sedimentary

Banded Calcite Onyx (Cave Onyx / Mexican Onyx)

Calcite (CaCO3) / Travertine

AI-generated identification · may be incorrect

Hardness of 3 on Mohs scale, effervesces in acid, displays distinct colored bands (often green, brown, white, and reddish due to impurities like iron and copper), vitreous to dull luster, rhombohedral cleavage (though massive in this form).

Identified September 15, 2026More sedimentary →

Explore Banded Calcite Onyx (Cave Onyx / Mexican Onyx) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through chemical precipitation from cold or hot spring waters, or in limestone caves as stalactites, stalagmites, and flowstone. As water evaporates or loses carbon dioxide, calcium carbonate precipitates out, creating bands over time.

Uses & applications

Commonly carved into decorative items such as vases, bowls, chess sets, and small sculptures. Also used for ornamental stonework and sometimes in jewelry.

Geological facts

Often mislabeled commercially as 'Onyx', which is geologically a banded variety of chalcedony (quartz). True onyx has a hardness of 7, whereas this material is much softer (hardness 3).

Field identification & locations

Can be identified by its softness (can be scratched by a copper coin or knife) and its reaction to weak acid. Mostly found in locations with extensive limestone cave systems or hot springs, such as Mexico and Pakistan.