igneous
Dark volcanic rock, likely basalt
Basalt (fine-grained mafic rock; chiefly plagioclase feldspar and clinopyroxene, commonly with olivine and iron-titanium oxides)
AI-generated identification · may be incorrectTypically black to dark gray, fine-grained, dull to weakly glassy, with hardness about 6–7 and no obvious cleavage; commonly dense, though the specimen appears somewhat vesicular or weathered.
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Physical properties
Typically black to dark gray, fine-grained, dull to weakly glassy, with hardness about 6–7 and no obvious cleavage; commonly dense, though the specimen appears somewhat vesicular or weathered.
Formation & geological history
Forms when low-silica basaltic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust. It may range from recent eruptions to Precambrian age, depending on location.
Uses & applications
Used extensively as crushed aggregate, road base, railway ballast, riprap, and construction stone; attractive polished basalt is used decoratively. Ordinary hand specimens generally have minimal market value.
Geological facts
The image is consistent with basalt but cannot establish a precise identification from appearance alone; scoria or another dark volcanic rock is also possible.
Field identification & locations
Look for a uniformly fine texture, high density, dark color, and possible tiny gas cavities; a streak test, magnet response, and fresh broken surface help distinguish it from slag. Common worldwide, especially volcanic regions and oceanic settings.
