igneous
Likely weathered basalt or iron-rich volcanic rock
Fine-grained mafic igneous rock, possibly basalt; exact identification requires testing
AI-generated identification · may be incorrectDark brown-black, dull to slightly earthy luster, irregular fracture, and apparently fine-grained texture with possible iron-oxide weathering. Typical basalt hardness is about 6 Mohs; no obvious cleavage and specific gravity is commonly 2.8–3.0.
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Physical properties
Dark brown-black, dull to slightly earthy luster, irregular fracture, and apparently fine-grained texture with possible iron-oxide weathering. Typical basalt hardness is about 6 Mohs; no obvious cleavage and specific gravity is commonly 2.8–3.0.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. The brown surface likely reflects oxidation and weathering; its precise age cannot be determined from the image.
Uses & applications
Common basalt is used as crushed aggregate, road base, railway ballast, dimension stone, and occasionally as a decorative specimen. This small, unverified piece has minimal commercial value.
Geological facts
The specimen’s rough, dark appearance is consistent with basalt, but it could also be another iron-rich rock or slag. A magnet test, streak test, fresh-fracture inspection, and hand lens would improve identification.
Field identification & locations
Look for a dense, dark gray-to-black rock with tiny crystals; basalt may show vesicles, while metallic slag can be unusually glassy or bubbly. Common sources include volcanic regions worldwide, especially Hawaii, Iceland, India, and the western United States.
