igneous
Weathered basalt (likely vesicular basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine, with iron-oxide alteration
AI-generated identification · may be incorrectFine-grained, dark gray to black, locally rusty-brown from weathering, with dull to weakly glassy luster and possible small vesicles; hardness about 5–6 Mohs, massive structure, and generally poor or absent cleavage.
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Physical properties
Fine-grained, dark gray to black, locally rusty-brown from weathering, with dull to weakly glassy luster and possible small vesicles; hardness about 5–6 Mohs, massive structure, and generally poor or absent cleavage.
Formation & geological history
An extrusive mafic igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; the exposed surface has undergone oxidation and weathering.
Uses & applications
Used as crushed aggregate, road metal, riprap, railway ballast, building stone, and occasionally as a decorative or lapidary material.
Geological facts
Basalt is the most widespread volcanic rock and forms much of the oceanic crust, including seafloor pillow-lava sequences.
Field identification & locations
Identify it by its dense dark color, fine texture, high specific gravity, and lack of visible large crystals; rusty patches indicate weathering, while vesicles support a volcanic origin. Common around volcanic fields, lava flows, and glacially transported cobbles.
