igneous
Uncertain dark, weathered rock fragment
Possibly basalt or a dark mafic volcanic rock; identification is limited by blur and lighting
AI-generated identification · may be incorrectDark brown-black, dull to slightly earthy luster, irregular granular surface, and no clearly visible crystals or cleavage. Likely hardness about 5–6 Mohs if basalt; specific gravity commonly 2.8–3.1.
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Physical properties
Dark brown-black, dull to slightly earthy luster, irregular granular surface, and no clearly visible crystals or cleavage. Likely hardness about 5–6 Mohs if basalt; specific gravity commonly 2.8–3.1.
Formation & geological history
If basalt, it formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly from volcanic eruptions; its exact age and origin cannot be determined from the image.
Uses & applications
Common basalt is used as aggregate, road stone, paving, riprap, and building material; it has little collector value unless unusually fresh, vesicular, or mineralized.
Geological facts
The specimen appears rounded or weathered, possibly from stream or soil transport. A fresh broken surface, streak test, magnet response, and close-up image would greatly improve identification.
Field identification & locations
Look for fine-grained texture, occasional tiny cavities, weak attraction to a magnet, and a gray-black fresh interior. Common worldwide, especially in volcanic regions.
