igneous
Weathered basalt or volcanic rock
Likely vesicular basalt; composition dominated by plagioclase and pyroxene, with possible iron-oxide alteration
AI-generated identification · may be incorrectDark gray-black, fine-grained, with tan/orange weathering surfaces and glossy black areas; typically Mohs 5–6, dull to slightly vitreous luster, no obvious cleavage, and specific gravity about 2.8–3.1.
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Physical properties
Dark gray-black, fine-grained, with tan/orange weathering surfaces and glossy black areas; typically Mohs 5–6, dull to slightly vitreous luster, no obvious cleavage, and specific gravity about 2.8–3.1.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, likely during the Cenozoic or older volcanic activity; the tan coloration reflects oxidation and surface weathering.
Uses & applications
Common basalt is used as crushed aggregate, road stone, building stone, and occasionally decorative material; this small weathered specimen has mainly educational or modest collecting value.
Geological facts
The black portions may contain pyroxene, magnetite, or glassy volcanic material, while the tan zones may be altered feldspar-rich rock or iron staining.
Field identification & locations
Look for a dense dark fine-grained texture, magnetic response if magnetite-rich, and hardness sufficient to scratch glass weakly; confirm with a fresh surface, streak, and thin-section or chemical testing. Common worldwide in volcanic regions.
