igneous
Pumice
Pumice (extrusive volcanic glass)
Hardness: 5-6 (but very brittle); Color: Grey, light gray, or cream; Luster: Dull to pearly; Crystal structure: Amorphous/Vesicular; Specific Gravity: 0.25-0.90 (often floats in water)
- Hardness
- 5-6 (but very brittle)
- Color
- Grey, light gray, or cream
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 (but very brittle); Color: Grey, light gray, or cream; Luster: Dull to pearly; Crystal structure: Amorphous/Vesicular; Specific Gravity: 0.25-0.90 (often floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles (vesicles) as it solidifies.
Uses & applications
Used as an abrasive in soaps (pumice stones), polishes, pencil erasers, and for stonewashed jeans. Also used in lightweight concrete, horticulture as a soil amendment, and for skin exfoliation.
Geological facts
Pumice is the only rock that can float on water because of its high porosity. Large eruptions can create 'pumice rafts' that float in the ocean for years, sometimes spanning hundreds of miles.
Field identification & locations
Identify by its extremely lightweight feel, highly porous (vesicular) texture, and ability to float in water. It is commonly found in areas of recent volcanic activity or in sedimentary deposits near volcanoes.
