igneous
Pumice
Pumice (Volcanic Glass)
Hardness: 5-6 (Mohs), Color: Light gray, tan, or cream, Luster: Dull to pearly, Structure: Vesicular (highly porous/holey), Cleavage: None, Specific Gravity: 0.25-1.2 (often floats on water)
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Physical properties
Hardness: 5-6 (Mohs), Color: Light gray, tan, or cream, Luster: Dull to pearly, Structure: Vesicular (highly porous/holey), Cleavage: None, Specific Gravity: 0.25-1.2 (often floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich frothy magma is ejected and cools rapidly, trapping gas bubbles in a glass matrix.
Uses & applications
Used as an abrasive in cosmetics (foot stones), heavy-duty hand soaps, polishing, lightweight concrete aggregate, and horticultural soil amendments.
Geological facts
Pumice is the only rock that can float on water until it becomes waterlogged. Huge 'pumice rafts' can form in the ocean after underwater volcanic eruptions, traveling thousands of miles.
Field identification & locations
Identify by its extremely light weight, abrasive texture, and 'sponge-like' appearance with visible pits (vesicles). Commonly found in volcanic regions like the Cascades (USA), Italy, and Iceland.
