sedimentary

Banded Calcite (commonly traded as Green Onyx / Travertine Onyx)

Calcite (CaCO3) / Travertine

AI-generated identification · may be incorrect

Hardness 3 on Mohs scale; displays translucent to opaque bands of olive-green, pinkish-brown, cream, and reddish-tan; vitreous to resinous luster when polished; trigonal crystal system; rhombohedral cleavage (though obscured by polishing); specific gravity around 2.71.

Identified October 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via chemical precipitation of calcium carbonate from mineral-rich geothermal springs, groundwater, or limestone caves as travertine or dripstone, often enriched with iron oxide and chlorite/clay impurities that create the multi-colored banding.

Uses & applications

Popular decorative and lapidary stone; extensively carved into polished ornamental eggs, spheres, bookends, vases, bowls, and interior architectural tiles.

Geological facts

Although widely marketed under the commercial name 'Green Onyx' or 'Mexican Onyx', it is mineralogically calcite or aragonite, completely distinct from true silica-based chalcedony onyx. It readily effervesces (fizzes) when exposed to weak acids.

Field identification & locations

Commonly sourced from deposits in Pakistan, Mexico, Turkey, and Iran. Field identification is based on low hardness (easily scratched by a copper coin or steel nail) and strong effervescence in dilute hydrochloric acid or vinegar.