sedimentary

Banded Calcite (often sold as 'Mexican Onyx')

Calcite (Calcium Carbonate - CaCO3)

Hardness: 3 on Mohs scale. Color: Naturally white, cream, or brown, but this specimen is artificially dyed green, yellow, and red. Luster: Vitreous to pearly. Structure: Hexagonal/Trigonal. Cleavage: Perfect rhombohedral. Specific Gravity: 2.71.

Hardness: 3 on Mohs scale
Luster: Vitreous to pearly

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of calcium carbonate from cold water solutions, often in caves or around hot springs (travertine). Usually Holocene to Pleistocene in geological age.

Uses & applications

Primarily used for decorative carvings, ornaments, chess sets, and as minor architectural stone. Not suitable for jewelry rings due to low hardness.

Geological facts

Despite being called 'Onyx' in the trade, it is not true onyx (which is a form of cryptocrystalline quartz). This material is much softer and will react (fizz) when in contact with dilute hydrochloric acid.

Field identification & locations

Identify by its parallel banding patterns, soft waxy feel, and susceptibility to scratches with a copper penny or steel knife. Commonly found in Mexico, Pakistan, and Turkey. Collectors should look for evenness in the banding.

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