igneous
Dark, weathered stone—possibly basalt or slag
Indeterminate; likely fine-grained basalt (plagioclase–pyroxene)
AI-generated identification · may be incorrectDark gray-brown, dull to weakly glassy surface with apparent vesicles or weathering pits; hardness likely about 5–6, no visible cleavage, and fine-grained texture. The image is out of focus, so mineral identification and density cannot be confirmed.
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Physical properties
Dark gray-brown, dull to weakly glassy surface with apparent vesicles or weathering pits; hardness likely about 5–6, no visible cleavage, and fine-grained texture. The image is out of focus, so mineral identification and density cannot be confirmed.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly during Cenozoic volcanism or older oceanic crust formation. If it is industrial slag, it is human-made rather than a natural rock; the rounded, dark appearance alone is insufficient to distinguish them.
Uses & applications
Basalt is used as aggregate, roadstone, riprap, and occasionally as a decorative stone; ordinary pieces have little commercial value. Slag may be used as aggregate but is generally not collectible.
Geological facts
Fresh basalt is typically black to dark gray and may show tiny crystals or gas bubbles; a streak test, magnetism test, and fresh broken surface would help. A sharp image of the specimen and scale would substantially improve identification.
Field identification & locations
Common basalt occurs in volcanic regions and as cobbles in glacial or river deposits worldwide. Estimated value: $0–$5 for a common hand specimen; $5–$20 if unusually vesicular, polished, or demonstrably from a notable locality.
