igneous
Pumice
Pumice (a highly vesicular volcanic glass)
Hardness: 5-6 (Mohs), but brittle; Color: White, cream, or light gray; Luster: Dull to pearly; Crystal structure: Amorphous (glassy); Cleavage: None; Specific Gravity: less than 1.0 (it floats on water)
- Hardness
- 5-6 (Mohs), but brittle
- Color
- White, cream, or light gray
- Luster
- Dull to pearly
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), but brittle; Color: White, cream, or light gray; Luster: Dull to pearly; Crystal structure: Amorphous (glassy); Cleavage: None; Specific Gravity: less than 1.0 (it floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected into the air; the rapid cooling and depressurization trap gas bubbles in a frothy glass structure. It is found in volcanic regions of any geological age from Holocene to ancient.
Uses & applications
Used as a lightweight aggregate in concrete, as an abrasive in industrial polishing and 'stone-washed' jeans, in horticultural soil mixes to improve aeration, and as a cosmetic exfoliant (pumice stones).
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large rafts of pumice have been known to float in the ocean for years following major volcanic eruptions like Krakatoa.
Field identification & locations
Identify in the field by its extreme lightness (low density) and frothy, sponge-like texture. It is commonly found in volcanic fields such as those in the American West, Italy, Iceland, and New Zealand.
