igneous
Vesicular volcanic rock, likely pumice
Pumice (highly vesicular rhyolitic–dacitic volcanic glass; composition commonly rich in quartz and feldspar)
AI-generated identification · may be incorrectLight gray-white, very porous and frothy, with dull to slightly vitreous luster and no visible crystal cleavage; hardness about 5–6, though fragile, and unusually low specific gravity. The specimen’s texture may also resemble weathered scoria or tuff.
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Physical properties
Light gray-white, very porous and frothy, with dull to slightly vitreous luster and no visible crystal cleavage; hardness about 5–6, though fragile, and unusually low specific gravity. The specimen’s texture may also resemble weathered scoria or tuff.
Formation & geological history
Forms when gas-rich, silica-rich lava erupts explosively and quenches rapidly, trapping bubbles in volcanic glass; ages range from recent eruptions to ancient volcanic deposits. Common around explosive volcanic centers.
Uses & applications
Used as an abrasive, lightweight aggregate, horticultural soil additive, concrete/cement additive, and occasionally in decorative specimens. Usually has little jewelry value.
Geological facts
Pumice can float if its connected pore volume is high enough, unlike most rocks. Its pale color generally indicates felsic magma; darker, denser vesicular material is more likely scoria.
Field identification & locations
Identify by abundant irregular holes, very low weight, sharp frothy surfaces, and lack of layering; it may scratch glass but breaks readily. Common in volcanic regions and as beach-transported float.
