Banded Calcite (often sold as Mexican Onyx or Aragonite)

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.

Identified on: 4/29/2026

Mode: Standard