sedimentary
Banded Calcite (often sold as 'Mexican Onyx' or 'Green Onyx')
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale. Color: Banded patterns of green, white, brown, and cream. Luster: Vitreous to silky. Crystal structure: Trigonal (often microcrystalline in this form). Cleavage: Perfect rhombohedral. Specific gravity: 2.71.
- Hardness
- 3 on Mohs scale
- Color
- Banded patterns of green, white, brown, and cream
- Luster
- Vitreous to silky
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Physical properties
Hardness: 3 on Mohs scale. Color: Banded patterns of green, white, brown, and cream. Luster: Vitreous to silky. Crystal structure: Trigonal (often microcrystalline in this form). Cleavage: Perfect rhombohedral. Specific gravity: 2.71.
Formation & geological history
Formed as a chemical sedimentary precipitate from cold-water springs or in caves as dripstone (travertine). Layers are deposited over time, often containing impurities like iron or copper that create the distinct color bands.
Uses & applications
Used primarily for ornamental purposes including sculptures, spheres, bookends, vases, and interior design accents like tiles or sink basins.
Geological facts
Despite being called 'Onyx' in the trade, it is not true Onyx (which is a form of chalcedony/quartz). This material 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 distinct parallel banding. It is commonly found in Mexico, Pakistan, and Turkey.
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