igneous
Pumice
Pumice (Volcanic Rock / Glass Foam)
Hardness: 6 on the Mohs scale; Color: White, grey, yellowish, or brown; Luster: Dull to earthy; Crystal structure: Amorphous (volcanic glass foam with vesicular texture); Specific gravity: Less than 1.0 (it floats on water).
- Hardness
- 6 on the Mohs scale
- Color
- White, grey, yellowish, or brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on the Mohs scale; Color: White, grey, yellowish, or brown; Luster: Dull to earthy; Crystal structure: Amorphous (volcanic glass foam with vesicular texture); Specific gravity: Less than 1.0 (it floats on water).
Formation & geological history
Formed during explosive volcanic eruptions involving felsic or intermediate magma rich in dissolved gases. As the magma is ejected into the atmosphere, pressure drops rapidly, causing gases to exsolve and form bubbles while the lava cools quickly into a glassy foam.
Uses & applications
Used widely in lightweight construction materials, abrasive soaps, pumice stones for personal care, horticulture as a soil conditioner, and filtration.
Geological facts
Pumice is one of the only rocks that can float on water due to its high porosity and trapped air bubbles. Large amounts can form vast floating rafts after submarine volcanic eruptions.
Field identification & locations
Easily identified by its extremely low density, light color, and frothy, vesicular texture filled with tiny gas cavities. Found worldwide in regions with past or active volcanic activity, particularly in areas associated with subduction zones.
