sedimentary
Banded Calcite (Onyx Marble)
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, white, and tan bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- Cream, white, and tan bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, white, and tan bands; Luster: Vitreous to waxy; Crystal Structure: Trigonal; Cleavage: Perfect rhombohedral; Specific Gravity: 2.71
Formation & geological history
Formed through the precipitation of calcium carbonate from cold water solutions in caves (as flowstone) or around hot springs (as travertine).
Uses & applications
Commonly used for ornamental carvings, polished points, home decor, and in the metaphysical crystal market.
Geological facts
Though often commercially sold as 'Mexican Onyx' or 'Pakistan Onyx', it is a form of calcite, not true chalcedony onyx. It is soft enough to be carved with simple metal tools.
Field identification & locations
Identify by its distinct parallel banding and relative softness (can be scratched by a copper penny or steel knife). It will react and fizz if exposed to weak acid (diluted HCl).
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