mineral

Banded Calcite (Mexican Onyx)

Calcite (Calcium Carbonate, CaCO3)

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

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

Identified May 7, 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 in caves or fissures. This particular banded variety often forms as flowstone or massive deposits over thousands of years.

Uses & applications

Primarily used for ornamental purposes such as carvings, bookends, lamps, and decorative tiles. It is also a popular specimen for crystal healing collectors and as building veneer.

Geological facts

Despite being called 'Onyx' in the trade, it is not true onyx (which is a form of chalcedony/silica). It is much softer than quartz-based onyx and will react (fizz) when exposed to weak acids like vinegar.

Field identification & locations

Look for distinct parallel banding and a soft, waxy to vitreous surface. It can be identified in the field by its characteristic rhombohedral cleavage and its inability to scratch glass.

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