igneous
Pumice (with oxidation)
Pumice (Vitreous pyroclastic rock)
Hardness: 5-6 (Mohs scale); Color: Light gray with reddish-brown oxidation spots; Luster: Dull to pearly; Crystal structure: Amorphous/Vitreous (volcanic glass); Specific gravity: 0.25 to 0.7 (often floats on water).
- Hardness
- 5-6 (Mohs scale)
- Color
- Light gray with reddish-brown oxidation spots
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Light gray with reddish-brown oxidation spots; Luster: Dull to pearly; Crystal structure: Amorphous/Vitreous (volcanic glass); Specific gravity: 0.25 to 0.7 (often floats on water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles in a frothy glass matrix. Usually Holocene to Pleistocene in age.
Uses & applications
Used as an abrasive in cleaning and personal care (pumice stones), lightweight aggregate in concrete, horticultural soil amendment, and in stone-washing textiles.
Geological facts
Pumice is the only rock that can float on water due to its high porosity. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify by its extremely lightweight feel, highly vesicular (hole-filled) texture, and rough/abrasive surface. Common in volcanic regions like the Cascades, Andes, and Mediterranean.
