igneous
Pumice (Volcanic Rock)
Vesicular volcanic rock (composed largely of amorphous volcanic glass)
Hardness: 5-6 (but very brittle); Color: Grey, white, or cream; Luster: Dull/Glassy; Structure: Vesicular (pitted with air bubbles); Specific Gravity: Sub-1.0 (floats in water).
- Hardness
- 5-6 (but very brittle)
- Color
- Grey, white, or cream
- Luster
- Dull/Glassy
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Physical properties
Hardness: 5-6 (but very brittle); Color: Grey, white, or cream; Luster: Dull/Glassy; Structure: Vesicular (pitted with air bubbles); Specific Gravity: Sub-1.0 (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 in a solidified glass foam.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants (pumice stones), lightweight concrete additives, and horticultural soil drainage.
Geological facts
Pumice is the only rock that can float on water for long periods when dry. Large accumulations in the ocean are known as 'pumice rafts' and can drift for thousands of miles.
Field identification & locations
Identify by its extremely lightweight feel (low density) and the presence of numerous small holes (vesicles). Found in volcanic regions like the American West, Iceland, and Italy.
