igneous
Pumice
Highly vesicular volcanic glass, mainly rhyolitic to dacitic; composition dominated by silica-rich silicate minerals
AI-generated identification · may be incorrectVery light, pale gray, porous, and rough with a dull to slightly glassy luster; typically hardness 5–6 on the Mohs scale, no cleavage, and abundant vesicles. Its low density may allow it to float.
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Physical properties
Very light, pale gray, porous, and rough with a dull to slightly glassy luster; typically hardness 5–6 on the Mohs scale, no cleavage, and abundant vesicles. Its low density may allow it to float.
Formation & geological history
Forms when gas-rich, silica-rich lava erupts explosively and rapidly cools, trapping bubbles in volcanic glass; generally Quaternary to recent, though older examples occur. Common around stratovolcanoes and explosive calderas.
Uses & applications
Used as an abrasive, exfoliating stone, lightweight aggregate, concrete additive, horticultural medium, and industrial polishing material; attractive pieces may be collected but are rarely used as gemstones.
Geological facts
The specimen’s highly porous texture and pale volcanic appearance are consistent with pumice, though weathered scoria or tuff is possible from an image alone.
Field identification & locations
Identify by extreme lightness, frothy cavities, sharp irregular fracture, and lack of visible large crystals; common in volcanic regions worldwide, including Italy, Iceland, Japan, Indonesia, Mexico, and the western United States.
