Igneous
Pumice
Pumicite (Amorphous Volcanic Glass)
Hardness: 5-5.5 (though brittle); Color: White, light gray, or cream; Luster: Dull to pearly; Structure: Vesicular (highly porous/bubbly); Specific Gravity: 0.25-1.2 (low enough to float on water initially).
- Hardness
- 5-5
- Color
- White, light gray, or cream
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-5.5 (though brittle); Color: White, light gray, or cream; Luster: Dull to pearly; Structure: Vesicular (highly porous/bubbly); Specific Gravity: 0.25-1.2 (low enough to float on water initially).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected into the air. The rapid cooling and depressurization trap gas bubbles in the solidifying glass. Found in volcanic regions worldwide.
Uses & applications
Used as an abrasive in polishing, skin exfoliation (pumice stones), heavyweight concrete additives, horticultural soil amendments for drainage, and in the production of stone-washed jeans.
Geological facts
Pumice is the only rock known to float on water for extended periods. Large eruptions can create 'pumice rafts' in the ocean that are hundreds of miles long and can float for years.
Field identification & locations
Identify by its extremely lightweight feel and visible holes (vesicles). It is commonly found in areas such as the Ring of Fire or the Mediterranean. Collectors should look for unique glass-string textures.
