igneous
Pumice
Pumice (Volcanic silicate glass)
Hardness: 5-6 Mohs scale; Color: grayish-green/light gray; Luster: dull to earthy; Structure: highly vesicular (pitted with gas bubbles); light enough to float in water initially.
- Hardness
- 5-6 Mohs scale
- Color
- grayish-green/light gray
- Luster
- dull to earthy
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Physical properties
Hardness: 5-6 Mohs scale; Color: grayish-green/light gray; Luster: dull to earthy; Structure: highly vesicular (pitted with gas bubbles); light enough to float in water initially.
Formation & geological history
Formed during explosive volcanic eruptions where magma is violently ejected into the air; rapid cooling and depressurization trap gas bubbles, creating a frothy glass texture.
Uses & applications
Used as an abrasive in soaps, foot stones (pumice stones), stone-washing jeans, and as a lightweight aggregate in concrete/plaster.
Geological facts
Pumice is the only rock that can float on water due to its extremely low density and numerous trapped air pockets. Large rafts of floating pumice can persist for years following major eruptions.
Field identification & locations
Identify by its extremely lightweight feel and vesicular (sponge-like) texture. Found in volcanic regions like the Cascades, Iceland, or Italy.
