igneous
Rounded basalt pebble
Basalt, a fine-grained mafic volcanic rock; likely plagioclase–pyroxene with possible olivine or iron-oxide alteration
AI-generated identification · may be incorrectDark brown, weathered, and rounded with a dull to weakly glassy luster; fine-grained texture and scattered pale reflective mineral grains. Typical basalt hardness is about Mohs 5–6, with little visible cleavage and specific gravity around 2.8–3.0.
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Physical properties
Dark brown, weathered, and rounded with a dull to weakly glassy luster; fine-grained texture and scattered pale reflective mineral grains. Typical basalt hardness is about Mohs 5–6, with little visible cleavage and specific gravity around 2.8–3.0.
Formation & geological history
Formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; its rounded shape indicates transport by water, waves, or glacial action.
Uses & applications
Common basalt is used as crushed aggregate, roadstone, riprap, and sometimes building stone; this small weathered pebble has minimal commercial or jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the oceanic crust. The brown color likely reflects weathering and oxidation of iron-bearing minerals.
Field identification & locations
Identify it by its heavy feel, fine-grained dark matrix, lack of obvious layering, and magnetic response if magnetite is present; common in volcanic regions, riverbeds, beaches, and glacial deposits.
