igneous
Polished dark stone, likely basalt
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, with possible olivine and magnetite
AI-generated identification · may be incorrectDark gray to black, fine-grained, opaque, and commonly weakly magnetic; hardness about 6 Mohs, massive texture, no visible cleavage, and specific gravity roughly 2.8–3.0. The glossy surface appears naturally water-worn or artificially polished.
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Physical properties
Dark gray to black, fine-grained, opaque, and commonly weakly magnetic; hardness about 6 Mohs, massive texture, no visible cleavage, and specific gravity roughly 2.8–3.0. The glossy surface appears naturally water-worn or artificially polished.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic islands, and lava flows. Its exact age cannot be determined from the image; basalt ranges from recent to billions of years old.
Uses & applications
Used extensively as crushed aggregate, road stone, paving, construction blocks, and landscaping material; polished pieces are sold as decorative stones or meditation specimens.
Geological facts
The rounded shape suggests river, beach, or glacial transport, while the reflective black surface may indicate polishing or coating. Small metallic-looking grains could be magnetite.
Field identification & locations
Look for a uniformly fine texture, high density, dark color, and possible attraction to a magnet; a streak test, fresh fracture, and hardness test would help distinguish it from slag or other dark rocks. Common worldwide, especially volcanic regions and oceanic islands.
