igneous
Pumice
Pumice (Felsic volcanic rock)
Mohs hardness: 5-6, Color: White, cream, or grey, Luster: Dull/Glassy, Crystal structure: Amorphous/Vesicular, Specific gravity: <1 (floats on water), Cleavage: None.
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Physical properties
Mohs hardness: 5-6, Color: White, cream, or grey, Luster: Dull/Glassy, Crystal structure: Amorphous/Vesicular, Specific gravity: <1 (floats on water), Cleavage: None.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich silicate magma is ejected and cools rapidly, trapping gas bubbles.
Uses & applications
Used as an abrasive in soaps, foot stones, and denim stone-washing; lightweight aggregate in concrete; and horticultural soil amendment.
Geological facts
Pumice is the only rock that can float on water due to its high porosity. It is essentially frozen volcanic foam.
Field identification & locations
Identify by its extremely lightweight feel, porous (sponge-like) texture, and ability to float. Commonly found in areas with active or historical volcanic activity.
