igneous
Black basalt (likely vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine, with minor iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, generally dull to weakly vitreous; Mohs hardness about 6, no cleavage as a rock, and typically dense (specific gravity roughly 2.8–3.0). The visible small cavities suggest vesicles, though the surface may also be fractured or weathered.
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Physical properties
Fine-grained, dark gray to black, generally dull to weakly vitreous; Mohs hardness about 6, no cleavage as a rock, and typically dense (specific gravity roughly 2.8–3.0). The visible small cavities suggest vesicles, though the surface may also be fractured or weathered.
Formation & geological history
An extrusive igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during volcanic eruptions. Basalt ranges from recent lava flows to rocks billions of years old.
Uses & applications
Widely used as crushed aggregate, road base, railroad ballast, dimension stone, and building material; attractive polished pieces are used decoratively. Ordinary hand specimens generally have little commercial value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the oceanic crust, including mid-ocean ridges and many large lava plateaus.
Field identification & locations
Identify it by its uniformly dark, fine-grained appearance, high density, and occasional vesicles; a streak test is usually gray to black. Common localities include Hawaii, Iceland, India’s Deccan Traps, oceanic islands, and volcanic regions worldwide.
