sedimentary

Banded Calcite (Green Onyx / Onyx-Marble)

Travertine / Calcite (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on the Mohs scale. Color: Translucent pale green with brown, reddish-brown, and white concentric banding. Luster: Vitreous to waxy/resinous when polished. Crystal Structure: Trigonal (microcrystalline/fibrous). Specific Gravity: ~2.71.

Hardness: 3 on the Mohs scale
Luster: Vitreous to waxy/resinous when polished

Identified October 3, 2026More sedimentary →

Explore Banded Calcite (Green Onyx / Onyx-Marble) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through precipitation of calcium carbonate from mineral-rich spring waters, hot springs, or cave seepages (travertine or flowstone deposits) rich in iron and other trace mineral impurities that cause green and brown banding.

Uses & applications

Commonly used for carved ornamental objects such as eggs, spheres, bowls, figurines, vases, as well as interior architectural decorative tiles and bookends.

Geological facts

Although widely traded under the commercial name 'Green Onyx' or 'Mexican Onyx', it is mineralogically calcite or aragonite, distinct from true geological onyx, which is a cryptocrystalline variety of quartz (chalcedony). It reacts strongly (effervesces) with dilute hydrochloric acid due to its carbonate chemistry.

Field identification & locations

Easily identified by its low hardness (easily scratched by a copper coin or steel nail, unlike true quartz onyx which is hardness 7), banding patterns, and effervescence with acid. Widely sourced from Pakistan, Mexico, Turkey, and Iran.