sedimentary
Banded Calcite (Mexican Onyx)
Banded Calcite (CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, yellow, honey, brown; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral
- Hardness
- 3 on Mohs scale
- Color
- Cream, yellow, honey, brown
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, yellow, honey, brown; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral
Formation & geological history
Formed by the precipitation of calcium carbonate from cold spring water or groundwater in caves (travertine) or near hot springs. This specimen appears carved into a vessel.
Uses & applications
Used extensively in interior design for sinks, bowls, lamps, and decorative carvings due to its translucency and ease of carving.
Geological facts
Despite being called 'Mexican Onyx' in the trade, it is not true onyx (which is a form of chalcedony/silica). It is a variety of calcite or travertine marble.
Field identification & locations
Identified by its distinctive banding, relative softness (can be scratched by a copper penny), and strong reaction (fizzing) to dilute hydrochloric acid.
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