igneous
Polished orbicular basalt (likely)
Basalt, a fine-grained mafic volcanic rock; dark circular features may be amygdales or orbicules
AI-generated identification · may be incorrectHardness about 6 Mohs; black to dark gray, smooth polished surface, generally dull to submetallic luster, very fine-grained with no visible cleavage. The rounded form appears human-shaped or naturally water-worn.
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Physical properties
Hardness about 6 Mohs; black to dark gray, smooth polished surface, generally dull to submetallic luster, very fine-grained with no visible cleavage. The rounded form appears human-shaped or naturally water-worn.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes. Circular textures may represent gas cavities later filled by minerals or distinctive flow textures.
Uses & applications
Used as a decorative stone, paperweight, cabochon, and lapidary material; basalt is also widely used as aggregate, roadstone, and construction material.
Geological facts
The specimen’s unusually smooth, symmetric shape suggests tumbling or polishing rather than an unmodified field sample. A magnetism test may be positive because basalt commonly contains magnetite.
Field identification & locations
Look for dense dark color, fine grain, high weight, weak magnetism, and resistance to scratching with a steel knife. Common sources include volcanic regions such as India, Mexico, Oregon, and the Mediterranean.
