igneous
Dark volcanic rock, likely basalt
Basalt (fine-grained mafic igneous rock; commonly plagioclase, clinopyroxene, and olivine)
AI-generated identification · may be incorrectGray-brown to black, dull to weakly vitreous, irregular angular surface; typically Mohs 6–7, with no visible cleavage and very fine crystalline texture. The image is insufficient to confirm exact mineralogy or density.
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Physical properties
Gray-brown to black, dull to weakly vitreous, irregular angular surface; typically Mohs 6–7, with no visible cleavage and very fine crystalline texture. The image is insufficient to confirm exact mineralogy or density.
Formation & geological history
Forms when low-silica basaltic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Basalt ranges from Precambrian to modern, including active lava flows.
Uses & applications
Used widely as crushed aggregate, road stone, concrete aggregate, and railway ballast; attractive polished pieces may be sold as decorative stone, though this specimen appears ordinary.
Geological facts
Basalt is Earth’s most abundant volcanic rock and commonly forms columnar joints. Vesicles, magnetic response, or small olivine crystals can help distinguish it from similar dark rocks.
Field identification & locations
Common in Hawaii, Iceland, India’s Deccan Traps, oceanic islands, and volcanic regions worldwide. Field tests: usually heavier than similarly sized sedimentary rocks, scratches glass, and may attract a magnet if iron-rich; a fresh broken surface is more diagnostic.
