igneous
Pumice
Pumice (Vesicular Felsic Igneous Rock)
Hardness: 6 on Mohs scale (due to glass framework); Color: White, grey, yellowish, brown; Luster: Dull to earthy; Crystal structure: Amorphous (volcanic glass); Specific gravity: Less than 1 (it floats on water due to high porosity).
- Hardness
- 6 on Mohs scale (due to glass framework)
- Color
- White, grey, yellowish, brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 on Mohs scale (due to glass framework); Color: White, grey, yellowish, brown; Luster: Dull to earthy; Crystal structure: Amorphous (volcanic glass); Specific gravity: Less than 1 (it floats on water due to high porosity).
Formation & geological history
Formed from explosive volcanic eruptions involving felsic or intermediate magma with high gas content. As the lava is ejected into the atmosphere, rapid pressure release allows gases to exsolve quickly, creating a frothy foam that cools so rapidly crystals do not form.
Uses & applications
Used widely as an abrasive in pumice stones, exfoliating personal care products, lightweight concrete aggregate, horticulture as soil conditioner, and stonewashing denim.
Geological facts
Pumice is one of the only rocks that can float on water. It has been used for millennia for smoothing skin and as a lightweight building material, notably utilized by the Romans in the construction of the Pantheon's dome.
Field identification & locations
Easily identified by its extremely low weight-to-volume ratio, pale color, and vesicular (sponge-like or frothy) texture filled with tiny gas cavities. Found globally near zones of active or recent tectonic subduction and explosive volcanism.
