igneous
Pumice
Pumice (a vesicular volcanic glass)
Hardness: 5-6 (but very brittle); Color: Cream, light gray, or tan; Luster: Dull to silky; Structure: Highly vesicular/cellular; Specific Gravity: Below 1.0 (it floats in water).
- Hardness
- 5-6 (but very brittle)
- Color
- Cream, light gray, or tan
- Luster
- Dull to silky
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Physical properties
Hardness: 5-6 (but very brittle); Color: Cream, light gray, or tan; Luster: Dull to silky; Structure: Highly vesicular/cellular; Specific Gravity: Below 1.0 (it floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected into the air, cooling rapidly and trapping gas bubbles.
Uses & applications
Used as an abrasive in soaps, foot scrubs (pumice stones), and industrial polishing. Also used in lightweight concrete and horticultural soil mixes.
Geological facts
Pumice is the only rock that can float on water due to its high porosity. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify by its light weight and 'frothy' appearance. It is commonly found near volcanic arcs and subduction zones like the Cascades or the Mediterranean.
