sedimentary

Banded Calcite (Onyx Marble / Travertine)

Calcite (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness of 3 on the Mohs scale, vitreous to silky or resinous luster, trigonal crystal system, perfect rhombohedral cleavage (often obscured in cryptocrystalline aggregates), distinct swirling parallel bands of pale yellow, cream, and brown, specific gravity around 2.71.

Identified October 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through chemical precipitation from calcium-rich mineral springs or dripping subterranean water in limestone caves (speleothems/travertine). The distinctive banding represents successive deposition layers over time under fluctuating chemical and flow conditions.

Uses & applications

Commonly carved and polished into ornamental and decorative objects such as eggs, bowls, bookends, vases, tiles, and countertops. Popular among crystal healers and lapidary collectors.

Geological facts

Although widely sold commercially under the trade name 'Green Onyx' or 'Mexican Onyx', it is mineralogically calcite or aragonite, not true onyx (which is a banded chalcedony/silica mineral with Mohs hardness 7).

Field identification & locations

Easily identified by its soft nature (readily scratched by a copper coin or steel knife) and vigorous effervescence in dilute hydrochloric acid. Major commercial sources include Pakistan, Mexico, Turkey, and Iran.