sedimentary

Banded Calcite (Onyx Marble)

Calcite (CaCO3) / Travertine

AI-generated identification · may be incorrect

Hardness: 3 on the Mohs scale; Color: Pale yellowish-cream to honey-amber with subtle banding/mottling; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal (microcrystalline/fibrous aggregates); Cleavage: Perfect rhombohedral in coarse crystals, though obscured in compact massive forms;…

Hardness: 3 on the Mohs scale
Luster: Vitreous to waxy when polished

Identified October 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through chemical precipitation of calcium carbonate from mineral-rich spring waters or groundwater in caves (speleothems/travertine) or hydrothermal veins.

Uses & applications

Commonly carved and turned into ornamental objects, eggs, spheres, bookends, tiles, and decorative carvings; frequently traded under the commercial name 'Mexican Onyx' or 'Green/Yellow Onyx'.

Geological facts

Despite being widely marketed as 'onyx', it is composed of calcite or aragonite and is chemically distinct from true silica-based onyx (chalcedony). It reacts briskly with dilute hydrochloric acid.

Field identification & locations

Identifiable by its relatively low hardness (easily scratched by a copper coin or steel blade), smooth translucent waxy appearance, and effervescence with acid. Frequently quarried in Mexico, Pakistan, Turkey, and Italy.