metamorphic
Onyx (Calcite Onyx / Mexican Onyx)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale. Color: Pale tan, cream, white, yellowish, or beige with fine banding. Luster: Vitreous to resinous or waxy. Crystal structure: Trigonal (microcrystalline calcite/marmor). Cleavage: Perfect rhombohedral in calcite grains, though compact fine-grained mass.
- Hardness
- 3 on Mohs scale
- Luster
- Vitreous to resinous or waxy
Identified More metamorphic →
Explore Onyx (Calcite Onyx / Mexican Onyx) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3 on Mohs scale. Color: Pale tan, cream, white, yellowish, or beige with fine banding. Luster: Vitreous to resinous or waxy. Crystal structure: Trigonal (microcrystalline calcite/marmor). Cleavage: Perfect rhombohedral in calcite grains, though compact fine-grained mass.
Formation & geological history
Formed by precipitation from cold water solutions in caves or hot springs (travertine/calcite onyx) or through low-grade metamorphism of limestone. Commonly found in cave systems and hydrothermal environments.
Uses & applications
Used in ornamental carving, interior decoration, sculptures, countertops, tiles, and as polished collector specimens.
Geological facts
Although true mineralogical onyx is a parallel-banded variety of chalcedony (quartz, Mohs 7), commercial stone trades often label banded calcite or travertine as 'Mexican Onyx' or 'Calcite Onyx'. This soft specimen can be easily scratched with a copper coin or steel nail.
Field identification & locations
Identify in the field by its distinct layered/banded structure, soft hardness (can be scratched by steel), and strong effervescence when exposed to cold dilute hydrochloric acid. Commonly found in Mexico, Pakistan, Italy, and the Southwestern US.
More like this
