igneous
Weathered basalt (likely vesicular basalt)
Basalt, a fine-grained mafic volcanic rock; chiefly plagioclase, pyroxene, and iron-magnesium minerals, with possible olivine
AI-generated identification · may be incorrectDark gray-brown, dull to weakly earthy luster, fine-grained and massive, with small weathering pits or vesicles; Mohs hardness about 5–6, no visible cleavage, specific gravity roughly 2.8–3.0
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Physical properties
Dark gray-brown, dull to weakly earthy luster, fine-grained and massive, with small weathering pits or vesicles; Mohs hardness about 5–6, no visible cleavage, specific gravity roughly 2.8–3.0
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; its brown-green surface reflects chemical weathering and oxidation
Uses & applications
Crushed basalt is used for aggregate, road base, railway ballast, and concrete; attractive dense pieces are collected, but this specimen has little commercial value
Geological facts
Basalt is the most common volcanic rock and forms much of oceanic crust; weathered surfaces can develop reddish-brown iron-oxide staining
Field identification & locations
Identify it by its heavy, fine-grained dark interior, lack of visible large crystals, and possible weak magnetism; common in volcanic regions and river gravels worldwide
