igneous
Pumice
Volcanic glass / Pumiceous rock
Hardness: 5-6 (Mohs scale), Color: Light grey to off-white or yellowish, Luster: Dull to earthy, Texture: Highly vesicular with many tiny, interconnected gas pores (cavities), Specific Gravity: Very low (often floats on water)
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Light grey to off-white or yellowish, Luster: Dull to earthy, Texture: Highly vesicular with many tiny, interconnected gas pores (cavities), Specific Gravity: Very low (often floats on water)
Formation & geological history
Formed during explosive volcanic eruptions when highly gas-saturated, felsic (silica-rich) magma cools rapidly, trapping expanding gas bubbles inside a porous matrix of volcanic glass.
Uses & applications
Widely used in abrasive cleaners, cosmetics (exfoliants and foot stones), light-weight concrete manufacturing, denim stonewashing, and horticulture for soil drainage.
Geological facts
Pumice is unique among rocks because its density is often less than 1.0 g/cm³, meaning it can float on water until its pores eventually become waterlogged.
Field identification & locations
Identified in the field by its sponge-like, highly vesicular, porous texture and extremely light weight relative to its size. Commonly found near active or ancient explosive volcanic sites, coastal beaches, and river beds carrying volcanic runoff.
