sedimentary

Banded Calcite (often commercially sold as Mexican Onyx or Green Onyx)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Pale green with cream, white, and rusty brown banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Rhombohedral; Specific Gravity: 2.71.

Hardness: 3 on Mohs scale
Color: Pale green with cream, white, and rusty brown banding
Luster: Vitreous to waxy

Identified March 18, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Pale green with cream, white, and rusty brown banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Rhombohedral; Specific Gravity: 2.71.

Formation & geological history

Formed in caves (as travertine) or by cold spring water precipitation where mineral-rich water deposits layers of calcite over time. These deposits are typically from the Cenozoic era, though age varies by specific deposit site.

Uses & applications

Primarily used for decorative ornaments, carvings, chalices, chess sets, and architectural accents like lamps or tiles. It is too soft for heavy jewelry use but popular in decorative home goods.

Geological facts

Despite being called 'Onyx' in the trade, it is not true onyx (which is a variety of chalcedony/silica). It is a variety of travertine calcite. One famous historical use includes the carving of small vessels in ancient Egypt and Mesopotamia.

Field identification & locations

Identify by its relative softness (can be scratched by a copper penny or steel knife) and its reaction to dilute hydrochloric acid (it will fizz). Commonly found in Mexico, Pakistan, and Turkey. For collectors, look for translucency and distinct, high-contrast banding.