igneous
Polished black stone, likely gabbro or black basalt
Gabbro/basalt; chiefly plagioclase feldspar and pyroxene, possibly minor magnetite
AI-generated identification · may be incorrectDark gray-black, polished, opaque, with faint granular mottling and submetallic reflections; typical hardness about 6–7 Mohs, no visible cleavage, fine- to medium-grained crystalline texture, and specific gravity roughly 2.8–3.1.
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Physical properties
Dark gray-black, polished, opaque, with faint granular mottling and submetallic reflections; typical hardness about 6–7 Mohs, no visible cleavage, fine- to medium-grained crystalline texture, and specific gravity roughly 2.8–3.1.
Formation & geological history
An igneous rock formed when mafic magma cooled slowly underground (gabbro) or rapidly at the surface (basalt), generally from Precambrian to Cenozoic settings. The rounded shape and sheen indicate human tumbling and polishing.
Uses & applications
Used for decorative stone, cabochons, worry stones, aggregates, countertops, and landscaping; ordinary pieces have little gem value.
Geological facts
The specimen may contain magnetite and show weak attraction to a magnet. Its mottled texture distinguishes it from uniformly black glass or dyed agate.
Field identification & locations
Look for tiny interlocking gray crystals, high density, and a non-vitreous granular interior; a streak test is usually gray-black. Common worldwide in oceanic crust, volcanic fields, and mafic intrusions.
