mineral

Banded Calcite (often commercially called 'Mexican Onyx')

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale (can be scratched by a copper coin); Color: Banded white, tan, and brown; Luster: Vitreous to waxy; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Hardness: 3 on Mohs scale (can be scratched by a copper coin)
Color: Banded white, tan, and brown
Luster: Vitreous to waxy

Identified March 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the precipitation of calcium carbonate from cold spring water or hydrothermal solutions, often in caves or around hot springs (travertine). Geological age varies by deposit, typically ranging from thousands to millions of years old.

Uses & applications

Commonly used for decorative carvings, cabochons, interior architecture (tiles and countertops), and as a popular 'healing' crystal or beginner's geological specimen.

Geological facts

Despite being called 'Onyx' in the trade, true onyx is a variety of chalcedony (silica), whereas this specimen is calcite. It is much softer than real onyx and will react (fizz) if a drop of weak acid such as vinegar is applied to an unpolished surface.

Field identification & locations

Identify in the field by its softness (can be scratched with a steel knife or copper penny) and its banding. Common locations include Mexico, Pakistan, and various limestone-rich mountain ranges globally. Collectors should look for translucent edges and distinct color layers.

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