mineral

Banded Calcite (often sold as Mexican Onyx)

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale. Color: Creamy white, honey yellow, and brown banding. Luster: Vitreous to pearly. Crystal structure: Trigonal/Hexagonal. Cleavage: Perfect rhombohedral. Specific gravity: 2.71.

Hardness: 3 on Mohs scale
Color: Creamy white, honey yellow, and brown banding
Luster: Vitreous to pearly

Identified June 2, 2026More mineral →

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Physical properties

Formation & geological history

Formation occurs through the precipitation of calcium carbonate from cold spring water or groundwater in caverns. It is often found in sedimentary environments and is relatively young in geological terms compared to igneous rocks.

Uses & applications

Used extensively for decorative carvings, bookends, vases, lampshades, and interior architectural accents like tiles and countertops. It is also a popular collector's specimen.

Geological facts

Despite being commonly called 'Onyx' in the trade, it is actually a form of calcite; true onyx is a variety of chalcedony (quartz). Calcite will react and fizz strongly when exposed to a drop of weak acid such as vinegar.

Field identification & locations

Identified by its distinctive banding, relative softness (can be scratched by a copper coin), and rhombohedral cleavage. Commonly found in Mexico, Pakistan, and the United States (Utah). Collectors look for clarity and high-contrast banding.

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