igneous
Dark gray rock fragment, likely basalt
Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase and pyroxene, commonly with olivine
AI-generated identification · may be incorrectHardness about 6 on the Mohs scale; dark gray to black, dull to faintly glassy, with a fine-grained interlocking crystal structure. Cleavage is not visible in the rock mass; density is typically 2.8–3.0 g/cm³.
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Physical properties
Hardness about 6 on the Mohs scale; dark gray to black, dull to faintly glassy, with a fine-grained interlocking crystal structure. Cleavage is not visible in the rock mass; density is typically 2.8–3.0 g/cm³.
Formation & geological history
Forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust. Basalt ranges from recent eruptions to rocks billions of years old.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, riprap, and building stone; attractive polished pieces may be used decoratively. This small fragment has negligible commercial value.
Geological facts
The image shows a small angular, dark fragment with a fine texture consistent with basalt, though lighting and resolution prevent definitive identification. Similar-looking alternatives include andesite, dense slag, or dark sedimentary rock.
Field identification & locations
Identify basalt by its uniform fine grain, dark color, hardness, and lack of obvious layers or large crystals; a hand lens and streak/magnet tests can help distinguish it from slag. Common worldwide, especially in volcanic regions and oceanic crust.
