igneous
Pumice
Pumice (Volcanic Glass)
Hardness: 6 on the Mohs scale; Color: White, grey, yellowish, or brown; Luster: Earthy to silky; Crystal structure: Amorphous (volcanic glass); Cleavage: None; Specific gravity: Less than 1.0 (it floats on water due to high porosity)
- Hardness
- 6 on the Mohs scale
- Color
- White, grey, yellowish, or brown
- Luster
- Earthy to silky
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Physical properties
Hardness: 6 on the Mohs scale; Color: White, grey, yellowish, or brown; Luster: Earthy to silky; Crystal structure: Amorphous (volcanic glass); Cleavage: None; Specific gravity: Less than 1.0 (it floats on water due to high porosity)
Formation & geological history
Formed from explosive volcanic eruptions where gas-rich felsic lava cools rapidly, causing gases to exsolve and form bubbles that are trapped as the lava solidifies into a frothy glass foam.
Uses & applications
Used in lightweight construction aggregates, concrete, abrasive soaps, exfoliating cosmetics, horticulture as a soil amendment, and stonewashing jeans.
Geological facts
Pumice is one of the very few rocks that can float on water due to its extremely high vesicularity. It is also used in polishing compounds and has been utilized since Roman times in construction and hygiene.
Field identification & locations
Easily identified by its extremely light weight, pale color, abrasive texture, and numerous tiny gas cavities (vesicles). Found worldwide near regions of recent volcanic activity, particularly in areas with silica-rich lavas such as the Mediterranean, USA, and New Zealand.
