igneous
Basalt pebble
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, dull to slightly vitreous luster; hardness about 6 (individual minerals vary), massive texture, and no visible cleavage as a whole rock. The triangular shape appears naturally worn or manually chipped, but the image alone cannot confirm this.
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Physical properties
Fine-grained, dark gray to black, dull to slightly vitreous luster; hardness about 6 (individual minerals vary), massive texture, and no visible cleavage as a whole rock. The triangular shape appears naturally worn or manually chipped, but the image alone cannot confirm this.
Formation & geological history
An extrusive igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly from volcanic eruptions or oceanic crust; ages range from modern to billions of years.
Uses & applications
Widely used as crushed aggregate, road base, railway ballast, riprap, and building stone; attractive polished pieces are used decoratively but have modest jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the oceanic crust. It commonly contains tiny crystals too small to distinguish without magnification.
Field identification & locations
Identify it by its uniform dark color, fine grain, heavy feel, and lack of obvious layering or large crystals; common worldwide in volcanic regions, including Hawaii, Iceland, India, and ocean-floor environments.
