igneous
Dark mafic volcanic rock, likely basalt
Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides
AI-generated identification · may be incorrectHardness about 6 on the Mohs scale; black to dark gray, fine- to medium-grained, generally dull to slightly vitreous, with interlocking crystals and no prominent cleavage. The specimen appears vesicular or strongly weathered, with scattered lighter mineral grains.
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Physical properties
Hardness about 6 on the Mohs scale; black to dark gray, fine- to medium-grained, generally dull to slightly vitreous, with interlocking crystals and no prominent cleavage. The specimen appears vesicular or strongly weathered, with scattered lighter mineral grains.
Formation & geological history
Basalt forms when low-silica, iron- and magnesium-rich lava rapidly cools at or near Earth’s surface; most examples are Cenozoic to Precambrian, depending on locality. Common settings include oceanic crust, volcanic plateaus, lava flows, and rift zones.
Uses & applications
Used as crushed aggregate, road stone, railway ballast, riprap, building stone, and occasionally as polished decorative material; uncommon hand specimens have modest collecting value.
Geological facts
Its dark color reflects abundant ferromagnesian minerals and oxides. Basalt is the most widespread volcanic rock and makes up much of the ocean floor.
Field identification & locations
Identify it by its dense dark color, lack of visible quartz, fine interlocking texture, and heavy feel; a magnet may respond weakly to magnetite. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic islands.
