igneous
Tumbled black stone, likely basalt or black jasper
Likely fine-grained basalt (plagioclase–pyroxene); exact identification requires testing
AI-generated identification · may be incorrectOpaque black, smooth polished surface with dull to glassy luster and no visible crystals; typically Mohs 5–6, massive, with poor or indistinct cleavage. The rounded shape indicates human tumbling or water wear.
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Physical properties
Opaque black, smooth polished surface with dull to glassy luster and no visible crystals; typically Mohs 5–6, massive, with poor or indistinct cleavage. The rounded shape indicates human tumbling or water wear.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly during volcanic eruptions from the Cenozoic to Precambrian; if jasper, it is microcrystalline quartz formed by silica-rich groundwater replacement. Commonly sourced from volcanic terrains or gravel deposits.
Uses & applications
Used as a decorative tumbled stone, lapidary material, and occasional jewelry component; basalt is also important for aggregate, roadstone, and construction.
Geological facts
A magnetism test may help: some basalt is weakly magnetic because of magnetite. A streak, hardness, density, and microscopic examination would distinguish basalt from black jasper, obsidian, hematite, or industrial glass.
Field identification & locations
Likely basalt if it feels relatively heavy, has tiny granular texture, and does not scratch glass; likely jasper if it scratches glass and has waxy silica luster. Common sources include India, China, Mexico, and volcanic regions worldwide.
