igneous
Pumice
Pumiceous volcanic glass
Hardness: 5-6 (but very brittle), Color: Light gray to tan, Luster: Dull to pearly, Structure: Highly vesicular/frothy, Specific Gravity: 0.25-0.9 (floats in water)
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Physical properties
Hardness: 5-6 (but very brittle), Color: Light gray to tan, Luster: Dull to pearly, Structure: Highly vesicular/frothy, Specific Gravity: 0.25-0.9 (floats in water)
Formation & geological history
Formed during explosive volcanic eruptions when highly pressurized, gas-rich lava is ejected and cools rapidly, trapping bubbles of escaping gas.
Uses & applications
Used as an abrasive in soaps (Lava soap), exfoliating stones, dental polish, and as a lightweight aggregate in concrete and cinder blocks.
Geological facts
Pumice is the only rock that can float on water due to its air-filled pores. Large eruptions can create 'pumice rafts' that drift across oceans for years.
Field identification & locations
Identify by its extremely light weight and porous 'sponge-like' texture. Commonly found in volcanic regions like the Cascades or Mediterranean.
