igneous
Pumice
Pumice (a highly vesicular volcanic glass)
Hardness: 5-6 (Mohs scale), Color: light grey to cream, Luster: dull to pearly, Crystal structure: amorphous (glassy), Cleavage: none, Specific Gravity: 0.25-0.90 (floats on water)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: light grey to cream, Luster: dull to pearly, Crystal structure: amorphous (glassy), Cleavage: none, Specific Gravity: 0.25-0.90 (floats on water)
Formation & geological history
Formed during explosive volcanic eruptions from felsic (silica-rich) lava that cools rapidly while gasses are escaping, creating a frothy, vesicular texture.
Uses & applications
Used as an abrasive in cleaning products, cosmetic exfoliants, lightweight concrete, stone-washing denim, and filtration systems.
Geological facts
Pumice is the only rock that can float on water due to its air-filled vesicles. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify by its light weight, porous sponge-like appearance, and ability to float. Commonly found near active or dormant volcanic regions like the Mediterranean, Andes, or Pacific Northwest.
