igneous
Pumice
Pumice (Amorphous volcanic glass)
Hardness: 5-6 (Mohs scale), Color: White, cream, or light grey, Luster: Dull to pearly, Crystal Structure: Amorphous/Vesicular, Specific Gravity: 0.25-1.2 (often floats in water)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: White, cream, or light grey, Luster: Dull to pearly, Crystal Structure: Amorphous/Vesicular, Specific Gravity: 0.25-1.2 (often floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization create a foamy texture trapped in glass.
Uses & applications
Abrasives in soaps and beauty products (pumice stones), lightweight aggregate in concrete/cinder blocks, horticulture for soil aeration, and stone-washing textiles (jeans).
Geological facts
Pumice is the only rock that can reliably float on water for long periods due to its high porosity. Large eruptions can create 'pumice rafts' that drift for miles across oceans.
Field identification & locations
Identifiable by its extremely light weight, light color, and 'sponge-like' appearance full of tiny holes (vesicles). Found in volcanic regions like the Cascades, Italy, or Iceland.
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