gemstone
Black Onyx
Chalcedony (SiO2)
Hardness: 6.5-7 on the Mohs scale, Color: Black, Luster: Vitreous to dull, Crystal structure: Trigonal/microcrystalline, Cleavage: None, Specific gravity: 2.60-2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 on the Mohs scale, Color: Black, Luster: Vitreous to dull, Crystal structure: Trigonal/microcrystalline, Cleavage: None, Specific gravity: 2.60-2.65
Formation & geological history
Formed by the deposition of silica in gas cavities of volcanic rocks or groundwaters circulating through sedimentary rock, over millions of years
Uses & applications
Widely used in jewelry, cameos, beads, and ornamental carvings
Geological facts
Black onyx has been used historically since ancient Egyptian and Roman times for seals, signet rings, and protective amulets
Field identification & locations
Identified by its deep opaque black color, waxy-to-vitreous luster when polished, and conchoidal fracture. Common worldwide including Brazil, India, Madagascar, and the USA
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