igneous
Weathered basaltic rock
Fine-grained mafic volcanic rock, likely basalt (composition dominated by plagioclase and pyroxene)
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to weakly vitreous luster, with weathering stains and possible vesicles or fractures. Typical hardness is about 6 on the Mohs scale; cleavage is not visible and specific gravity is commonly 2.8–3.0.
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Physical properties
Dark gray-brown, fine-grained, dull to weakly vitreous luster, with weathering stains and possible vesicles or fractures. Typical hardness is about 6 on the Mohs scale; cleavage is not visible and specific gravity is commonly 2.8–3.0.
Formation & geological history
Likely formed when mafic lava cooled rapidly at or near Earth’s surface; its precise geological age cannot be determined from the image. Brown coloration reflects surface oxidation and weathering.
Uses & applications
Used as crushed aggregate, road base, riprap, railroad ballast, and dimension stone; unexceptional pieces have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms oceanic crust and large lava flows.
Field identification & locations
Identify by its dense, fine texture, dark mafic color, lack of visible large crystals, and relatively high density; common worldwide, especially volcanic regions and oceanic settings.
