igneous
Pumice
Vesicular Rhyolite (highly vesicular igneous volcanic rock)
Hardness: 5-6 Mohs (though fragile), Color: light gray to cream, Luster: dull to pearly, Structure: vesicular (highly porous/bubbly), Specific Gravity: 0.25 to 0.7 (floats in water).
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Physical properties
Hardness: 5-6 Mohs (though fragile), Color: light gray to cream, Luster: dull to pearly, Structure: vesicular (highly porous/bubbly), Specific Gravity: 0.25 to 0.7 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (magma) is ejected into the air, cooling rapidly and trapping gas bubbles as it solidifies.
Uses & applications
Used as an abrasive in polishing, pencil erasers, and cosmetic exfoliating stones. Also used in lightweight concrete, horticulture (soil aeration), and 'stone-washed' denim production.
Geological facts
Pumice is the only rock that consistently floats on water due to its air-filled pores. Large volcanic eruptions can create 'pumice rafts' that drift across oceans for thousands of miles.
Field identification & locations
Identify by its extremely light weight relative to its size and its rough, scratchy texture. It is commonly found in areas of recent volcanic activity such as the Andes, Italy, or the American Northwest.
