mineral

Banded calcite (onyx marble)

Calcite, CaCO₃; commonly sold as Mexican or Pakistani onyx marble

AI-generated identification · may be incorrect

Hardness 3 Mohs; cream, honey-brown, gray, and greenish bands; vitreous to pearly luster; translucent in thin layers. It has rhombohedral cleavage and forms dense, layered crystalline masses; visible fibrous or stalactitic banding is common.

Identified September 16, 2026More mineral →

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Physical properties

Formation & geological history

A chemically precipitated carbonate deposit formed when calcium-rich groundwater deposited calcite in caves, springs, or fractures, often over thousands to millions of years. Despite its trade name, onyx marble is not true silicate onyx and is generally not metamorphic marble.

Uses & applications

Used for decorative slabs, carvings, vases, bookends, and polished cabochons; softer than quartz and unsuitable for heavy-wear flooring. Small natural specimens typically have modest collector value.

Geological facts

The strong parallel bands and soft calcite composition distinguish it from agate, which is quartz and much harder. Acid or vinegar can produce effervescence, though testing may damage the specimen.

Field identification & locations

Common sources include Mexico, Pakistan, Turkey, Afghanistan, and Iran. Identify it by banded translucent calcite, rhombohedral cleavage, and hardness low enough to scratch with a steel knife; avoid acid testing on valuable pieces.