igneous
Polished black stone, possibly basalt or black jasper
Basalt (fine-grained mafic rock) or microcrystalline quartz if jasper
AI-generated identification · may be incorrectDark gray-black, smoothly polished, opaque, and weakly vitreous to waxy; basalt has Mohs hardness 5–6 and jasper 6.5–7. The rounded triangular shape and uniform color prevent confident identification from the image alone.
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Physical properties
Dark gray-black, smoothly polished, opaque, and weakly vitreous to waxy; basalt has Mohs hardness 5–6 and jasper 6.5–7. The rounded triangular shape and uniform color prevent confident identification from the image alone.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly from Cenozoic to modern volcanic activity; black jasper forms from silica-rich fluids and volcanic sediment, often as nodules. A specimen’s age cannot be determined visually.
Uses & applications
Used as a worry stone, cabochon, decorative object, or inexpensive jewelry material; basalt is also widely used as aggregate and building stone.
Geological facts
The visible pale edge may be a lighter mineral vein or polishing reflection. A streak, hardness, density, and close texture examination would distinguish basalt from jasper, obsidian, or manufactured glass.
Field identification & locations
Common sources include volcanic regions worldwide, while black jasper is especially associated with India, Brazil, Madagascar, and the western United States. Test whether it scratches glass (jasper usually does); avoid destructive testing if valuable.
