igneous
Pumice
Pumice (a highly vesicular volcanic glass)
Hardness: 5-6 Mohs scale; Color: typically light gray, cream, or light brown; Luster: vitreous to dull; Crystal structure: Amorphous (glassy); Cleavage: none; Specific gravity: 0.25 to 0.7 (extremely low, often floats in water).
- Hardness
- 5-6 Mohs scale
- Color
- typically light gray, cream, or light brown
- Luster
- vitreous 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 scale; Color: typically light gray, cream, or light brown; Luster: vitreous to dull; Crystal structure: Amorphous (glassy); Cleavage: none; Specific gravity: 0.25 to 0.7 (extremely low, often floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly. The trapped gas bubbles expand as the pressure drops, creating the porous, frothy texture.
Uses & applications
Used as an abrasive in cosmetics (exfoliation), cleaning supplies, and stonewashing jeans. It is also used as lightweight aggregate in concrete and as a soil amendment in horticulture.
Geological facts
Pumice is the only rock that can float on water until it eventually becomes waterlogged. Large 'pumice rafts' have been observed in the ocean following underwater volcanic eruptions.
Field identification & locations
Identify by its extremely lightweight feel and frothy, 'sponge-like' appearance full of tiny holes (vesicles). Found in volcanic regions worldwide including Cascade Range, Andes, and Mediterranean.
