igneous
Pumice
Vesicular volcanic glass, chiefly silica-rich rhyolitic to dacitic composition
AI-generated identification · may be incorrectVery light, highly porous, pale gray to tan, with dull to slightly vitreous luster and no visible crystal structure. Hardness is about 5–6 Mohs; it commonly floats in water because of abundant gas vesicles.
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Physical properties
Very light, highly porous, pale gray to tan, with dull to slightly vitreous luster and no visible crystal structure. Hardness is about 5–6 Mohs; it commonly floats in water because of abundant gas vesicles.
Formation & geological history
Forms when gas-rich volcanic lava erupts explosively and rapidly cools, trapping bubbles in glass. Most specimens are geologically young, commonly Quaternary, though pumice occurs throughout volcanic history.
Uses & applications
Used as an abrasive, exfoliant, lightweight aggregate, cement additive, horticultural medium, and decorative stone; rarely used in jewelry.
Geological facts
Its holes are vesicles created by expanding volcanic gases, not weathering. The specimen’s coarse, open texture is characteristic of pumice rather than dense lava.
Field identification & locations
Identify it by extreme vesicularity, low density, frothy texture, and pale color; it may scratch softer materials and often floats. Common sources include volcanic regions of Italy, Iceland, Japan, Indonesia, New Zealand, Mexico, and the western United States.
