igneous
Pumice
Pumicite
Hardness: 5-6 Mohs. Color: light gray, cream, or pale green. Luster: dull to vitreous. Structure: highly vesicular (full of gas bubbles) and glassy. Specific gravity: low (often floats in water).
- Hardness
- 5-6 Mohs
- Color
- light gray, cream, or pale green
- Luster
- dull to vitreous
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Physical properties
Hardness: 5-6 Mohs. Color: light gray, cream, or pale green. Luster: dull to vitreous. Structure: highly vesicular (full of gas bubbles) and glassy. Specific gravity: low (often floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. It cools rapidly, trapping gas bubbles in a glass matrix. Common in subduction zone volcanoes.
Uses & applications
Used in construction (lightweight concrete), cosmetics (exfoliants), household cleaning (scouring stones), and pencil erasers. Also used in horticulture to aerate soil.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. It is essentially frozen volcanic foam.
Field identification & locations
Identify by its extremely lightweight feel and sponge-like appearance. Found in volcanic regions like the Cascades (USA), Italy, and Iceland. Most have a scratchy, abrasive feel.
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