igneous
Pumice
Volcanic Glass / Pumiceous Rhyolite
Hardness: 5-6 (variable), Color: Light gray, tan, to off-white, Luster: Dull to earthy, Structure: Highly vesicular/porous glass, Specific Gravity: <1.0 (floats on water).
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Physical properties
Hardness: 5-6 (variable), Color: Light gray, tan, to off-white, Luster: Dull to earthy, Structure: Highly vesicular/porous glass, Specific Gravity: <1.0 (floats on water).
Formation & geological history
Formed during explosive volcanic eruptions when super-heated, highly pressurized, gas-rich magma is violently ejected and cools extremely rapidly, trapping gas bubbles within a glassy matrix.
Uses & applications
Widely used as an abrasive in soaps, polishes, and pencil erasers, as lightweight aggregate in concrete, for stone-washing denim, and as a cosmetic exfoliant.
Geological facts
Pumice is the only rock that floats on water due to its incredible abundance of trapped gas pockets (vesicles). Massive pumice rafts created by underwater eruptions can drift across oceans for thousands of miles.
Field identification & locations
Easily identified by its extremely low density, sponge-like vesicular texture, and light coloration. Commonly found in volcanic regions, beaches near ocean vents, and volcanic ash deposits.
