igneous
Dark mafic rock, likely basalt
Basalt; chiefly plagioclase feldspar and pyroxene, commonly with olivine and iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, typically dull to mildly vitreous, with hardness about 6 on Mohs scale and no prominent cleavage as a whole. The specimen appears weathered and possibly vesicular, but image resolution prevents confident mineral or texture identification.
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Physical properties
Fine-grained, dark gray to black, typically dull to mildly vitreous, with hardness about 6 on Mohs scale and no prominent cleavage as a whole. The specimen appears weathered and possibly vesicular, but image resolution prevents confident mineral or texture identification.
Formation & geological history
Extrusive igneous rock formed when mafic lava rapidly cooled at or near Earth’s surface; most basalt is Cenozoic or younger, though it occurs throughout geological time. Common in volcanic fields, oceanic crust, lava flows, and glacially transported deposits.
Uses & applications
Widely used as crushed aggregate, road base, riprap, railroad ballast, and building stone; attractive polished varieties are used decoratively, but ordinary pieces have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals and opaque iron oxides.
Field identification & locations
Identify by its black-to-gray color, fine grain, substantial weight, and possible tiny vesicles; a fresh broken surface is more diagnostic than weathered exterior. Common worldwide, especially volcanic regions and areas with glacial drift.
