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 greens, creams, and rust-browns; 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 greens, creams, and rust-browns
Luster: Vitreous to waxy

Identified March 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a chemical sedimentary rock through the precipitation of calcium carbonate from cold spring water or groundwater in caverns (travertine/stalagmitic formation). This material is often relatively young in geological terms, dating from the Quaternary period.

Uses & applications

Primarily used for decorative carvings, ornaments, chess sets, small sculptures, and household items like the chalice pictured. Also used in interior design for tiles and countertops.

Geological facts

Despite being called 'Onyx' in the trade, it is not true onyx (which is a form of chalcedony/silica). Because it is made of calcite, it will react and fizz if it comes into contact with even weak acids like vinegar or lemon juice.

Field identification & locations

Identify in the field by its distinct colorful banding and softness compared to quartz. It is commonly found in Mexico, Pakistan, and Turkey. For collectors, look for translucency and the absence of deep scratches, which are common due to the material's softness.