sedimentary

Polished banded calcite (often sold as “onyx marble” or Mexican onyx)

Banded calcite; predominantly CaCO₃, usually microcrystalline to fibrous calcite

AI-generated identification · may be incorrect

Hardness 3 on the Mohs scale; translucent cream, orange, red, and greenish bands with vitreous to waxy luster. Rhombohedral calcite cleavage is present, though polishing obscures it; specific gravity is about 2.7.

Identified August 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when mineral-rich groundwater deposits layered calcite in caves, hot springs, or cavities; banding records changing impurities and flow conditions. The polished sphere is a cut human-processed specimen, and its exact geological age cannot be determined visually.

Uses & applications

Used for ornamental objects, spheres, cabochons, decorative stone, and interior facing; it is softer and less durable than quartz-based agate or true onyx. Common commercial material comes from Mexico, Pakistan, Turkey, and South America.

Geological facts

Despite the trade name “onyx,” this material is calcite rather than quartz. Orange-red layers commonly reflect iron-oxide impurities, while green or cream bands may contain clay or other minerals.

Field identification & locations

Identify it by its vivid curved bands, translucency, and softness: a steel knife can scratch calcite, while quartz agate cannot. Typical localities include Mexican cave and spring deposits, especially near Tecali and Puebla.