igneous
Pumice
Vesicular volcanic glass
Hardness: 5-6 Mohs. Color: White, cream, or light grey. Luster: Vitreous to dull. Structure: Vesicular (highly porous) and amorphous (glassy). Cleavage: None. Specific gravity: 0.25 to 0.7 (floats in water).
- Hardness
- 5-6 Mohs
- Color
- White, cream, or light grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 5-6 Mohs. Color: White, cream, or light grey. Luster: Vitreous to dull. Structure: Vesicular (highly porous) and amorphous (glassy). Cleavage: None. Specific gravity: 0.25 to 0.7 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when volatile-rich silicic magma cools rapidly, trapping gas bubbles. Ages range from Holocene to millions of years depending on local volcanic activity.
Uses & applications
Used as an abrasive in polishing, exfoliating soaps, and beauty products. In construction, it is used as a lightweight aggregate for concrete and as a landscaping stone. It is also used in stonewashed denim production.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large outbreaks of pumice in the ocean are known as 'pumice rafts' and can travel thousands of miles.
Field identification & locations
Identify in the field by its sponge-like appearance and its incredibly light weight compared to its size. Often found in proximity to volcanic regions like the Ring of Fire or Iceland. If it floats, it is likely pumice.
