igneous
Dark volcanic rock, likely basalt
Basalt; fine-grained mafic silicate rock dominated by plagioclase and pyroxene, commonly with olivine
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, with a dull to weakly vitreous luster; Mohs hardness about 5–6 and no obvious cleavage. The specimen appears rough and possibly vesicular, but the image is insufficient for a definitive identification.
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Physical properties
Typically dark gray to black, fine-grained, with a dull to weakly vitreous luster; Mohs hardness about 5–6 and no obvious cleavage. The specimen appears rough and possibly vesicular, but the image is insufficient for a definitive identification.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic fields; specimens may range from recent to Precambrian in age.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally dimension stone; common pieces have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. It can resemble dark slag, and a fresh gray streak and lack of metallic appearance help distinguish it.
Field identification & locations
Look for a uniformly fine texture, dark color, and dense weight; small cavities may contain secondary minerals. Common worldwide, especially Hawaii, Iceland, India, and oceanic volcanic regions.
