sedimentary
Banded Calcite (often sold as Mexican Onyx or Aragonite)
Calcite/Aragonite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, tan, brown, and white banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Orthorhombic; Specific Gravity: 2.71.
- Hardness
- 3 on Mohs scale
- Color
- Cream, tan, brown, and white banding
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, tan, brown, and white banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Orthorhombic; Specific Gravity: 2.71.
Formation & geological history
Formed through the chemical precipitation of calcium carbonate from cold or hot spring waters (travertine) or in limestone caves as flowstone. These layers represent different mineral deposition phases over hundreds to thousands of years.
Uses & applications
Primarily used for decorative items like spheres, bookends, and statuettes. In industry, it is used for architectural stone and carvings. It is also a popular specimen for metaphysical collectors.
Geological facts
Despite being called 'Onyx' in the trade, it is not true onyx (which is a form of chalcedony/silica). This material is much softer and is chemically identical to the scales found in kettles or the material of sea shells.
Field identification & locations
Identify in the field by its distinctive parallel banding and extreme softness; it can be scratched by a copper coin or a steel knife. It will also effervesce (fizz) if a drop of weak acid is applied.
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