igneous
Pumice
Pumice (Amorphous volcanic glass)
Hardness: 5-6 (Mohs); Color: white, cream, or light grey; Luster: earthy or silky; Crystal structure: Amorphous (glassy); Cleavage: none; Specific gravity: 0.25 to 0.70 (floats on water); Texture: Vesicular (highly porous).
- Hardness
- 5-6 (Mohs)
- Color
- white, cream, or light grey
- Luster
- earthy or silky
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Physical properties
Hardness: 5-6 (Mohs); Color: white, cream, or light grey; Luster: earthy or silky; Crystal structure: Amorphous (glassy); Cleavage: none; Specific gravity: 0.25 to 0.70 (floats on water); Texture: Vesicular (highly porous).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected and cools rapidly, trapping air bubbles inside. Found in volcanic regions worldwide.
Uses & applications
Used as an abrasive in polishing, personal care (exfoliators), lightweight concrete/construction aggregate, and as a horticultural soil amendment.
Geological facts
Pumice is the only rock that consistently floats on water due to its incredible porosity. Massive rafts of pumice have been seen floating in the ocean for miles after submarine eruptions.
Field identification & locations
Identify in the field by its light weight, 'sponge-like' appearance, and ability to float in a puddle or stream. Commonly found near active or dormant volcanic arcs.
