igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 (but brittle); Color: cream, tan, or gray; Luster: dull to pearly; Crystal structure: amorphous/glassy; Cleavage: none; Specific gravity: 0.25 to 0.7 (floats on water)
- Hardness
- 5-6 (but brittle)
- Color
- cream, tan, or gray
- Luster
- dull to pearly
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (but brittle); Color: cream, tan, or gray; Luster: dull to pearly; Crystal structure: amorphous/glassy; Cleavage: none; Specific gravity: 0.25 to 0.7 (floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when pressurized, gas-rich magma is rapidly cooled, creating a highly vesicular (porous) froth of volcanic glass.
Uses & applications
Used in cosmetics as an exfoliant, in abrasive cleaners, as a lightweight aggregate in concrete, and for horticultural soil amendments.
Geological facts
Pumice is the only rock that floats on water. Massive 'pumice rafts' can form after submarine volcanic eruptions and drift for thousands of miles across oceans.
Field identification & locations
Identify by its extremely lightweight feel and high concentration of small holes (vesicles). It is commonly found near volcanic arcs and around active or dormant volcanoes worldwide.
