igneous
Likely weathered mafic rock (basalt or gabbro)
Basalt–gabbroic rock; chiefly plagioclase feldspar, pyroxene, and possibly olivine
AI-generated identification · may be incorrectDark gray to black, coarse-to-fine crystalline texture, dull to locally vitreous luster, irregular fractures, and apparent vesicles or weathering cavities; hardness about 5–6 and specific gravity roughly 2.8–3.1.
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Physical properties
Dark gray to black, coarse-to-fine crystalline texture, dull to locally vitreous luster, irregular fractures, and apparent vesicles or weathering cavities; hardness about 5–6 and specific gravity roughly 2.8–3.1.
Formation & geological history
Formed from mafic magma cooling at or near Earth’s surface (basalt) or underground (gabbro), generally in volcanic or oceanic-crust settings; the specimen’s exact age and origin cannot be determined from the image.
Uses & applications
Common basalt is used as crushed aggregate, roadstone, riprap, and building stone; attractive polished pieces may be sold as decorative specimens, but this example appears low-grade.
Geological facts
Its dark color reflects iron- and magnesium-rich minerals. Metallic-looking highlights may be fresh pyroxene, mica, or weathered surfaces rather than metal ore.
Field identification & locations
Test for a glassy versus granular texture, check for magnetic response, and use a streak, hardness, and thin-section test for confirmation; common worldwide, especially volcanic regions and oceanic terrains.
