igneous
Likely basalt
Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine
AI-generated identification · may be incorrectDark gray to black, dull to faintly glassy, compact and fine-grained; typically Mohs 5–6, with no visible cleavage and irregular fracture. The surface appears weathered, so exact identification from the image is approximate.
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Physical properties
Dark gray to black, dull to faintly glassy, compact and fine-grained; typically Mohs 5–6, with no visible cleavage and irregular fracture. The surface appears weathered, so exact identification from the image is approximate.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic events. It is widespread in oceanic crust, lava flows, and volcanic provinces.
Uses & applications
Used as crushed aggregate, road base, riprap, concrete aggregate, and building stone; attractive polished pieces may be sold as decorative specimens. This small unexceptional piece has minimal commercial value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of Earth’s oceanic crust. Vesicles, tiny crystals, or magnetic response are common diagnostic clues, though none are clearly visible here.
Field identification & locations
Look for a uniformly dark, heavy, fine-grained texture and possible attraction to a strong magnet; a hand lens may reveal tiny pale plagioclase crystals. Common localities include Hawaii, Iceland, India’s Deccan Traps, and ocean-floor volcanic regions.
