igneous
Pumice
Vesicular volcanic glass (primarily SiO2)
Hardness: 5-6 (Mohs scale), Color: Light gray, tan, cream, or brownish with dark inclusions, Luster: Dull to silky, Texture: Highly vesicular with low density (often floats on water), Specific Gravity: ~0.25 to 0.9
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Light gray, tan, cream, or brownish with dark inclusions, Luster: Dull to silky, Texture: Highly vesicular with low density (often floats on water), Specific Gravity: ~0.25 to 0.9
Formation & geological history
Formed during explosive volcanic eruptions when highly gas-charged, felsic to intermediate magma cools rapidly, trapping gas bubbles (vesicles) before the lava solidifies.
Uses & applications
Widely used in abrasive cleaners, stone-washing denim, lightweight concrete aggregate, horticulture as a soil amendment, and cosmetics (foot scrub stones).
Geological facts
Pumice is the only rock that can float on water due to its extreme porosity created by trapped volcanic gases during rapid cooling.
Field identification & locations
Identify in the field by its light weight, porous sponge-like texture with tiny holes, light pale color, and ability to float on water. Commonly found along coasts near volcanic regions or volcanic deposits.
