igneous
Gabbroic or basaltic rock with weathered veins
Likely mafic igneous rock, possibly olivine gabbro or porphyritic basalt; exact identification requires testing
AI-generated identification · may be incorrectDark gray-black, fine- to medium-grained, with abundant tan-brown weathering products and possible feldspar/olivine crystals; typically vitreous to dull, Mohs hardness about 5–7, massive texture, and no obvious cleavage. Brown areas may be iron-oxide alteration or a mineral vein.
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Physical properties
Dark gray-black, fine- to medium-grained, with abundant tan-brown weathering products and possible feldspar/olivine crystals; typically vitreous to dull, Mohs hardness about 5–7, massive texture, and no obvious cleavage. Brown areas may be iron-oxide alteration or a mineral vein.
Formation & geological history
Formed from cooling iron- and magnesium-rich magma, either underground as gabbro or at the surface as basalt; alteration and weathering likely occurred later. Precise geological age and setting cannot be determined from the photograph.
Uses & applications
Common equivalents are used as crushed aggregate, road stone, riprap, and occasionally dimension stone; attractive polished pieces may be collected but are generally not gemstone material.
Geological facts
The dark color reflects abundant mafic minerals such as pyroxene, amphibole, or olivine. A streak, magnetism, hardness, and fresh-break examination would help distinguish basalt, gabbro, and altered ultramafic rock.
Field identification & locations
Common in oceanic crust, volcanic regions, and exposed mafic intrusions worldwide; look for interlocking crystals, weak magnetism, and a pale gray streak. The specimen appears tumbled or naturally rounded, obscuring its original texture.
