igneous
Likely weathered basalt or iron-rich mafic rock
Basalt; chiefly plagioclase feldspar, pyroxene, and minor olivine/iron oxides
AI-generated identification · may be incorrectDark gray to brown, fine-grained, dull to weakly waxy luster, irregular fracture, and weathered rusty-orange patches from iron oxidation. Typical hardness is about 5–6 Mohs; no obvious cleavage or large crystals are visible.
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Physical properties
Dark gray to brown, fine-grained, dull to weakly waxy luster, irregular fracture, and weathered rusty-orange patches from iron oxidation. Typical hardness is about 5–6 Mohs; no obvious cleavage or large crystals are visible.
Formation & geological history
Likely formed as rapidly cooled volcanic lava, generally in the Cenozoic or older depending on locality, then altered by surface weathering. The image alone cannot establish its exact age or provenance.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and occasionally building stone; this irregular specimen has little commercial or jewelry value.
Geological facts
Its dark color and massive, fine-grained appearance are consistent with basalt, but similar textures occur in other mafic rocks such as diabase or andesite.
Field identification & locations
Look for a dense, fine-grained texture, dark color, and possible tiny feldspar crystals; a streak, magnetism test, acid test, and thin section would improve identification. Common worldwide, especially in volcanic regions.
