igneous
Dark gray volcanic rock, probably andesite or basalt
Fine-grained mafic–intermediate volcanic rock; likely basalt (plagioclase ± pyroxene), possibly andesite
AI-generated identification · may be incorrectMedium to dark gray, massive and fine-grained with dull to weakly waxy luster; apparent flat fracture surfaces and no visible crystals. Typical hardness is about 5–6 Mohs; specific gravity roughly 2.7–3.0. Identification is tentative because the image does not show diagnostic mineral grains or texture.
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Physical properties
Medium to dark gray, massive and fine-grained with dull to weakly waxy luster; apparent flat fracture surfaces and no visible crystals. Typical hardness is about 5–6 Mohs; specific gravity roughly 2.7–3.0. Identification is tentative because the image does not show diagnostic mineral grains or texture.
Formation & geological history
Formed when lava cooled at or near Earth’s surface, generally during the Cenozoic or older; its exact age cannot be determined visually. The reported northeastern Iran location is geologically plausible for volcanic rocks associated with the Alborz–Azerbaijan region.
Uses & applications
Used as crushed aggregate, roadstone, riprap, and occasionally building or paving stone; attractive dense pieces may be collected, but this specimen has little gem value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust, while andesite is common in volcanic arcs. A streak, acid test, and thin-section examination would help distinguish it from dark metamorphic or sedimentary rocks.
Field identification & locations
Look for a uniformly fine texture, lack of layering, and small feldspar or pyroxene crystals; a magnetic response supports basalt. Common alternatives include dark slate, hornfels, or altered volcanic rock, especially if it splits along planar surfaces.
