sedimentary

Banded Calcite (often sold as 'Onyx Marble' or 'Mexican Onyx')

Calcite (CaCO3) / Travertine

AI-generated identification · may be incorrect

Hardness: 3 on the Mohs scale; Color: Cream, tan, brown, and reddish-brown concentric bands; Luster: Vitreous to resinous (high polish); Cleavage: Perfect rhombohedral in raw crystal form; Specific Gravity: ~2.71

Hardness: 3 on the Mohs scale
Color: Cream, tan, brown, and reddish-brown concentric bands
Luster: Vitreous to resinous (high polish)

Identified October 3, 2026More sedimentary →

Explore Banded Calcite (often sold as 'Onyx Marble' or 'Mexican Onyx') in the encyclopedia →

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Physical properties

Formation & geological history

Formed chemically by the precipitation of calcium carbonate from hot springs, geothermal waters, or cave environments (flowstone/travertine), resulting in distinct rhythmic banding layers over time.

Uses & applications

Commonly carved and polished into ornamental decorative objects such as eggs, spheres, bowls, vases, and tiles. Due to low hardness, it is not suitable for faceted jewelry rings.

Geological facts

Although trade names often refer to this material as 'onyx' or 'green/red onyx,' true onyx is a cryptocrystalline variety of quartz (silicon dioxide, Mohs 7). Banded calcite is much softer (Mohs 3) and will effervesce (fizz) vigorously in dilute hydrochloric or warm vinegar.

Field identification & locations

Easily identified by its distinct banded layers, relatively soft surface (scratches easily with a copper penny or steel blade), and reaction to weak acid. Highly common in Mexico, Pakistan, Turkey, and Italy.