igneous
Pumice
Pumice (Volcanic Rock)
Hardness: 5-6 (Mohs scale); Color: Light gray to white; Luster: Dull or silky; Structure: Highly vesicular (porous) with no visible crystals; Specific Gravity: less than 1.0 (floats in water).
- Hardness
- 5-6 (Mohs scale)
- Color
- Light gray to white
- Luster
- Dull or silky
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Light gray to white; Luster: Dull or silky; Structure: Highly vesicular (porous) with no visible crystals; Specific Gravity: less than 1.0 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when liquid lava is ejected into the air; rapid cooling and depressurization cause bubbles of trapped gas to expand, creating a frothy, glass-like texture.
Uses & applications
Used as an abrasive in cosmetics (pumice stones), heavyweight construction concrete, water filtration, stonewashing textiles like jeans, and as a soil amendment in horticulture.
Geological facts
Pumice is the only rock that can float on water due to its incredible porosity. Massive rafts of floating pumice have been known to span hundreds of miles in the ocean following underwater volcanic eruptions.
Field identification & locations
Identify by its extremely lightweight feel, light color, and characteristic 'pitted' or spongy surface. Found globally near active or extinct volcanic regions like Italy, Turkey, Greece, Iceland, and the Western USA.
