igneous
Pumice
Pumice (Volcanic glass / Felsic igneous rock)
Hardness: 6 on the Mohs scale (due to sharp glass walls), Color: White, yellowish, grey, or light brown, Luster: Dull to silky, Crystal structure: Amorphous (volcanic glass with vesicular texture), Specific gravity: Very low (<1.0, floats on water)
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Physical properties
Hardness: 6 on the Mohs scale (due to sharp glass walls), Color: White, yellowish, grey, or light brown, Luster: Dull to silky, Crystal structure: Amorphous (volcanic glass with vesicular texture), Specific gravity: Very low (<1.0, floats on water)
Formation & geological history
Formed by explosive volcanic eruptions involving felsic or intermediate magma rich in dissolved gases. As pressure drops rapidly during eruption, gases escape, creating a frothy, highly vesicular matrix that rapidly quenches into volcanic glass.
Uses & applications
Used in lightweight concrete, landscaping, abrasive soaps, personal care (pumice stones for exfoliating skin), and industrial abrasives.
Geological facts
Pumice is the only rock known to float on water due to its trapped air bubbles. Large amounts of pumice are often associated with submarine volcanic eruptions, forming floating rafts of rock that can drift across oceans for months.
Field identification & locations
Easily identified in the field by its extreme lightness, vesicular (sponge-like) texture, pale color, and ability to float on water. Found globally around volcanic regions, notably in the Mediterranean, United States, and New Zealand.
