igneous
Pumice
Pumice (a vesicular volcanic glass)
Hardness: 6 (Mohs), Color: White, cream, or light grey, Luster: Dull or pearly, Crystal structure: Amorphous/Vitreous (non-crystalline glass), Cleavage: None, Specific Gravity: 0.25 to 0.90 (floats in water)
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Physical properties
Hardness: 6 (Mohs), Color: White, cream, or light grey, Luster: Dull or pearly, Crystal structure: Amorphous/Vitreous (non-crystalline glass), Cleavage: None, Specific Gravity: 0.25 to 0.90 (floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when pressurized gas-rich silica-rich lava cools so rapidly that gas bubbles are trapped within the solidifying rock, creating a frothy, vesicular texture.
Uses & applications
Used as an abrasive in polishing compounds, stone-washing textiles like jeans, as a lightweight aggregate in concrete/cinder blocks, and in personal care products like exfoliating stones and toothpaste.
Geological facts
Pumice is the only rock that floats on water due to its air-filled pores. It is basically a solidified foam of volcanic glass. Massive rafts of floating pumice have been known to float in the ocean for years after major eruptions.
Field identification & locations
Identify in the field by its extremely light weight, frothy appearance, and ability to float in water. Commonly found near silica-rich volcanic sites in Italy, Greece, Iceland, and the Western USA.
