sedimentary

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

Calcite (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale (can be scratched by a copper coin); Color: Banded layers of cream, light green, 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 layers of cream, light green, and brown
Luster: Vitreous to waxy

Identified March 25, 2026More sedimentary →

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

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the chemical precipitation of calcium carbonate from cold spring water or groundwater in caves (travertine) and vein deposits. Geological age varies by site but many commercial deposits are from the Cenozoic era.

Uses & applications

Used extensively for decorative carvings, cabochons for jewelry, chess sets, bookends, and interior architectural finishes. Due to its softness, it is mostly used for ornamental objects rather than everyday rings.

Geological facts

Despite being called 'Onyx' in the gemstone trade, it is actually a form of calcite or travertine. True onyx is a variety of chalcedony (silica) with a Mohs hardness of 7. This material is much softer and will react (fizz) if exposed to weak acids like vinegar.

Field identification & locations

Identify in the field by its distinct parallel banding and soft surface that is easily scratched by steel or even a penny. Commonly found in Mexico, Pakistan, and the Southwestern United States. Collectors should look for vibrant green banding and translucency.