sedimentary
Banded Calcite (Cave Onyx)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Tan, brown, white, and golden bands; Luster: Vitreous to pearly; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral.
- Hardness
- 3 on Mohs scale
- Color
- Tan, brown, white, and golden bands
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 3 on Mohs scale; Color: Tan, brown, white, and golden bands; Luster: Vitreous to pearly; Crystal structure: Trigonal; Cleavage: Perfect rhombohedral.
Formation & geological history
Formed through the precipitation of calcium carbonate from dripping water in caves or hot springs, often creating stalactites, stalagmites, or flowstone layers over thousands of years.
Uses & applications
Used primarily for ornamental objects, carvings, jewelry, interior decoration involving tiles or slabs, and as a popular specimen for rock collectors.
Geological facts
Although often called 'Onyx' in the trade, it is actually a form of calcite; true onyx is a variety of chalcedony (silica). This material is much softer and can be dissolved by acids.
Field identification & locations
Identifiable by its distinct layered banding and its softness (can be scratched by a copper penny). It will effervesce (fizz) when in contact with weak hydrochloric acid.
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