igneous
Pumice
Pumice (Vesicular Volcanic Glass)
Hardness: 5-6 (Mohs scale); Color: Light gray, tan, or white; Luster: Pearly to Vitreous; Crystal structure: Amorphous (non-crystalline glass); Cleavage: None; Specific gravity: 0.25 to 0.7 (floats on water); Texture: Highly vesicular (pitted with tiny holes).
- Hardness
- 5-6 (Mohs scale)
- Color
- Light gray, tan, or white
- Luster
- Pearly to Vitreous
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Light gray, tan, or white; Luster: Pearly to Vitreous; Crystal structure: Amorphous (non-crystalline glass); Cleavage: None; Specific gravity: 0.25 to 0.7 (floats on water); Texture: Highly vesicular (pitted with tiny holes).
Formation & geological history
Formed during explosive volcanic eruptions when gas-rich, frothy magma cools very rapidly, trapping gas bubbles (vesicles) as the rock solidifies. It is primarily associated with felsic magmas rich in silica.
Uses & applications
Used as an abrasive in polishing and personal care (pumice stones), lightweight aggregate in concrete/cinder blocks, a soil amendment in horticulture, and in stone-washing processes for denim.
Geological facts
Pumice is the only rock that consistently floats on water due to its low density and high porosity. Large 'pumice rafts' can form in the ocean after massive underwater volcanic eruptions and can float for miles.
Field identification & locations
Identify in the field by its extreme lightness, porous texture, and ability to float. Commonly found in regions with explosive volcanic history such as Italy, Greece, the Pacific Northwest (USA), and Iceland.
