mineral

Aragonite (Banded Calcite / 'Mexican Onyx')

Aragonite (Calcium Carbonate - CaCO3)

Hardness: 3.5-4.0 on the Mohs scale; Color: Brown, tan, and cream banding; Luster: Vitreous to waxy; Crystal structure: Orthorhombic; Cleavage: Distinct in one direction; Specific gravity: 2.9–3.0.

Hardness: 3
Color: Brown, tan, and cream banding
Luster: Vitreous to waxy

Identified March 18, 2026More mineral →

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Physical properties

Hardness: 3.5-4.0 on the Mohs scale; Color: Brown, tan, and cream banding; Luster: Vitreous to waxy; Crystal structure: Orthorhombic; Cleavage: Distinct in one direction; Specific gravity: 2.9–3.0.

Formation & geological history

Formed through sedimentary processes in hot springs or caves as stalactitic or stalagmitic deposits. It precipitates from carbonate-rich waters over thousands of years.

Uses & applications

Commonly used for ornamental carvings, bookends, paperweights, and decorative home decor. It is also a popular specimen for crystal healing collectors.

Geological facts

Though often sold as 'Mexican Onyx' or 'Onyx marble,' it is not true onyx (which is a silicate). It is chemically identical to calcite but has a different crystal structure, making it polymorphous.

Field identification & locations

Identify by its characteristic 'bacon-like' parallel banding and softness (can be scratched by a copper penny). Common locations include Mexico, Morocco, and the Southwestern United States (Arizona/Utah).

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