igneous
Pumice
Pumicite (Amorphous Volcanic Glass)
Hardness: 5-6 (Mohs), though brittle; Color: white, cream, tan, or grey; Luster: vitreous to pearly (silky); Structure: highly vesicular (full of gas bubbles); Cleavage: none; Specific Gravity: 0.25 to 0.7 (floats in water).
- Hardness
- 5-6 (Mohs), though brittle
- Color
- white, cream, tan, or grey
- Luster
- vitreous to pearly (silky)
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 brittle; Color: white, cream, tan, or grey; Luster: vitreous to pearly (silky); Structure: highly vesicular (full of gas bubbles); Cleavage: none; Specific Gravity: 0.25 to 0.7 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when high-pressure, gas-rich magma is ejected and cools rapidly, trapping gas bubbles. Often found in pyroclastic deposits from the Cenozoic era to the present.
Uses & applications
Used as an abrasive in hand soaps (Lava soap), exfoliating stones, and dental polishing. Also used in light-weight concrete, horticultural soil amendments, and stonewashing denim jeans.
Geological facts
Pumice is the only rock that can float on water due to its low density and air-filled pores. Large eruptions can create 'pumice rafts' in the ocean that travel for thousands of miles.
Field identification & locations
Identify in the field by its light weight (it should feel lighter than it looks) and its vesicular, sponge-like texture. Common in volcanic regions like the Cascades, Italy, or Iceland. If it's very light and floats, it's pumice.
