igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 Mohs (though brittle); Color: Light gray to cream; Luster: Dull to pearly/silky; Crystal structure: Amorphous (glassy); Cleavage: None; Specific gravity: 0.25 to 0.7 (floats on water); Vesicular texture with many air holes.
- Hardness
- 5-6 Mohs (though brittle)
- Color
- Light gray to cream
- Luster
- Dull to pearly/silky
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Physical properties
Hardness: 5-6 Mohs (though brittle); Color: Light gray to cream; Luster: Dull to pearly/silky; Crystal structure: Amorphous (glassy); Cleavage: None; Specific gravity: 0.25 to 0.7 (floats on water); Vesicular texture with many air holes.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles in a glass-like matrix.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants, masonry/concrete lightweight aggregate, and in denim stone-washing.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. Massive pumice 'rafts' stretching for miles have been observed in the ocean after underwater volcanic eruptions.
Field identification & locations
Identify by its extremely lightweight feel and vesicular (sponge-like) appearance. Commonly found near explosive volcanic regions like the Andes, Cascade Range, and Mediterranean.
