sedimentary
Banded Calcite (often sold as 'Mexican Onyx')
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, yellow, brown, and reddish bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal (often massive/fibrous); Cleavage: Perfect rhombohedral (not visible in polished form).
- Hardness
- 3 on Mohs scale
- Color
- Cream, yellow, brown, and reddish bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, yellow, brown, and reddish bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal (often massive/fibrous); Cleavage: Perfect rhombohedral (not visible in polished form).
Formation & geological history
Formed through the chemical precipitation of calcium carbonate from cold water springs or in caves as flowstone/travertine. These specimens are typically from the Holocene or Pleistocene epochs.
Uses & applications
Primarily used for decorative objects like eggs, spheres, bookends, and figurines. Also used in architectural accents and as a 'healing crystal' in metaphysical circles.
Geological facts
Despite the trade name 'Onyx', this is not true onyx (which is a form of chalcedony/quartz). This material is much softer and is chemically related to limestone and marble.
Field identification & locations
Identify in the field by its characteristic parallel banding and its softness; it can be scratched with a copper penny or a knife, and will effervesce (fizz) if a drop of weak acid such as vinegar is applied. Commonly found in Mexico, Turkey, and Pakistan.
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