igneous
Possible basalt or iron-rich river pebble
Fine-grained mafic rock, likely basalt (plagioclase–pyroxene ± olivine, with iron oxides)
AI-generated identification · may be incorrectDark gray to brown, rounded and wet-looking, with dull to weakly vitreous luster; likely hardness about 5–6 Mohs, massive texture, no visible cleavage, and specific gravity roughly 2.8–3.2. The small golden-brown patches may be weathered iron minerals or altered olivine.
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Physical properties
Dark gray to brown, rounded and wet-looking, with dull to weakly vitreous luster; likely hardness about 5–6 Mohs, massive texture, no visible cleavage, and specific gravity roughly 2.8–3.2. The small golden-brown patches may be weathered iron minerals or altered olivine.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust; its age cannot be determined from the image. The rounded shape indicates transport and abrasion in a river, beach, or gravel deposit.
Uses & applications
Ordinary basalt is used as crushed aggregate, road stone, riprap, and occasionally dimension stone; this pebble has little commercial value unless testing reveals an unusual mineral or meteorite origin.
Geological facts
Its appearance can superficially resemble a stony meteorite, but the rounded form, apparent vesicle-free basaltic texture, and rusty patches favor terrestrial basalt. A magnet test may show attraction from magnetite, though this is not diagnostic.
Field identification & locations
Look for a fine-grained dark matrix, small crystals, magnetic response, and a streak that is generally gray rather than metallic; a fresh broken surface is more diagnostic than the wet exterior. Common in volcanic regions and stream gravels.
