igneous
Pumice
Pumice (Alveolar Rhyolite / Dacite / Andesite)
Hardness: 5-6 Mohs (though very brittle); Color: white, cream, tan, or gray; Luster: Pearly to dull; Structure: Highly vesicular (honeycombed with air bubbles or vesicles); Cleavage: None; Specific Gravity: 0.25 to 0.6 (typically floats in water).
- Hardness
- 5-6 Mohs (though very brittle)
- Color
- white, cream, tan, or gray
- Luster
- Pearly to dull
Identified More igneous →
Explore Pumice in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 Mohs (though very brittle); Color: white, cream, tan, or gray; Luster: Pearly to dull; Structure: Highly vesicular (honeycombed with air bubbles or vesicles); Cleavage: None; Specific Gravity: 0.25 to 0.6 (typically floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected rapidly, cools quickly, and depressurizes, allowing gas bubbles to expand and freeze in place. This creates a frothy glass texture.
Uses & applications
Used as an abrasive in soaps (like Lava soap), beauty treatments (pumice stones for feet), stone-washing denim, lightweight concrete production, and horticultural soil drainage.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of floating pumice can drift across oceans for years after an undersea eruption.
Field identification & locations
Identify in the field by its extreme lightness (it will feel like Styrofoam) and its numerous tiny holes (vesicles). It is commonly found near volcanic sites such as the Cascades in the US or volcanic islands.
