igneous
Pumice
Pumice (a highly vesicular volcanic rock)
Hardness: 5-6 (but very brittle); Color: white, cream, or light grey; Luster: dull to pearly; Structure: highly vesicular (full of gas bubbles); Specific Gravity: very low (often floats on water); Texture: frothy or glass-like
- Hardness
- 5-6 (but very brittle)
- Color
- white, cream, or light grey
- Luster
- dull to pearly
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Physical properties
Hardness: 5-6 (but very brittle); Color: white, cream, or light grey; Luster: dull to pearly; Structure: highly vesicular (full of gas bubbles); Specific Gravity: very low (often floats on water); Texture: frothy or glass-like
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is violently ejected. The rapid cooling and depressurization cause gases to expand and create a frothy texture before the lava solidifies into glass.
Uses & applications
Used as an abrasive in toothpaste, soaps, and beauty products (pumice stones). Also used in lightweight concrete, filtration systems, and as a horticultural soil amendment.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged. Large eruptions can create 'pumice rafts' in the ocean that can drift for thousands of miles and span miles across.
Field identification & locations
Identify in the field by its sponge-like appearance and by checking if it feels surprisingly light for its size. It is common in areas with silicic volcanism, such as the American Northwest, Italy, and Greece.
