sedimentary

Banded Calcite (Onyx Marble / Travertine)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness 3 on the Mohs scale, vitreous to silky or waxy luster, trigonal crystal system, white to pale green, cream, and reddish-brown coloration from iron oxides; reacts readily with dilute hydrochloric acid.

Identified October 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed chemically by the precipitation of calcium carbonate from mineral-rich spring waters, hot springs, or inside cave systems (speleothems/travertine). Common in geological environments with limestone bedrock.

Uses & applications

Popular lapidary and decorative material carved into ornamental eggs, bowls, bookends, tiles, countertops, and carved animal figurines.

Geological facts

Although commercially marketed as 'Mexican Onyx' or 'Green Onyx', it is mineralogically calcite or aragonite, not true chalcedonic onyx (which is microcrystalline quartz).

Field identification & locations

Can be identified by its softness (easily scratched by a copper coin or steel nail) and strong effervescence with weak acid. Widely sourced from Pakistan, Mexico, Turkey, and Italy.