sedimentary
Banded Calcite (often sold as 'Onyx')
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, white, and honey-yellow bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Cream, white, and honey-yellow bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, white, and honey-yellow bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71
Formation & geological history
Formed through the precipitation of calcium carbonate from cold water solutions in caves (as flowstone) or around hot springs (as travertine). The distinct banding represents different stages of mineral deposition and impurity variations.
Uses & applications
Used primarily for decorative objects such as spheres, bookends, and lamp bases. It is also common in jewelry and as an ornamental building stone for interiors.
Geological facts
While commonly sold as 'Onyx' in the decorative trade, true onyx is a variety of chalcedony (silica). Calcite 'onyx' is much softer and will react (fizz) with weak acids like vinegar.
Field identification & locations
Identify by its relative softness (can be scratched by a copper penny or steel knife) and its characteristic translucency and parallel banding. Commonly found in Mexico, Pakistan, and Turkey.
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