igneous
Pumice
Pumice (volcanic glass)
Hardness: 5-6 (Mohs scale), Color: light gray to creamy white, Luster: dull to vitreous, Structure: highly vesicular (pitted with gas bubbles), specific gravity: 0.25 to 0.7 (floats on water)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: light gray to creamy white, Luster: dull to vitreous, Structure: highly vesicular (pitted with gas bubbles), specific gravity: 0.25 to 0.7 (floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles, creating a frothy glass.
Uses & applications
Used as an abrasive in industrial cleaning, exfoliating stones for personal care, a lightweight aggregate in concrete, and as a soil amendment in horticulture.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. Large pumice rafts can drift across oceans for years after an eruption.
Field identification & locations
Identify by its extremely light weight and porous, sponge-like surface. It is commonly found in volcanic regions such as Italy, Turkey, Greece, and the Western United States.
