igneous
Pumice
Vesicular Rhyolite or Trachyte (High-silica volcanic glass)
Porous, vesicular texture; color ranges from white/cream to light pink or grey; hardness 5.0-6.0 Mohs; very low density, often floats in water; dull to vitrous luster.
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Physical properties
Porous, vesicular texture; color ranges from white/cream to light pink or grey; hardness 5.0-6.0 Mohs; very low density, often floats in water; dull to vitrous luster.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock is rapidly ejected and cools quickly, trapping gas bubbles (vesicles) in a glass matrix.
Uses & applications
Used as an abrasive in polishing, exfoliating stones (pumice stones), lightweight aggregate in concrete (pumicite), and to produce 'stone-washed' jeans.
Geological facts
Pumice is the only rock that can reliably float on water for long periods due to its high porosity; large floating islands of pumice called 'pumice rafts' can form after submarine eruptions and drift for miles.
Field identification & locations
Identify by its incredibly light weight and sponge-like appearance with many tiny holes. It can be found in volcanic regions or washed up on beaches worldwide.
