igneous
Quartz-bearing dark igneous rock, likely gabbro or basalt
Gabbro/basalt dominated by plagioclase and pyroxene, with minor quartz or calcite
AI-generated identification · may be incorrectDark gray to black, coarse-to-fine crystalline texture, vitreous to dull luster, and irregular fracture; estimated Mohs hardness 5–6. Pale white grains are likely plagioclase, while the translucent honey-colored crystal may be quartz or calcite.
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Physical properties
Dark gray to black, coarse-to-fine crystalline texture, vitreous to dull luster, and irregular fracture; estimated Mohs hardness 5–6. Pale white grains are likely plagioclase, while the translucent honey-colored crystal may be quartz or calcite.
Formation & geological history
Formed from cooling mafic magma, probably in a subsurface intrusion if coarse-grained (gabbro) or as a lava flow if fine-grained (basalt); age cannot be determined from the image. Common in oceanic crust and ancient mafic complexes.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, and dimension stone; attractive specimens are collected but generally have little jewelry value.
Geological facts
Gabbro is the intrusive equivalent of basalt and commonly contains pyroxene, plagioclase, and sometimes olivine or quartz. The specimen may also be a dark metamorphic rock such as amphibolite, which requires thin-section or chemical testing to confirm.
Field identification & locations
Look for visible interlocking crystals, high density, and weak or absent layering; a glassy surface suggests basalt. Common localities include oceanic crust, volcanic regions, and mafic intrusions worldwide.
