igneous
Weathered vesicular basalt (possible scoria)
Basalt, predominantly plagioclase and pyroxene with possible olivine; iron-oxide weathering
AI-generated identification · may be incorrectHardness about 6 Mohs; brown-orange weathered surface with gray-black patches, dull to slightly vitreous luster, and abundant rounded vesicles. Fine-grained, massive texture; no obvious cleavage, with moderate density despite the pores.
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Physical properties
Hardness about 6 Mohs; brown-orange weathered surface with gray-black patches, dull to slightly vitreous luster, and abundant rounded vesicles. Fine-grained, massive texture; no obvious cleavage, with moderate density despite the pores.
Formation & geological history
Formed when low-silica lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; the brown coloration reflects oxidation and weathering. Commonly Cenozoic or younger, though basalt occurs throughout geologic time.
Uses & applications
Used as aggregate, roadstone, riprap, and occasionally decorative stone; attractive vesicular pieces are collected but are generally not gemstone material.
Geological facts
The specimen’s strongly rounded, mushroom-like shape is likely from water abrasion or transport rather than its original lava flow form. Dark cavities may contain weathered minerals or sediment.
Field identification & locations
Identify by its dark mafic composition, vesicles, relatively high density, and lack of layering; it commonly occurs in volcanic terrains, riverbeds, beaches, and glacial deposits. A hand lens and streak, hardness, and magnetism tests can help distinguish it from porous sedimentary rock.
