igneous
Pumice
Pumice (a volcanic glass, primarily SiO2)
Hardness: 5-6 (but very brittle); Color: Cream, white, or light gray; Luster: Dull or silky; Structure: Vesicular (highly porous/bushed); Specific Gravity: Extremely low (often floats in water)
- Hardness
- 5-6 (but very brittle)
- Color
- Cream, white, or light gray
- Luster
- Dull or silky
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Physical properties
Hardness: 5-6 (but very brittle); Color: Cream, white, or light gray; Luster: Dull or silky; Structure: Vesicular (highly porous/bushed); Specific Gravity: Extremely low (often 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 as it solidifies.
Uses & applications
Used as an abrasive in polishing, skin exfoliation (pumice stones), heavyweight-reducing concrete aggregate, and in 'stone-washing' denim jeans.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of pumice have been known to float in the ocean for years.
Field identification & locations
Identify by its light weight and 'frothy' appearance full of tiny holes (vesicles). It is commonly found in areas of past or present volcanic activity, such as the Ring of Fire or island arcs.
