igneous
Likely basalt
Basalt, a fine-grained mafic volcanic rock; exact identification is uncertain from the image alone.
AI-generated identification · may be incorrectDark gray-brown, rough and granular, with no obvious crystals visible. Basalt typically contains plagioclase and pyroxene, sometimes olivine; hardness is about 6 on Mohs, with a generally dull to slightly vitreous luster.
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Physical properties
Dark gray-brown, rough and granular, with no obvious crystals visible. Basalt typically contains plagioclase and pyroxene, sometimes olivine; hardness is about 6 on Mohs, with a generally dull to slightly vitreous luster.
Formation & geological history
Forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface. Basalt occurs from ancient geological periods to recent eruptions.
Uses & applications
Commonly used as crushed aggregate, road stone, and construction material; attractive pieces may be kept as specimens.
Geological facts
Basalt is one of Earth’s most abundant volcanic rocks and forms much of the ocean floor.
Field identification & locations
A dark, dense, fine-grained texture supports basalt identification, but this small, weathered fragment lacks diagnostic features; compare its fresh interior and texture with local rocks.
