igneous
Vesicular basalt (scoria-like volcanic rock)
Vesicular basalt; chiefly plagioclase, pyroxene, and olivine with gas cavities
AI-generated identification · may be incorrectDark brown to black, highly vesicular, dull to weakly vitreous, with a fine-grained mafic groundmass; hardness about 5–6 Mohs and no obvious cleavage. Its low apparent density results from abundant rounded pores, though this specimen appears relatively dense.
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Physical properties
Dark brown to black, highly vesicular, dull to weakly vitreous, with a fine-grained mafic groundmass; hardness about 5–6 Mohs and no obvious cleavage. Its low apparent density results from abundant rounded pores, though this specimen appears relatively dense.
Formation & geological history
Formed when gas-rich basaltic lava cooled rapidly at or near the surface, trapping bubbles; commonly associated with Cenozoic volcanic eruptions, though exact age cannot be determined from the image.
Uses & applications
Used as lightweight aggregate, landscaping stone, abrasives, and occasionally in filtration or horticultural media; generally not used as a gemstone.
Geological facts
The holes are vesicles formed by expanding volcanic gases, and their size and abundance reflect lava viscosity and eruption conditions. Brown coloration commonly results from oxidation of iron-bearing minerals.
Field identification & locations
Common in volcanic regions such as Hawaii, Iceland, the western United States, Italy, and Japan. Distinguish it from industrial slag by its natural, irregular vesicles and crystalline texture; slag may show glassy surfaces or metal-rich inclusions.
