mineral

Banded Calcite (Mexican Onyx)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Cream, tan, and brown banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral.

Hardness: 3 on Mohs scale
Color: Cream, tan, and brown banding
Luster: Vitreous to waxy

Identified May 3, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: Cream, tan, and brown 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 (as flowstone) or around hot springs (travertine). Often found in hydrothermal veins.

Uses & applications

Used extensively for decorative carvings, spheres, bookends, and interior tiling. Also popular in metaphysical circles and as accessible collector specimens.

Geological facts

Despite being commonly called 'Mexican Onyx' or 'Onyx Marble,' it is a calcite mineral and not a true silicate onyx. It is much softer and more reactive than real onyx.

Field identification & locations

Identify by its characteristic parallel banding and its softness; it can be scratched by a copper penny or steel knife. It will also effervesce (fizz) when in contact with dilute hydrochloric acid.