igneous
Pumice
Pumice (Volcanic Rock / Glass Froth)
Hardness: 6 on the Mohs scale, Color: White, grey, yellowish, or brownish, Luster: Earthy to silky, Crystal structure: Amorphous (volcanic glass), Cleavage: None, Specific gravity: Less than 1.0 (floats on water due to high porosity).
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Physical properties
Hardness: 6 on the Mohs scale, Color: White, grey, yellowish, or brownish, Luster: Earthy to silky, Crystal structure: Amorphous (volcanic glass), Cleavage: None, Specific gravity: Less than 1.0 (floats on water due to high porosity).
Formation & geological history
Formed from explosive volcanic eruptions where felsic or intermediate magma containing dissolved gases depressurizes rapidly, causing the lava to foam and instantly cool into a frothy glass matrix.
Uses & applications
Used in lightweight concrete, abrasive soaps, pumice stones for personal care, horticulture as a soil amendment, and stonewashing jeans.
Geological facts
Pumice is the only rock that can float on water. When Krakatoa erupted in 1883, it produced massive rafts of floating pumice that drifted across the ocean for years.
Field identification & locations
Easily identified by its extremely light weight relative to its size and its vesicular, spongy texture riddled with tiny gas cavities. Found worldwide near active or ancient volcanic regions.
