sedimentary

Banded Calcite (Onyx Marble / Green Onyx)

Travertine / Banded Calcite (CaCO3)

AI-generated identification · may be incorrect

Mohs hardness 3; vitreous to resinous luster; translucent to opaque; concentric to parallel banding of green, cream, brownish-red, and yellow; trigonal crystal system (microcrystalline/fibrous); specific gravity ~2.71.

Identified October 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a chemical sedimentary deposit around mineral springs, hot springs, or cave interiors through rapid calcium carbonate precipitation from saturated bicarbonate solutions.

Uses & applications

Commonly carved and polished into ornamental decorative objects such as eggs, spheres, bookends, vases, tiles, and countertops.

Geological facts

Often commercially marketed as 'Onyx' or 'Green Onyx', it is actually a variety of calcite or travertine (calcium carbonate) rather than true silica-based onyx (chalcedony).

Field identification & locations

Can be distinguished from true agate/onyx by its low hardness (easily scratched by a steel blade) and effervescence with dilute hydrochloric acid. Frequently sourced from Pakistan, Mexico, Iran, and Turkey.