igneous
Pumice
Pumice (Amorphous volcanic glass)
Hardness: 5-6 (Mohs); Color: white, cream, light grey; Luster: vitreous to dull; Crystal structure: none (vesicular glass); Specific gravity: exceptionally low (often floats in water)
- Hardness
- 5-6 (Mohs)
- Color
- white, cream, light grey
- Luster
- vitreous to dull
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Physical properties
Hardness: 5-6 (Mohs); Color: white, cream, light grey; Luster: vitreous to dull; Crystal structure: none (vesicular glass); Specific gravity: exceptionally low (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 bubbles (vesicles) trapped in glass.
Uses & applications
Used as an abrasive in cleaning and personal care (pumice stones), lightweight aggregate in concrete, horticultural soil additives, and in stone-washing textiles like denim.
Geological facts
Pumice is the only rock that can float on water due to its air-filled pores. After massive eruptions, 'pumice rafts' can float on the ocean for years and travel thousands of miles.
Field identification & locations
Identify by its 'sponge-like' vesicular texture and extreme lightness. Common in volcanic regions like Italy, Turkey, and the Cascades in the USA. If it floats, it's likely pumice.
