igneous
Polished black stone, likely black basalt or gabbro
Basalt/gabbro; primarily plagioclase feldspar and pyroxene, with possible magnetite
AI-generated identification · may be incorrectDark gray to black, fine- to medium-grained, opaque, with a dull to glassy polish and faint pale mineral veins. Hardness about Mohs 6–7; massive, nonfoliated, with no obvious cleavage; specific gravity roughly 2.8–3.1.
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Physical properties
Dark gray to black, fine- to medium-grained, opaque, with a dull to glassy polish and faint pale mineral veins. Hardness about Mohs 6–7; massive, nonfoliated, with no obvious cleavage; specific gravity roughly 2.8–3.1.
Formation & geological history
An igneous rock formed when mafic magma cooled, either rapidly as basalt or slowly underground as gabbro; exact age cannot be determined from the image. The rounded shape and reflective surface indicate water wear and/or human polishing.
Uses & applications
Used for decorative stones, landscaping, countertops, aggregate, monuments, and occasionally cabochons or worry stones.
Geological facts
The pale streaks may be feldspar-rich veins, weathering surfaces, or reflected light rather than a distinct mineral. A magnet test may detect magnetite-bearing basalt.
Field identification & locations
Common in volcanic and oceanic terrains, river gravels, and glacial deposits. Confirm with a fresh broken surface, grain size, streak (typically gray), and acid test; visual identification alone is provisional.
