igneous
Pumice
Pumice (SiO2 + Al2O3 + Fe2O3)
Hardness: 5-6 Mohs. Color: Light grey, cream, or white. Luster: Dull to pearly. Structure: Highly vesicular (porous/bubbly) volcanic glass. Specific Gravity: 0.25-0.9 (floats in water).
- Hardness
- 5-6 Mohs
- Color
- Light grey, cream, or white
- Luster
- Dull to pearly
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Physical properties
Hardness: 5-6 Mohs. Color: Light grey, cream, or white. Luster: Dull to pearly. Structure: Highly vesicular (porous/bubbly) volcanic glass. Specific Gravity: 0.25-0.9 (floats in water).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly, trapping gas bubbles in a solid glass matrix. Found in regions with recent volcanic activity.
Uses & applications
Abrasives (pumice stones), lightweight concrete additive, horticulture (soil aeration), filtration, and cosmetics (exfoliation).
Geological facts
Pumice is the only rock that can reliably float on water until it becomes waterlogged. Huge 'pumice rafts' thousands of miles long have been observed floating in the ocean after underwater volcanic eruptions.
Field identification & locations
Identify by its extremely lightweight feel and visible holes (vesicles). It is abrasive to the touch and usually found near volcanoes or on beaches where it has washed ashore.
