igneous
Pumice
Volcanic pumice; chiefly vesicular volcanic glass composed of rhyolitic to dacitic silicates
AI-generated identification · may be incorrectVery light gray, highly porous, rough, and dull to silky; hardness about 5–6 Mohs, no cleavage, and commonly floats in water. The visible abundant vesicles indicate gas-rich volcanic glass rather than a crystalline rock.
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Physical properties
Very light gray, highly porous, rough, and dull to silky; hardness about 5–6 Mohs, no cleavage, and commonly floats in water. The visible abundant vesicles indicate gas-rich volcanic glass rather than a crystalline rock.
Formation & geological history
Forms when frothy, silica-rich lava erupts explosively and quenches rapidly, trapping expanding gas bubbles; specimens are generally geologically young, ranging from recent eruptions to older Cenozoic deposits.
Uses & applications
Used as an abrasive, exfoliating stone, lightweight aggregate, concrete additive, horticultural soil amendment, and in polishing products; attractive pieces may be collected but are rarely used as gemstones.
Geological facts
Pumice can float until its pores fill with water. Its density and texture vary widely, and darker basaltic pumice is called scoria when it is more crystalline and iron-rich.
Field identification & locations
Identify by its extremely low density, abundant interconnected holes, sharp rough texture, and lack of visible mineral grains; common around explosive volcanic regions such as Italy, Iceland, Japan, the western United States, and the Pacific Rim.
