sedimentary

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

Calcite (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

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.

Hardness: 3 on Mohs scale
Color: Pale green, white, cream with brown/orange banding
Luster: Vitreous to waxy

Identified May 17, 2026More sedimentary →

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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.