sedimentary

Banded Calcite (Cave Onyx)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

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

Identified May 9, 2026More sedimentary →

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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.