igneous
Pumice
Pumice (Amorphous volcanic glass)
Hardness: 5-6 (but brittle/crumbly); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (highly porous); Specific Gravity: 0.25 to 0.70 (floats in water).
- Hardness
- 5-6 (but brittle/crumbly)
- Color
- White, cream, or light grey
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 (but brittle/crumbly); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (highly porous); Specific Gravity: 0.25 to 0.70 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is violently ejected and cools rapidly, trapping gas bubbles in a frothy glass matrix.
Uses & applications
Used as an abrasive in soaps (Lava soap), foot stones for skin exfoliation, dental polishing, lightweight concrete aggregate, and stone-washing textiles like denim.
Geological facts
Pumice is the only rock that consistently floats on water due to its air-filled pores. After major eruptions, vast 'pumice rafts' can form in the ocean, drifting for thousands of miles.
Field identification & locations
Identify in the field by its extremely light weight, frothy 'sponge-like' appearance, and ability to float. Commonly found in volcanic regions like the Andes, Cascades, or Mediterranean.
