igneous
Pumice
Vesicular volcanic glass; primarily rhyolitic to dacitic composition, rich in silica (SiO₂)
AI-generated identification · may be incorrectVery light, pale cream to gray, highly vesicular, dull to silky luster, and no visible crystal structure; hardness about 5–6 Mohs, generally too porous for meaningful cleavage, and unusually low density—often capable of floating.
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Physical properties
Very light, pale cream to gray, highly vesicular, dull to silky luster, and no visible crystal structure; hardness about 5–6 Mohs, generally too porous for meaningful cleavage, and unusually low density—often capable of floating.
Formation & geological history
Forms when gas-rich, silica-rich lava explosively decompresses and quenches into frothy volcanic glass; it can form during eruptions of any age, from recent deposits to ancient volcanic terrains.
Uses & applications
Used as an abrasive, exfoliant, lightweight aggregate, horticultural soil additive, and cement/concrete component; attractive pieces are collected but are rarely valuable.
Geological facts
The rounded shape indicates water or sediment transport and surface abrasion. Its pores were created by trapped volcanic gases, not by weathering.
Field identification & locations
Identify it by its lightweight, rough frothy texture, abundant cavities, and ability to scratch softer materials; common at volcanic islands, beaches, and around explosive volcanoes worldwide. The pictured specimen could also be porous scoria or weathered tuff, but its pale color favors pumice.
