igneous
Pumice
Pumice (Volcanic Glass)
Hardness: 5-6 (but very brittle); Color: Pale grey, white, cream, or light green; Luster: Pearly to dull; Structure: Vesicular (highly porous) amorphous glass; Specific Gravity: less than 1.0 (floats in water).
- Hardness
- 5-6 (but very brittle)
- Color
- Pale grey, white, cream, or light green
- Luster
- Pearly to dull
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Physical properties
Hardness: 5-6 (but very brittle); Color: Pale grey, white, cream, or light green; Luster: Pearly to dull; Structure: Vesicular (highly porous) amorphous glass; Specific Gravity: less than 1.0 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (magma) is violently ejected and cools rapidly, trapping gas bubbles within the solidifying glass.
Uses & applications
Used as an abrasive in soaps (pumice stones), cosmetic exfoliants, concrete additives (pozzolan), denim stone-washing, and horticulture as a soil amendment for drainage.
Geological facts
Pumice is the only rock that can float on water due to its incredible porosity. During massive eruptions, 'pumice rafts' can form in the ocean, stretching for miles and carrying marine life to new islands.
Field identification & locations
Identifiable by its extremely light weight and sponge-like, bubbly appearance. Look for it in volcanic regions, particularly near active or dormant explosive volcanoes like those in Italy, Greece, and the Western USA.
