igneous
Pumice
Pumice (Volcanic glass / Silicic extrusive rock)
Hardness: 6 on the Mohs scale; Color: Light gray, white, yellowish, or brownish; Luster: Dull to earthy; Crystal structure: Amorphous (volcanic glass foam with trapped gas bubbles); Cleavage: None; Specific gravity: Less than 1.0 (it floats on water).
- Hardness
- 6 on the Mohs scale
- Color
- Light gray, white, yellowish, or brownish
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on the Mohs scale; Color: Light gray, white, yellowish, or brownish; Luster: Dull to earthy; Crystal structure: Amorphous (volcanic glass foam with trapped gas bubbles); Cleavage: None; Specific gravity: Less than 1.0 (it floats on water).
Formation & geological history
Formed from explosive volcanic eruptions involving high-silica magma containing dissolved gases, which rapidly depressurizes and cools, trapping gas bubbles within the solidifying glass foam.
Uses & applications
Used in lightweight construction materials, concrete aggregate, abrasive agents in soaps, pumice stones for personal care, horticulture as a soil amendment, and filtration.
Geological facts
Pumice is one of the only rocks that can float on water due to its high porosity and trapped air bubbles. Large underwater volcanic eruptions can create massive 'pumice rafts' that drift across oceans for months.
Field identification & locations
Easily identified by its extremely light weight, pale color, abrasive texture, and numerous small holes (vesicles). Found globally near active or historical volcanic regions, particularly subduction zones and areas with rhyolitic volcanism.
