sedimentary
Banded Calcite (often sold as Yellow Aragonite or Onyx)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale (soft); Color: Cream, honey yellow, and white bands; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral.
- Hardness
- 3 on Mohs scale (soft)
- Color
- Cream, honey yellow, and white bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale (soft); Color: Cream, honey yellow, and white bands; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral.
Formation & geological history
Formed in caves or hot springs through the precipitation of calcium carbonate from mineral-rich waters. This specific specimen appears to be a water-worn or tumbled river pebble or decorative stone.
Uses & applications
Used primarily for decorative purposes, ornamental carvings, tumbled pocket stones, and in the metaphysical/crystal healing community.
Geological facts
While often commercially mislabeled as 'Onyx' (which is technically a form of chalcedony/silica), 'Mexican Onyx' or 'Cave Onyx' is actually banded calcite. It is much softer than true onyx and can be scratched with a copper penny.
Field identification & locations
Identify in the field by its softness and its reaction to cold dilute hydrochloric acid (it will fizz). Look for rhythmic, parallel color banding. Commonly found in limestone-rich regions and cave systems.
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