igneous
Pumice
Pumicite (Amorphous Volcanic Glass)
Hardness: 5-6 (Mohs scale), Color: light gray to cream, Luster: dull to pearly (silky), Structure: highly vesicular (pitted with air bubbles), Specific Gravity: very low (less than 1.0, floats in water).
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Physical properties
Hardness: 5-6 (Mohs scale), Color: light gray to cream, Luster: dull to pearly (silky), Structure: highly vesicular (pitted with air bubbles), Specific Gravity: very low (less than 1.0, floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when magma with high gas and water content is ejected into the air; it cools rapidly (quenching) while gases expand to create a frothy texture.
Uses & applications
Used as an abrasive in polishing and liquid soaps, as a lightweight aggregate for concrete and cinder blocks, in horticulture as a soil conditioner, and for exfoliating skin (pumice stones).
Geological facts
Pumice is the only rock that can float on water due to its trapped air bubbles. Large underwater eruptions can create 'pumice rafts' that drift for thousands of miles across the ocean.
Field identification & locations
Identify by its light-as-air weight and porous 'sponge-like' appearance. Commonly found in volcanic regions such as the Ring of Fire, Mediterranean islands, and the Andes. If it floats in a glass of water, it is almost certainly pumice.
