igneous
Dark mafic igneous rock, likely basalt or gabbro
Basalt–gabbroic rock; chiefly plagioclase feldspar and pyroxene, possibly olivine and iron oxides
AI-generated identification · may be incorrectFine- to medium-grained, dark gray to black, dull to faintly vitreous luster, with interlocking crystals and no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.1.
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Physical properties
Fine- to medium-grained, dark gray to black, dull to faintly vitreous luster, with interlocking crystals and no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.1.
Formation & geological history
Formed from iron- and magnesium-rich magma, probably as a volcanic basalt or slowly cooled intrusive gabbro; likely Phanerozoic, though age cannot be determined from the image.
Uses & applications
Used as aggregate, roadstone, riprap, and building stone; attractive polished pieces may be sold as decorative specimens, usually for modest prices.
Geological facts
The grain size distinguishes varieties: basalt cools rapidly and is fine-grained, whereas gabbro cools underground and is visibly crystalline. The specimen appears weathered and possibly fractured.
Field identification & locations
Common in oceanic crust, volcanic regions, and mafic intrusions worldwide; identify with a hand lens, streak, magnetism, and thin-section or chemical testing. It is not diagnostic enough visually to name precisely.
