igneous
Dark mafic igneous rock, likely basalt or gabbro
Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, possibly olivine
AI-generated identification · may be incorrectDark gray to black, fine- to medium-grained, dull to slightly vitreous luster, with interlocking crystalline texture. Estimated Mohs hardness 5–6; cleavage is not apparent in the whole specimen, and density is likely about 2.8–3.1 g/cm³.
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Physical properties
Dark gray to black, fine- to medium-grained, dull to slightly vitreous luster, with interlocking crystalline texture. Estimated Mohs hardness 5–6; cleavage is not apparent in the whole specimen, and density is likely about 2.8–3.1 g/cm³.
Formation & geological history
Formed from iron- and magnesium-rich magma. Basalt crystallizes rapidly at or near the surface, while visually similar gabbro crystallizes slowly underground; age cannot be determined from the photograph.
Uses & applications
Basalt is used as crushed aggregate, paving stone, and occasionally dimension stone; gabbro is used for countertops, tiles, monuments, and aggregate. Small attractive pieces may be collected, but this specimen has little commercial value.
Geological facts
The visible pale specks and dark matrix suggest a mafic rock rather than a single mineral crystal. Exact identification would benefit from a fresh surface, grain-size inspection, streak, magnetism, and density testing.
Field identification & locations
Likely basalt if the grains are microscopic, or gabbro if individual feldspar and pyroxene grains are clearly visible. Common worldwide, especially in volcanic regions, oceanic crust, and mafic intrusions.
