sedimentary
Banded Calcite (Green Onyx)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Green, cream, and tan bands; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Green, cream, and tan bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Green, cream, and tan bands; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Specific gravity: 2.71
Formation & geological history
Formed as a chemical sedimentary rock through the precipitation of calcium carbonate from mineral-rich spring water or groundwater, often in caves or around hot springs (travertine/onyx marble).
Uses & applications
Used primarily for decorative items such as spheres, bookends, and ornaments; also popular in metaphysical collections and as interior design accents like tiles and sink basins.
Geological facts
Despite being commercially marketed as 'Green Onyx,' it is geologically calcite or aragonite, not true onyx (which is a form of chalcedony). It is much softer than quartz-based onyx and will react/fizz if exposed to acid.
Field identification & locations
Identify by its characteristic banding, translucency, and low hardness (can be scratched by a steel blade). Commonly found in Mexico, Pakistan, and Afghanistan. Collectors look for vibrant green banding and lack of fractures.
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