sedimentary
Banded Calcite (often sold as 'Mexican Onyx' or 'Calcite Onyx')
Calcite (Calcium Carbonate, CaCO3)
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
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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.
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