igneous
Likely basalt or vesicular volcanic rock
Basalt, possibly scoriaceous basalt; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to slightly glassy, with irregular weathered cavities or fractures. Basalt typically has Mohs hardness 5–6, specific gravity about 2.8–3.0, and contains plagioclase, pyroxene, and commonly olivine; it has no prominent cleavage.
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Physical properties
Dark gray to black, fine-grained, dull to slightly glassy, with irregular weathered cavities or fractures. Basalt typically has Mohs hardness 5–6, specific gravity about 2.8–3.0, and contains plagioclase, pyroxene, and commonly olivine; it has no prominent cleavage.
Formation & geological history
Forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows; examples range from ancient Precambrian terrains to modern eruptions. Vesicles form when gas bubbles are trapped during cooling.
Uses & applications
Used extensively as crushed aggregate, roadstone, riprap, railway ballast, and building stone; attractive polished pieces may be collected, though this specimen appears ordinary.
Geological facts
Basalt is the most widespread volcanic rock and makes up much of the oceanic crust. A magnet may show weak attraction if the rock contains abundant magnetite.
Field identification & locations
Identify it by its heavy weight, dark color, fine texture, and lack of visible large crystals; a streak, density, magnetism, and fresh fracture would help distinguish basalt from slag or other dark rocks. Common locations include volcanic regions and oceanic crust exposures.
