mineral

Banded Calcite (often sold as Onyx Marble)

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Cream, tan, brown, and translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal; Gravity: 2.71.

Hardness: 3 on Mohs scale
Color: Cream, tan, brown, and translucent
Luster: Vitreous to waxy

Identified April 4, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: Cream, tan, brown, and translucent; Luster: Vitreous to waxy; Crystal structure: Trigonal; Gravity: 2.71.

Formation & geological history

Formed by the precipitation of calcium carbonate from cold water solutions in caves or hot springs, typically resulting in banded layers of crystals known as flowstone or travertine.

Uses & applications

Used primarily for decorative objects such as spheres, bookends, and figurines; also used in holistic practices and as interior architectural accents.

Geological facts

Despite being called 'Mexican Onyx' or 'Marble Onyx' in the trade, it is actually a form of Calcite; true Onyx is a variety of Chalcedony (silica) and is much harder.

Field identification & locations

Identify by its relative softness (can be scratched by a copper coin) and its reaction to dilute hydrochloric acid (it will fizz). Found globally in limestone karst environments.

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