igneous
Dark volcanic rock (possibly basalt)
Basalt, a fine-grained mafic volcanic rock; identification is uncertain from the image alone
AI-generated identification · may be incorrectDark brown to black, rough and compact, with no clearly visible crystals. Basalt is typically Mohs 6, mostly plagioclase and pyroxene, and has a fine-grained crystalline texture; hardness and density cannot be confirmed visually.
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Physical properties
Dark brown to black, rough and compact, with no clearly visible crystals. Basalt is typically Mohs 6, mostly plagioclase and pyroxene, and has a fine-grained crystalline texture; hardness and density cannot be confirmed visually.
Formation & geological history
Forms when iron- and magnesium-rich lava cools quickly at or near the surface. Basalt occurs in volcanic settings of many ages, from recent flows to ancient oceanic crust.
Uses & applications
Commonly used as crushed aggregate, road stone, and construction material; attractive pieces may be kept as specimens.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and makes up much of the ocean floor.
Field identification & locations
A basalt identification is supported by the specimen’s dark, dense appearance, but the photo lacks scale and diagnostic detail. Basalt is widespread in volcanic regions and oceanic crust; a fresh surface and hardness test can help distinguish it from other dark rocks.
