gemstone
Black Onyx
Cryptocrystalline quartz (SiO2)
AI-generated identification · may be incorrectHardness 6.5–7 on the Mohs scale, vitreous to waxy luster, deep opaque black color, trigonal crystal system, and specific gravity of 2.6–2.65.
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Physical properties
Hardness 6.5–7 on the Mohs scale, vitreous to waxy luster, deep opaque black color, trigonal crystal system, and specific gravity of 2.6–2.65.
Formation & geological history
Formed in cavities and gas bubbles of volcanic rocks or sedimentary environments through low-temperature deposition of silica-rich solutions.
Uses & applications
Predominantly fashioned into beads, cabochons, and cameos for jewelry making and ornamental carvings.
Geological facts
Historically prized since antiquity by Romans and Greeks, most commercial black onyx today is produced by dyeing porous chalcedony with carbon solutions.
Field identification & locations
Identified by its high polish, complete opacity, smooth conchoidal fracture, and lack of banding when treated; major sources include Brazil, India, and Madagascar.
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