igneous
Pumice
Pumice (a highly vesicular volcanic rock)
Hardness: 5-6 (Mohs), Color: Light gray to white/cream, Luster: Dull or silky, Structure: Highly vesicular/porous, Density: Usually floats on water.
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Physical properties
Hardness: 5-6 (Mohs), Color: Light gray to white/cream, Luster: Dull or silky, Structure: Highly vesicular/porous, Density: Usually floats on water.
Formation & geological history
Formed during explosive volcanic eruptions from cooling silica-rich lava (rhyolite or dacite). Rapid cooling and depressurization trap gas bubbles, creating a frothy texture.
Uses & applications
Used as an abrasive in cosmetics (exfoliants), polishing stones, construction (lightweight concrete), filtration, and stone-washing blue jeans.
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 drift for years.
Field identification & locations
Identify by its extremely lightweight feel, light color, and the presence of numerous tiny holes (vesicles). It is commonly found near volcanic sites such as those in Italy, Greece, and the Western United States.
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