igneous
Pumice
Vesicular volcanic glass, commonly rhyolitic to dacitic in composition
AI-generated identification · may be incorrectVery lightweight, pale gray-white, highly porous, dull to weakly vitreous luster, and typically lacking visible crystals; hardness about 5–6 Mohs, with irregular fracture and low specific gravity, often floating in water.
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Physical properties
Very lightweight, pale gray-white, highly porous, dull to weakly vitreous luster, and typically lacking visible crystals; hardness about 5–6 Mohs, with irregular fracture and low specific gravity, often floating in water.
Formation & geological history
Forms when gas-rich lava explosively decompresses and quenches, trapping abundant bubbles in volcanic glass. It can range from geologically young beach-fallout material to specimens millions of years old.
Uses & applications
Used as an abrasive, exfoliant, lightweight aggregate, concrete additive, horticultural medium, and filtration material; small natural pieces are inexpensive collectibles.
Geological facts
The vesicles are frozen gas bubbles, producing its exceptionally low density. The specimen appears consistent with pumice, though a photograph cannot exclude porous scoria or weathered volcanic tuff.
Field identification & locations
Identify it by extreme lightness, abundant interconnected holes, pale color, and scratchability relative to glass; pumice is common near volcanic islands, beaches, and ash deposits worldwide, including the Mediterranean, Japan, Indonesia, and the Pacific Northwest.
