gemstone
Black Onyx
Chalcedony (SiO2)
Hardness: 6.5 to 7 on the Mohs scale. Color: Opaque black. Luster: Vitreous to waxy. Crystal structure: Trigonal/Microcrystalline quartz. Cleavage: None. Specific gravity: 2.58 to 2.64.
- Hardness
- 6
- Color
- Opaque black
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5 to 7 on the Mohs scale. Color: Opaque black. Luster: Vitreous to waxy. Crystal structure: Trigonal/Microcrystalline quartz. Cleavage: None. Specific gravity: 2.58 to 2.64.
Formation & geological history
Formed by the deposition of silica in gas cavities of volcanic and sedimentary rocks. Often found in hydrothermal veins and ancient lava flows.
Uses & applications
Widely used in jewelry, carved into cameos and beads, and used for ornamental objects or spiritual purposes.
Geological facts
Onyx has been used since ancient Egyptian times for carving and talismanic jewelry. The name comes from the Greek word 'onux', meaning claw or fingernail.
Field identification & locations
Identified by its uniform jet-black color, conchoidal fracture, and ability to take a high polish. Common sources include Brazil, India, Madagascar, and the USA.
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