sedimentary

Banded Calcite (often sold as 'Mexican Onyx')

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

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

Identified June 19, 2026More sedimentary →

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Physical properties

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.