Orange Calcite (Mexican Onyx)

Physical Properties

Hardness: 3 on Mohs scale; Color: Orange, honey-yellow, or reddish; Luster: Vitreous to waxy; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific gravity: 2.71

Formation & Geological History

Formed in sedimentary environments through chemical precipitation from calcium-rich solutions, often in caves as flowstone or around hot springs (travertine).

Uses & Applications

Commonly used for ornamental carvings (eggs, spheres), architectural accents, and in the metaphysical gemstone market.

Geological Facts

While often called 'Mexican Onyx' in the trade, it is geologically a form of calcite or travertine rather than true onyx (which is chalcedony). It reacts strongly with cold hydrochloric acid.

Field Identification & Locations

Identify by its orange color, waxy luster when polished, and low hardness (can be scratched by a copper coin). Found extensively in Mexico, USA, and Brazil.

Identified on: 5/1/2026

Mode: Standard