mineral

Banded Calcite (Mexican Onyx)

Calcite (CaCO3)

Hardness: 3 on Mohs scale; Color: Yellow, orange, white, and brown banding; Luster: Vitreous to waxy; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Hardness: 3 on Mohs scale
Color: Yellow, orange, white, and brown banding
Luster: Vitreous to waxy

Identified April 19, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: Yellow, orange, white, and brown banding; Luster: Vitreous to waxy; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Formation & geological history

Formed through the precipitation of calcium carbonate from cold spring water or groundwater in caves and crevices. This specimen shows classic sedimentary deposition layers over time.

Uses & applications

Used primarily for decorative carvings, ornamental stones, bookends, jewelry (beads/cabochons), and as architectural accents like tiles or sink basins.

Geological facts

While often called 'Onyx' in the trade, it is actually a form of calcite or aragonite; true onyx is a variety of chalcedony (silica) and is much harder than this material.

Field identification & locations

Identify in the field by its softness (can be scratched with a copper penny or steel knife) and its reaction to dilute hydrochloric acid (it will fizz/effervesce). Found extensively in Mexico, Pakistan, and the Southwestern US.