igneous
Pumice
Pumice (Vesicular volcanic glass)
Hardness: 5-6 (though brittle), Color: Light gray to tan, Luster: Dull to pearly/silky, Crystal structure: Amorphous (glassy), Cleavage: None, Specific gravity: 0.25 to 0.7 (floats on water), Texture: Vesicular (highly porous).
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Physical properties
Hardness: 5-6 (though brittle), Color: Light gray to tan, Luster: Dull to pearly/silky, Crystal structure: Amorphous (glassy), Cleavage: None, Specific gravity: 0.25 to 0.7 (floats on water), Texture: Vesicular (highly porous).
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected into the air. The rapid cooling and depressurization cause gas bubbles to be trapped as the rock solidifies quickly into glass.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants (pumice stones), lightweight aggregate in concrete/cinder blocks, and in stonewashed denim production.
Geological facts
Pumice is the only rock that can float on water due to its extreme porosity. Massive rafts of floating pumice can be created by underwater volcano eruptions, sometimes drifting for thousands of miles across oceans.
Field identification & locations
Identify by its extremely lightweight feel and visible holes (vesicles). It is commonly found in volcanic regions such as the Cascades in the USA, Italy, Greece, and Iceland. Collectors should look for unique shapes weathered by water.
