mineral
Dark blue-black polished crystal, likely fluorite or slag-like geological material
Tentatively fluorite (CaF₂); identification is uncertain from the image alone
AI-generated identification · may be incorrectOpaque to translucent dark blue-black, vitreous to subvitreous luster, with a faceted or naturally terminated shape and possible surface inclusions. Fluorite has Mohs hardness 4, cubic crystals, perfect octahedral cleavage, and specific gravity about 3.18; color alone is not diagnostic.
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Physical properties
Opaque to translucent dark blue-black, vitreous to subvitreous luster, with a faceted or naturally terminated shape and possible surface inclusions. Fluorite has Mohs hardness 4, cubic crystals, perfect octahedral cleavage, and specific gravity about 3.18; color alone is not diagnostic.
Formation & geological history
If fluorite, it formed in hydrothermal veins and cavities, commonly with quartz, calcite, or sulfides; deposits range from Precambrian to Cenozoic. The visibly shaped surface may indicate cutting or polishing rather than a natural crystal form.
Uses & applications
Fluorite is used industrially as a flux and source of fluorine, and attractive transparent pieces are collected or cut as gemstones. This specimen appears more suitable for casual collecting than jewelry.
Geological facts
Dark fluorite can resemble obsidian, tourmaline, or industrial slag. Fluorite’s cubic cleavage and relatively low hardness are useful distinguishing features.
Field identification & locations
Common sources include China, Mexico, the United States, England, and South Africa. Test cautiously: fluorite scratches with a steel knife but not glass; definitive identification requires cleavage, density, fluorescence, or analytical testing.
