igneous
Polished black stone, likely basalt or black jasper
Indeterminate; possible fine-grained basalt (plagioclase–pyroxene) or black jasper/microcrystalline quartz
AI-generated identification · may be incorrectSmooth, rounded and highly polished; opaque black to dark gray with faint brown surface markings and a vitreous-to-waxy luster. Basalt has Mohs hardness ~6, while jasper is ~6.5–7; no crystal faces or cleavage are visible.
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Physical properties
Smooth, rounded and highly polished; opaque black to dark gray with faint brown surface markings and a vitreous-to-waxy luster. Basalt has Mohs hardness ~6, while jasper is ~6.5–7; no crystal faces or cleavage are visible.
Formation & geological history
Could be a naturally waterworn and tumbled volcanic pebble, or a commercially polished stone. Basalt commonly forms from rapidly cooled lava, generally in Cenozoic to older volcanic settings; jasper forms when silica-rich fluids replace or cement sediment.
Uses & applications
Used as a decorative tumbled stone, paperweight, landscaping pebble, or cabochon material. It has little value unless distinctive markings or confirmed gemstone quality are present.
Geological facts
The image cannot reliably distinguish basalt from black jasper, chert, or another dark silicate. A streak, hardness, translucency test, and specific-gravity measurement would help.
Field identification & locations
The reported Arizona location makes basalt, chert/jasper, and volcanic rock plausible. Test whether it scratches glass: basalt usually does weakly or inconsistently; jasper commonly scratches glass. A ceramic streak may be pale gray to white; avoid destructive testing on valuable material.
