mineral
Onyx (Black Onyx)
Onyx (Silicon Dioxide, SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 (Mohs scale), Color: Black (often dyed), Luster: Vitreous to silky, Crystal Structure: Hexagonal (Trigonal) cryptocrystalline, Cleavage: None, Specific Gravity: 2.65-2.66
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Black (often dyed), Luster: Vitreous to silky, Crystal Structure: Hexagonal (Trigonal) cryptocrystalline, Cleavage: None, Specific Gravity: 2.65-2.66
Formation & geological history
Formed through the deposition of silica in gas cavities (vesicles) in lava. This process occurs in volcanic and sedimentary environments where silica-rich fluids cool over long periods.
Uses & applications
Primary use in jewelry (pendants, rings), decorative carvings, intaglios, and as a gemstone for protective amulets.
Geological facts
Black onyx in jewelry is almost always natural grey chalcedony that has been dyed black to enhance its depth and consistency. It was highly prized in ancient Rome for seals because wax wouldn't stick to it.
Field identification & locations
Identify by its waxy-to-glassy luster, extreme hardness (it will scratch glass), and cooling touch on the skin compared to plastic imitations. Commonly found in Brazil, India, and Madagascar.
