gemstone
Black Onyx
Chalcedony (SiO2)
Hardness: 6.5-7 on the Mohs scale. Color: Solid black. Luster: Vitreous to waxy. Crystal structure: Trigonal/Microcrystalline quartz. Cleavage: None. Specific gravity: 2.60-2.65.
- Hardness
- 6
- Color
- Solid black
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on the Mohs scale. Color: Solid black. Luster: Vitreous to waxy. Crystal structure: Trigonal/Microcrystalline quartz. Cleavage: None. Specific gravity: 2.60-2.65.
Formation & geological history
Formed by the deposition of silica from groundwater in gas cavities of lavas or other rocks. Found worldwide, often in Brazil, India, Madagascar, and the USA.
Uses & applications
Widely used in jewelry such as rings, necklaces, beads, and carved cameos due to its ability to take a high polish and striking contrast when layered.
Geological facts
Black onyx has been used historically for thousands of years in ancient civilizations like Greece and Rome for intaglio and seal rings.
Field identification & locations
Identified by its opaque, deep black color, smooth waxy luster, and conchoidal fracture. Often imitated by treated black chalcedony or glass.
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