igneous
Dark gray rounded stone, possibly basalt or slag
Uncertain; likely fine-grained basalt (plagioclase–pyroxene) or iron-rich industrial slag
AI-generated identification · may be incorrectSmall, rounded, dark gray-black specimen with dull to weakly vitreous luster and an apparent vesicle or indentation. Estimated Mohs hardness 5–6 if basalt; crystal grains are too small to resolve, and cleavage is absent; density is typically 2.8–3.2 g/cm³.
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Physical properties
Small, rounded, dark gray-black specimen with dull to weakly vitreous luster and an apparent vesicle or indentation. Estimated Mohs hardness 5–6 if basalt; crystal grains are too small to resolve, and cleavage is absent; density is typically 2.8–3.2 g/cm³.
Formation & geological history
If basalt, it formed when mafic lava rapidly cooled, commonly during the Cenozoic or older volcanic episodes; if slag, it is human-made and not geological. The image alone cannot distinguish these possibilities.
Uses & applications
Basalt is used as aggregate, road stone, and occasionally decorative stone; small pieces have little commercial value. Slag may be collected as an industrial artifact but is generally not valuable.
Geological facts
Basalt commonly attracts weakly to moderately if it contains magnetite, while slag may be strongly magnetic, unusually vesicular, or show glassy flow textures.
Field identification & locations
Inspect for interlocking fine grains, natural weathering, and consistent density; a magnet, streak test, and close view of broken surfaces would help. Common basalt localities include volcanic regions worldwide.
