igneous
Pumice
Pumice (Vesicular intermediate to felsic volcanic glass)
Hardness: 6 (Mohs), Color: light gray to yellowish-tan, Luster: dull to pearly, Crystal structure: amorphous (glassy), Cleavage: none, Specific gravity: 0.25 to 0.7 (extremely buoyant)
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Physical properties
Hardness: 6 (Mohs), Color: light gray to yellowish-tan, Luster: dull to pearly, Crystal structure: amorphous (glassy), Cleavage: none, Specific gravity: 0.25 to 0.7 (extremely buoyant)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected and cools rapidly, trapping air bubbles (vesicles). Primarily of Cenozoic to recent geological age.
Uses & applications
Used as an abrasive in soaps and cleaners, in horticultural soil mixes, as a lightweight aggregate in concrete, and for skin exfoliation products.
Geological facts
Pumice is the only rock that can float on water due to its low density and high gas content. After major eruptions, floating pumice rafts can drift on the ocean for years.
Field identification & locations
Identified by its extremely light weight, frothy texture, and numerous small holes (vesicles). Found in volcanic regions like the Cascades, Italy, and Iceland. If it floats in water, it is almost certainly pumice.
