igneous
Pumice
Pumice (highly vesicular volcanic glass; typically rhyolitic to dacitic composition)
AI-generated identification · may be incorrectVery light gray-white, dull to silky, highly porous, and commonly lightweight enough to float; hardness about 5–6 Mohs, with no true crystal structure and irregular fracture. The apparent smoothness suggests a worn or shaped specimen.
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Physical properties
Very light gray-white, dull to silky, highly porous, and commonly lightweight enough to float; hardness about 5–6 Mohs, with no true crystal structure and irregular fracture. The apparent smoothness suggests a worn or shaped specimen.
Formation & geological history
Forms when gas-rich felsic magma erupts explosively and rapidly cools, trapping bubbles in volcanic glass; ages range from recent eruptions to millions of years. Common around volcanic arcs and calderas.
Uses & applications
Used as an abrasive, exfoliant, lightweight aggregate, concrete additive, horticultural medium, and landscaping stone; attractive pieces are sold as curiosities. This specimen appears low-grade and likely has minimal commercial value.
Geological facts
Pumice is technically a volcanic glass rather than a fully crystalline rock. Its abundant vesicles make it unusually buoyant, although waterlogged or dense pieces may sink.
Field identification & locations
Identify it by its pale color, frothy texture, sharp or porous surfaces, and very low density; distinguish it from white tuff or slag by its natural vesicles and lack of metallic/glassy industrial appearance. Major sources include Italy, Turkey, Greece, Japan, Iceland, and the western United States.
