igneous
Likely basalt (dark volcanic rock)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, with a dull to slightly glassy luster; Mohs hardness about 5–6, no obvious cleavage, and typical specific gravity of 2.8–3.0. The image is blurry, so exact identification is uncertain.
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Physical properties
Fine-grained, dark gray to black, with a dull to slightly glassy luster; Mohs hardness about 5–6, no obvious cleavage, and typical specific gravity of 2.8–3.0. The image is blurry, so exact identification is uncertain.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly at oceanic ridges, hotspots, and continental volcanic fields. It may range from modern to Precambrian in age.
Uses & applications
Used extensively as crushed aggregate, road base, concrete aggregate, building stone, railway ballast, and sometimes decorative stone; ordinary pieces have little jewelry value.
Geological facts
Basalt is the most widespread volcanic rock and forms much of the oceanic crust. Vesicles, if present, may later become filled with zeolites, calcite, or quartz.
Field identification & locations
Look for a uniformly dark, fine-grained texture, substantial weight, and absence of visible large crystals; a streak test is usually weak gray. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic crust.
