igneous
Black volcanic rock, likely basalt
Basalt; primarily plagioclase feldspar and pyroxene, commonly with minor olivine or magnetite
AI-generated identification · may be incorrectTypically fine-grained, dark gray to black, with a dull to weakly vitreous luster; Mohs hardness about 6, massive texture, and no prominent cleavage. The specimen appears dense and angular, though the image cannot confirm its exact mineralogy.
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Physical properties
Typically fine-grained, dark gray to black, with a dull to weakly vitreous luster; Mohs hardness about 6, massive texture, and no prominent cleavage. The specimen appears dense and angular, though the image cannot confirm its exact mineralogy.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hot-spot environments. It may range from ancient Precambrian lava to recent eruptions.
Uses & applications
Used extensively as crushed aggregate, roadstone, railway ballast, building stone, and sometimes basalt fiber; attractive polished pieces are used decoratively. Common hand specimens generally have little monetary value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Vesicles, if present, indicate gas bubbles in the lava; magnetic attraction may result from magnetite.
Field identification & locations
Identify it by its black, fine-grained, heavy appearance and lack of visible large crystals; a glassy surface could instead indicate obsidian, while strong layering may suggest another rock. Common worldwide, especially in volcanic regions and oceanic crust.
