igneous
Pumice
Pumice (Volcanic glass with vesicular texture)
Hardness: 6 (Mohs), Color: Light gray/white/cream, Luster: Dull to pearly, Texture: Vesicular (highly porous/cellular), Specific Gravity: 0.25 to 0.7 (floats on water)
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Physical properties
Hardness: 6 (Mohs), Color: Light gray/white/cream, Luster: Dull to pearly, Texture: Vesicular (highly porous/cellular), Specific Gravity: 0.25 to 0.7 (floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (magma) cools so rapidly that gas bubbles are trapped inside, creating a frothy glass structure. Common in convergent plate boundaries.
Uses & applications
Used as an abrasive in polishing and cleaning, in lightweight concrete blocks, as a soil additive (horticulture), for stonewashed denim, and in personal care (exfoliating pumice stones).
Geological facts
Pumice is the only rock that can float on water due to its air-filled pores. Large 'pumice rafts' can travel across oceans for thousands of miles following major volcanic eruptions.
Field identification & locations
Identify in the field by its extreme lightness (low density) and sponge-like appearance. Commonly found in areas with history of explosive volcanism such as the Lipari Islands or the Cascades.
