igneous
Dark igneous rock, likely basalt
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, with a dull to slightly vitreous luster; Mohs hardness about 5–6, poor cleavage as a rock, and specific gravity roughly 2.8–3.0. The blurred image may also show a vesicular or weathered surface.
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Physical properties
Typically dark gray to black, fine-grained, with a dull to slightly vitreous luster; Mohs hardness about 5–6, poor cleavage as a rock, and specific gravity roughly 2.8–3.0. The blurred image may also show a vesicular or weathered surface.
Formation & geological history
Basalt forms when low-silica magma cools rapidly at or near Earth’s surface, commonly in lava flows, oceanic crust, and volcanic islands. It ranges from very recent eruptions to rocks billions of years old.
Uses & applications
Widely used as crushed aggregate, road base, riprap, railway ballast, building stone, and occasionally polished architectural material; generally has little gem value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals and iron oxides.
Field identification & locations
Identify it by its black-to-dark-gray color, dense fine grain, heavy feel, and absence of visible large crystals; a magnet may respond weakly. Common worldwide, especially in volcanic regions and oceanic terrains.
