mineral

Banded Calcite (often commercially called Onyx)

Calcite (Calcium Carbonate, CaCO3)

Hardness: 3 on Mohs scale; Color: Cream, tan, and white banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Cream, tan, and white banding
Luster: Vitreous to waxy

Identified June 20, 2026More mineral →

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Physical properties

Hardness: 3 on Mohs scale; Color: Cream, tan, and white banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Formation & geological history

Formed through the precipitation of calcium carbonate from cold water solutions, often in caves (as flowstone) or around springs. This specimen shows classic sedimentary layering or banding indicative of variable mineral concentration over time.

Uses & applications

Used primarily for decorative objects, carvings, jewelry (pendants/beads), and as architectural accents like tiles and tabletops.

Geological facts

Although sold as 'Onyx' in the stone trade, true Onyx is a variety of Chalcedony (silica). Calcite Onyx is much softer and can be dissolved by weak acids like vinegar.

Field identification & locations

Identify in the field by its distinctive parallel banding and its softness; it can be easily scratched by a copper penny or a steel knife. It will also effervesce (bubble) if a drop of vinegar or diluted HCl is applied.

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