igneous
Tumbled dark stone, likely basalt or black jasper
Probable basalt (fine-grained plagioclase–pyroxene rock); exact identification requires testing
AI-generated identification · may be incorrectDark gray-black, rounded and polished, with dull to subvitreous luster and a pale vein or fracture filling. Basalt typically has Mohs hardness 5–6, no visible cleavage, fine interlocking crystals, and specific gravity about 2.8–3.0.
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Physical properties
Dark gray-black, rounded and polished, with dull to subvitreous luster and a pale vein or fracture filling. Basalt typically has Mohs hardness 5–6, no visible cleavage, fine interlocking crystals, and specific gravity about 2.8–3.0.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust; its age may range from modern to billions of years. The pale line may be a calcite, quartz, or weathering vein.
Uses & applications
Common basalt is used as aggregate, road stone, railroad ballast, and building stone; tumbled pieces are sold for decor and metaphysical collections. Typical value is about $2–$15.
Geological facts
The photograph cannot distinguish basalt from black jasper, chert, slag, or another dark stone with certainty. A glassy surface, bubbles, or unusually low density would suggest slag rather than natural basalt.
Field identification & locations
Look for fine grain, occasional tiny pale feldspar crystals, heavy weight, and a streak that is generally gray rather than strongly colored; a steel file can test hardness. Common sources include volcanic regions worldwide, especially Hawaii, Iceland, India, and the Pacific Northwest.
