mineral
Black Onyx
Chalcedony (Silicon Dioxide - SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Deep opaque black; Luster: Vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline quartz); Cleavage: None; Specific Gravity: 2.65-2.66.
- Hardness
- 6
- Color
- Deep opaque black
- Luster
- Vitreous to waxy when polished
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Deep opaque black; Luster: Vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline quartz); Cleavage: None; Specific Gravity: 2.65-2.66.
Formation & geological history
Formed at low temperatures through the deposition of silica-rich fluids in gas cavities (vesicles) within volcanic rocks or sedimentary environments.
Uses & applications
Widely used in lapidary art, jewelry (beads, cabochons, rings), ornamental carvings, and metaphysical collections.
Geological facts
Natural solid black onyx is relatively rare; historically, much commercial black onyx has been created by soaking chalcedony or agate in sugar solutions and then treating with acid to carbonize the sugar into a rich black color.
Field identification & locations
Look for a smooth, opaque black appearance with a waxy to glassy polish and high hardness that resists scratching by steel. Common source regions include Brazil, India, Madagascar, Uruguay, and the United States.
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