sedimentary

Banded Calcite (often sold as Mexican Onyx)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Cream, white, and tan with circular/layered banding; Luster: Vitreous to waxy; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral.

Hardness: 3 on Mohs scale
Color: Cream, white, and tan with circular/layered banding
Luster: Vitreous to waxy

Identified May 21, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Cream, white, and tan with circular/layered banding; Luster: Vitreous to waxy; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral.

Formation & geological history

Formed by the precipitation of calcium carbonate from cold water solutions in caves or around warm springs (travertine), often in the Cenozoic era.

Uses & applications

Decorative carvings (eggs, spheres), ornamental architecture, bookends, and holistic gemstone use.

Geological facts

Despite being called 'Onyx' in the trade, it is chemically different from true Onyx, which is a form of chalcedony (silica). Calcite will fizz when in contact with weak acid.

Field identification & locations

Identify in the field by its characteristic banding, softness (can be scratched by a copper penny), and reaction to acid. Often found in Mexico, Pakistan, and the USA.