Sedimentary
Banded Onyx (Green Onyx)
Banded Calcite or Travertine (CaCO3)
Hardness: 3 on Mohs scale; Color: Light green, cream, white, orange/rust bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Light green, cream, white, orange/rust bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Light green, cream, white, orange/rust bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71
Formation & geological history
Formed as chemical precipitates in hot springs or limestone caves. This 'onyx marble' is composed of concentric layers of calcite or aragonite deposited from cold solution. It is much younger than true metamorphic marble, often Quaternary in age.
Uses & applications
Extensively used for ornamental objects like spheres, bookends, and bowls. It is also used in interior design for back-lit feature walls due to its translucency, and in traditional carvings.
Geological facts
Despite the trade name 'Green Onyx,' it is geologically a form of calcite/travertine and not true onyx (which is a banded cryptocrystalline quartz). It can be easily distinguished by its softness and reaction to dilute acid.
Field identification & locations
Identify in the field by its distinct parallel banding and high level of translucency. It is much softer than quartz (cannot scratch glass) and is commonly found in Pakistan, Mexico, and Iran. Collectors value it for its aesthetic patterns.
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