igneous
Pumice
Pumice (Amorphous volcanic glass)
Hardness: 5-6 Mohs; Color: White to light grey; Luster: Dull to silky; Structure: Vesicular (highly porous/bubbly); Specific Gravity: 0.25-0.9 (can float in water).
- Hardness
- 5-6 Mohs
- Color
- White to light grey
- Luster
- Dull to silky
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Physical properties
Hardness: 5-6 Mohs; Color: White to light grey; Luster: Dull to silky; Structure: Vesicular (highly porous/bubbly); Specific Gravity: 0.25-0.9 (can float in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles in a frothy glass structure.
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 incredible porosity and low density, though it will eventually sink as its pores fill with water.
Field identification & locations
Identify by its light weight and 'frothy' appearance; feels like hard foam. Often found in volcanic regions or washed up on shorelines near tectonic boundaries.
