igneous
Dark weathered stone, possibly basalt
Fine-grained mafic rock, tentatively basalt (plagioclase–pyroxene ± olivine)
AI-generated identification · may be incorrectAppears dark brown-gray, opaque, dull to slightly earthy, and fine-grained; hardness likely about 6 on the Mohs scale, with no visible cleavage or crystals. Surface weathering and the blurred image prevent reliable confirmation.
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Physical properties
Appears dark brown-gray, opaque, dull to slightly earthy, and fine-grained; hardness likely about 6 on the Mohs scale, with no visible cleavage or crystals. Surface weathering and the blurred image prevent reliable confirmation.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields and oceanic crust; its age cannot be determined from the photograph.
Uses & applications
Unusual hand specimens are mainly collectible; larger basalt is widely used as crushed aggregate, road metal, riprap, and occasionally building stone.
Geological facts
Basalt is the most common volcanic rock and commonly contains microscopic plagioclase and pyroxene crystals. Brown coloration may result from iron-oxide weathering.
Field identification & locations
Look for a uniformly fine texture, high density, dark gray-black fresh surfaces, and possible tiny vesicles; a streak, magnet test, fresh break, and magnification would help distinguish basalt from weathered chert, ironstone, or slag. Common worldwide, especially volcanic regions.
