igneous
Weathered vesicular volcanic rock (likely pumice or altered basalt)
Vesicular basalt–pumice, compositionally uncertain
AI-generated identification · may be incorrectLight gray to tan, highly porous, dull to weakly earthy luster, with abundant irregular vesicles and no visible crystal faces. Likely hardness about 5–6 if basaltic, or 5–6 for pumice; specific gravity is reduced by vesicles, commonly about 1–2.5.
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Physical properties
Light gray to tan, highly porous, dull to weakly earthy luster, with abundant irregular vesicles and no visible crystal faces. Likely hardness about 5–6 if basaltic, or 5–6 for pumice; specific gravity is reduced by vesicles, commonly about 1–2.5.
Formation & geological history
Formed when gas-rich volcanic lava cooled rapidly, trapping bubbles; later weathering or hydrothermal alteration produced the pale, friable surface. Its exact geological age cannot be determined from the photograph.
Uses & applications
Pumice is used as an abrasive, lightweight aggregate, horticultural medium, and in concrete; basalt is used for crushed stone and construction aggregate. This weathered specimen has little commercial value.
Geological facts
The key diagnostic feature is vesicular texture—holes formed by expanding volcanic gases—not fossil structure. A streak, density test, and examination of a fresh broken surface would help distinguish pumice from altered basalt or volcanic tuff.
Field identification & locations
Common near volcanic fields, lava flows, cinder cones, and beaches receiving volcanic debris. It may float if pumice is sufficiently porous; basaltic material usually sinks and feels noticeably denser.
