igneous
Pumice
Pumice (volcanic glass)
Hardness: 5-6 Mohs; Color: White, light gray, or cream; Luster: Dull to pearly; Crystal structure: Amorphous (glassy); Specific gravity: 0.25-0.9 (floats in water); Highly vesicular texture.
- Hardness
- 5-6 Mohs
- Color
- White, light gray, or cream
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 Mohs; Color: White, light gray, or cream; Luster: Dull to pearly; Crystal structure: Amorphous (glassy); Specific gravity: 0.25-0.9 (floats in water); Highly vesicular texture.
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization create bubbles (vesicles), resulting in a frothy volcanic glass.
Uses & applications
Used as an abrasive in cleaning supplies, beauty products (exfoliation), light-weight concrete aggregate, and hydroponics.
Geological facts
Pumice is the only rock that can float on water due to its trapped gas bubbles. After massive eruptions, 'pumice rafts' can float on the ocean for years.
Field identification & locations
Identify by its extremely light weight and porous 'sponge-like' appearance. Commonly found in volcanic regions such as the Cascades, Italy, or Iceland.
