Banded Calcite (Cave Onyx)

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.

Identified on: 5/9/2026

Mode: Standard