igneous
Pumice
Pumice (Vitreous volcanic rock)
Hardness: 5-6 (but brittle), Color: Cream/Light Grey, Luster: Dull to Pearly, Structure: Highly vesicular/porous, Density: Often floats on water.
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Physical properties
Hardness: 5-6 (but brittle), Color: Cream/Light Grey, Luster: Dull to Pearly, Structure: Highly vesicular/porous, Density: Often floats on water.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich molten rock (magma) is ejected into the air; it cools quickly, trapping gas bubbles (vesicles).
Uses & applications
Used as an abrasive in polishing, cosmetic exfoliants, lightweight concrete, and as a horticultural soil amendment (perlite alternative).
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large pumice rafts can travel for miles in the ocean after an eruption.
Field identification & locations
Identify by its extremely lightweight feel, light color, and 'sponge-like' texture with tiny holes. Found in volcanic regions like the Cascades or Mediterranean.
