igneous
Pumice
Pumice (Highly vesicular volcanic glass)
Hardness: 5-6 Mohs (though fragile due to air pockets); Color: White, cream, gray, or light brown; Luster: Dull to pearly; Structure: Vesicular (full of tiny holes); Specific Gravity: 0.25-0.9 (Floats in water).
- Hardness
- 5-6 Mohs (though fragile due to air pockets)
- Color
- White, cream, gray, or light brown
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 Mohs (though fragile due to air pockets); Color: White, cream, gray, or light brown; Luster: Dull to pearly; Structure: Vesicular (full of tiny holes); Specific Gravity: 0.25-0.9 (Floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly. It has occurred throughout geological history, notably in the Cenozoic era. The gas bubbles are 'frozen' in the rock, creating its unique porous structure.
Uses & applications
Used in construction for lightweight concrete, in personal care as an exfoliant (pumice stones), as an abrasive in industrial polishing, and in horticulture to improve soil drainage.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that float across oceans for thousands of miles.
Field identification & locations
Identify in the field by its extremely light weight and glass-like, porous texture; if it floats in a puddle, it is pumice. Commonly found near convergent plate boundaries and areas with active or dormant volcanoes like Italy, Greece, and the Western USA.
