igneous
Pumice
Pumice; vesicular volcanic glass, typically rhyolitic to dacitic in composition
AI-generated identification · may be incorrectLight tan, highly porous, and dull to glassy, with abundant tiny vesicles; hardness about 5–6 Mohs, irregular fracture, no cleavage, and low specific gravity—often able to float. Composition commonly includes silica-rich volcanic glass with feldspar, quartz, and minor dark minerals.
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Physical properties
Light tan, highly porous, and dull to glassy, with abundant tiny vesicles; hardness about 5–6 Mohs, irregular fracture, no cleavage, and low specific gravity—often able to float. Composition commonly includes silica-rich volcanic glass with feldspar, quartz, and minor dark minerals.
Formation & geological history
Forms when gas-rich, silica-rich lava erupts explosively and rapidly cools, trapping bubbles in glass; ages range from recent eruptions to ancient volcanic deposits. Common around volcanic arcs, calderas, and subduction zones.
Uses & applications
Used as an abrasive, lightweight aggregate, concrete additive, horticultural soil amendment, and exfoliating stone; attractive pieces are sold as inexpensive specimens.
Geological facts
Its extreme vesicularity distinguishes it from denser volcanic rocks; it may float until its pores become waterlogged. The specimen appears water-worn and rounded, likely collected from a beach, river, or volcanic shore.
Field identification & locations
Identify by very low density, abundant connected pores, pale color, and rough texture; unlike scoria, pumice is generally lighter-colored and silica-rich. Common in Italy, Greece, Iceland, Japan, New Zealand, and the western United States.
