sedimentary

Banded Calcite (often sold as 'Mexican Onyx')

Calcite (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

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

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

Identified May 26, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed through the chemical precipitation of calcium carbonate from cold spring water or hydrothermal solutions, often in caves or around hot springs (travertine/tufa).

Uses & applications

Used primarily for decorative objects, spheres, carvings, bookends, and interior design accents like tiles or counters.

Geological facts

Although frequently marketed as 'Onyx', true onyx is a variety of chalcedony (silica). This material is actually a form of banded calcite or travertine which is much softer than real onyx.

Field identification & locations

Identify in the field by its softness (can be scratched by a copper penny) and its strong effervescent reaction to dilute hydrochloric acid. Common in Mexico, Pakistan, and the USA.