igneous
Tumbled dark stone, likely basalt
Basalt; fine-grained mafic volcanic rock, commonly composed of plagioclase, pyroxene, and minor olivine
AI-generated identification · may be incorrectAppears smoothly tumbled, dark gray to black, with a dull to slightly vitreous luster and no visible crystals; typical basalt hardness is about 6–6.5 Mohs, with massive texture and no prominent cleavage.
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Physical properties
Appears smoothly tumbled, dark gray to black, with a dull to slightly vitreous luster and no visible crystals; typical basalt hardness is about 6–6.5 Mohs, with massive texture and no prominent cleavage.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes. The image alone cannot establish its exact age or locality.
Uses & applications
Used as aggregate, road stone, building stone, landscaping material, and decorative tumbled rock; common pieces generally have little jewelry value.
Geological facts
Its dark color reflects abundant iron- and magnesium-rich minerals. Similar-looking tumbled material may be gabbro, diabase, slag, or dark jasper, which cannot be distinguished confidently from this photograph.
Field identification & locations
Common worldwide in volcanic regions, including oceanic crust, Hawaii, Iceland, India, and the western United States; a fresh streak is usually gray, and basalt is opaque and lacks the glassy transparency of obsidian.
