igneous
Weathered basalt pebble
Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine and iron oxides
AI-generated identification · may be incorrectDark brown to gray, rounded and waterworn, with a dull to slightly waxy luster and no visible crystals; typically hardness 5–6, massive texture, negligible cleavage, and specific gravity about 2.8–3.0.
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Physical properties
Dark brown to gray, rounded and waterworn, with a dull to slightly waxy luster and no visible crystals; typically hardness 5–6, massive texture, negligible cleavage, and specific gravity about 2.8–3.0.
Formation & geological history
Formed when basaltic lava rapidly cooled at or near Earth’s surface, likely millions to billions of years ago, then became rounded by stream, beach, or glacial transport and surface weathering.
Uses & applications
Used as aggregate, roadstone, riprap, and ballast; attractive polished pebbles may be used decoratively, though this specimen has modest gem or collector value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly contains magnetite, making some pieces weakly magnetic.
Field identification & locations
Identify it by its heavy, fine-grained dark body, lack of layering, and possible weak magnetism; common worldwide, especially volcanic regions, river gravels, and beaches. The brown surface likely reflects oxidation and weathering.
