igneous
Pumice
Pumice (Vesicular Rhyolite/Andesite)
Hardness: 5-6 (Mohs), Color: Light gray to tan, Luster: Dull to pearly, Texture: Highly vesicular (porous), Density: Very low (often floats on water), Crystal structure: Amorphous/Glassy
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Physical properties
Hardness: 5-6 (Mohs), Color: Light gray to tan, Luster: Dull to pearly, Texture: Highly vesicular (porous), Density: Very low (often floats on water), Crystal structure: Amorphous/Glassy
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock is violently ejected and cools rapidly, trapping gas bubbles (vesicles) as it solidifies.
Uses & applications
Used as an abrasive in cleaning products, skin exfoliants (pumice stones), lightweight concrete aggregate, pencil erasers, and for stone-washing denim.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of floating pumice can travel thousands of miles across oceans after eruptions.
Field identification & locations
Identify by its 'sponge-like' appearance, light weight, and ability to float. Commonly found near active or dormant volcanic regions and along beaches near subduction zones.
