mineral

Tumbled banded calcite (often sold as Mexican onyx or banded onyx)

Calcite, CaCO₃; banded travertine/calcite, not true onyx

AI-generated identification · may be incorrect

Cream to honey-brown with dark bands and a polished, waxy-to-glassy luster; calcite hardness 3 Mohs, trigonal crystal system, and perfect rhombohedral cleavage. The photo does not allow reliable confirmation of the exact material.

Identified October 6, 2026More mineral →

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Physical properties

Formation & geological history

Forms when calcium-carbonate-rich water deposits layers in caves, springs, or other groundwater settings; such deposits can be geologically recent to millions of years old.

Uses & applications

Used for carvings, decorative objects, and inexpensive jewelry; softer than quartz gemstones and scratches readily.

Geological facts

“Onyx” is commonly used commercially for banded calcite, although true onyx is a variety of chalcedony (quartz).

Field identification & locations

Banded colors and relatively low hardness suggest calcite; a drop of dilute acid fizzes on calcite, but avoid testing a finished specimen. Banded calcite is notably quarried in Mexico, Pakistan, and elsewhere.