igneous
Pumice
Pumice (Amorphous volcanic glass)
Hardness: 5-6 (Mohs), though brittle; Color: white, cream, or light grey; Luster: dull to pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: 0.25 to 0.9 (floats in water).
- Hardness
- 5-6 (Mohs), though brittle
- Color
- white, cream, or light grey
- Luster
- dull to pearly
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Physical properties
Hardness: 5-6 (Mohs), though brittle; Color: white, cream, or light grey; Luster: dull to pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: 0.25 to 0.9 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when pressurized, gas-rich molten rock (magma) is ejected into the air, cools rapidly, and depressurizes, freezing the gas bubbles inside a glass matrix.
Uses & applications
Used as an abrasive in cleaning products, exfoliating stones for personal care (pumice stones), lightweight aggregate in concrete/cinder blocks, and in stonewashing textiles like denim jeans.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. Massive 'pumice rafts' resulting from underwater eruptions have been known to float across oceans for years.
Field identification & locations
Identify in the field by its extreme lightness (low density) and frothy, abrasive texture. Commonly found in volcanic regions such as the Ring of Fire or areas with history of rhyolitic eruptions.
