mineral
Banded Calcite (Mexican Onyx)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, white, and tan bands; Luster: Vitreous to pearly; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral; Sg: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Cream, white, and tan bands
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, white, and tan bands; Luster: Vitreous to pearly; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral; Sg: 2.71
Formation & geological history
Formed through the precipitation of calcium carbonate from cold spring water or groundwater in caves and limestone crevices. This process creates distinct layers or 'bands' over time.
Uses & applications
Used extensively in decorative carvings, chess sets, bookends, jewelry (though soft), and architectural accents.
Geological facts
Despite being nicknamed 'Mexican Onyx,' it is geologically a type of calcite or aragonite, not true chalcedony onyx. It is soft enough to be carved with simple metal tools.
Field identification & locations
Identified by its parallel banding and extreme softness; it can be scratched by a copper penny or a knife. It will effervesce (fizz) if a drop of weak acid is applied.
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