · may be incorrectVery light, porous, pale gray to beige, with a dull to glassy luster and abundant vesicles; hardness about 5–6 Mohs, no cleavage, and low specific gravity—often able to float. The specimen appears weathered or sediment-coated.
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Physical properties
Very light, porous, pale gray to beige, with a dull to glassy luster and abundant vesicles; hardness about 5–6 Mohs, no cleavage, and low specific gravity—often able to float. The specimen appears weathered or sediment-coated.
Formation & geological history
Forms when gas-rich felsic lava cools rapidly during explosive volcanic eruptions, trapping bubbles in volcanic glass; individual pieces may be geologically young, from Quaternary eruptions, or older. Common around volcanic islands, ash deposits, and beaches.
Uses & applications
Used as an abrasive, lightweight concrete aggregate, horticultural soil additive, filtration material, and cosmetic exfoliant; attractive pieces are minor collector specimens.
Geological facts
Pumice is not a mineral because its glass is largely amorphous rather than crystalline. Its extreme vesicularity distinguishes it from denser volcanic rocks such as rhyolite.
Field identification & locations
Identify it by very low density, frothy texture, sharp irregular pores, and light color; test whether it floats, though waterlogged pieces may sink. Common worldwide in volcanic regions, including Italy, Greece, Turkey, Japan, New Zealand, and the western United States.
