igneous
Pumice
Pumice (a highly vesicular volcanic rock)
Hardness: 5-6 (Mohs scale); Color: Light gray to tan/white; Luster: Dull to silky; Structure: Vesicular (full of tiny air pockets); Specific gravity: 0.25 to 0.75 (floats in water).
- Hardness
- 5-6 (Mohs scale)
- Color
- Light gray to tan/white
- Luster
- Dull to silky
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Light gray to tan/white; Luster: Dull to silky; Structure: Vesicular (full of tiny air pockets); Specific gravity: 0.25 to 0.75 (floats in water).
Formation & geological history
Formed through explosive volcanic eruptions when rock is ejected into the air; rapid cooling and depressurization create bubbles (vesicles) as gases escape. It is usually found in areas with historic volcanic activity.
Uses & applications
Used as an abrasive in polishing, exfoliating skin (pumice stones), construction (lightweight concrete), and as a soil amendment in horticulture.
Geological facts
Pumice is the only rock that will naturally float on water until it becomes waterlogged. Massive rafts of floating pumice have been known to drift for miles in the ocean after eruptions.
Field identification & locations
Identify in the field by its extreme lightness (very low density) and visible holes. It is often found along coastlines or near volcanoes like Mt. St. Helens.
