igneous
Pumice
Vesicular volcanic glass, composition commonly rhyolitic to dacitic (SiO₂-rich)
AI-generated identification · may be incorrectVery light, porous, pale gray-white, and dull to slightly vitreous; hardness about 5–6 Mohs, with abundant vesicles and no cleavage. It may float if its pores are sufficiently open.
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Physical properties
Very light, porous, pale gray-white, and dull to slightly vitreous; hardness about 5–6 Mohs, with abundant vesicles and no cleavage. It may float if its pores are sufficiently open.
Formation & geological history
Forms when gas-rich, silica-rich lava erupts explosively and rapidly quenches, trapping bubbles in volcanic glass; typically Quaternary to modern, though older deposits are widespread.
Uses & applications
Used as an abrasive, lightweight aggregate, concrete additive, horticultural medium, and exfoliating material; attractive pieces are sold as inexpensive specimens.
Geological facts
Its many vesicles distinguish it from dense volcanic rocks; pumice can be abrasive enough to remove calluses and polish surfaces.
Field identification & locations
Identify by its extreme lightness, frothy texture, sharp porous surfaces, and pale color. Common around explosive volcanoes, including Italy, Iceland, Japan, Indonesia, Greece, and the western United States.
