sedimentary
Banded Calcite Spheres (Honey Onyx)
Calcite (CaCO3)
Hardness: 3 (Mohs scale). Color: Honey yellow, amber, white, cream. Luster: Vitreous to waxy when polished. Crystal structure: Trigonal/Hexagonal. Cleavage: Perfect rhombohedral.
- Hardness
- 3 (Mohs scale)
- Color
- Honey yellow, amber, white, cream
- Luster
- Vitreous to waxy when polished
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Physical properties
Hardness: 3 (Mohs scale). Color: Honey yellow, amber, white, cream. Luster: Vitreous to waxy when polished. Crystal structure: Trigonal/Hexagonal. Cleavage: Perfect rhombohedral.
Formation & geological history
Formed in caves or thermal springs as travertine/onyx, where calcium carbonate precipitates from groundwater over long periods, creating characteristic bands.
Uses & applications
Used primarily for decorative objects like spheres, eggs, and bookends. In larger forms, it is used for floor tiles and architectural accents.
Geological facts
Despite being called 'Onyx' in the trade, it is actually a form of banded calcite. Real onyx is a variety of chalcedony (silica) and is much harder (7 vs 3).
Field identification & locations
Identify by its relative softness (can be scratched by a copper penny or steel) and its reaction (effervescence) to weak acids like vinegar. Common in Mexico and Pakistan.
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