igneous
Pumice
Pumiceous rhyolite
Hardness: 5-6 Mohs. Color: light gray to whitish. Luster: vitreous to dull. Crystal structure: amorphous/vesicular. Specific gravity: <1.0 (floats on water).
- Hardness
- 5-6 Mohs
- Color
- light gray to whitish
- Luster
- vitreous to dull
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Physical properties
Hardness: 5-6 Mohs. Color: light gray to whitish. Luster: vitreous to dull. Crystal structure: amorphous/vesicular. Specific gravity: <1.0 (floats on water).
Formation & geological history
Extrusive volcanic rock formed when highly pressurized lava is violently ejected from a volcano, cooling rapidly while gas bubbles are trapped inside.
Uses & applications
Used as an abrasive in polishing, skin exfoliation (pumice stones), lightweight aggregate in concrete, and in horticulture for soil aeration.
Geological facts
Pumice is the only rock that can float on water due to its high porosity. Large 'pumice rafts' can form in the ocean after major submarine eruptions.
Field identification & locations
Identify by its incredibly light weight, frothy 'sponge-like' appearance, and ability to float. Commonly found near active or dormant volcanic regions.
