mineral
Black Onyx
Chalcedony (SiO2) with parallel banding
Hardness: 6.5-7 (Mohs), Color: Black with white bands, Luster: Vitreous to waxy, Crystal structure: Trigonal/Monoclinic (Cryptocrystalline), Cleavage: None, Specific gravity: 2.65-2.67
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Black with white bands, Luster: Vitreous to waxy, Crystal structure: Trigonal/Monoclinic (Cryptocrystalline), Cleavage: None, Specific gravity: 2.65-2.67
Formation & geological history
Formed by the deposition of silica in gas cavities (vesicles) in volcanic lava flows; the bands result from rhythmic crystallization and varied mineral impurities over time.
Uses & applications
Extensively used in jewelry (rings, beads, pendants), ornamental carvings, and decorative items due to its durability and aesthetic banding.
Geological facts
Unlike agate, which has curved bands, onyx is defined by having parallel bands; it has been used since antiquity for intaglio and cameo engravings.
Field identification & locations
Identified by its distinctive black-and-white parallel stripes and waxy luster when polished. Commonly sourced from Brazil, India, and Madagascar; can be distinguished from obsidian by its higher hardness and internal banding.
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