Banded Calcite (often sold as 'Mexican Onyx' or 'Calcite Onyx')

Physical Properties

Hardness: 3 on Mohs scale; Color: Pale green, white, cream with brown/orange banding; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Specific Gravity: 2.71.

Formation & Geological History

Formed as chemical precipitates in caves (flowstone/dripstone) or near cold/hot springs where calcium-rich waters deposit layers of carbonate over time.

Uses & Applications

Polished for ornamental use, spheres, bookends, statues, and interior decoration such as tabletops or tiles.

Geological Facts

Despite being called 'Onyx' in trade, it is actually a form of calcite; true onyx is a variety of chalcedony (silica) and is much harder.

Field Identification & Locations

Can be identified by its softness (scratched by a copper penny or knife) and its effervescence when exposed to a drop of weak acid. Commonly found in Mexico, Pakistan, and the USA.

Identified on: 5/17/2026

Mode: Standard