sedimentary
Onyx Marble (Banded Calcite)
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale (soft); Color: Cream, tan, and white with translucent banding; Luster: Vitreous to waxy; Structure: Hexagonal/Trigonal; Specific Gravity: 2.71
- Hardness
- 3 on Mohs scale (soft)
- Color
- Cream, tan, and white with translucent banding
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale (soft); Color: Cream, tan, and white with translucent banding; Luster: Vitreous to waxy; Structure: Hexagonal/Trigonal; Specific Gravity: 2.71
Formation & geological history
Formed as a chemical precipitate in cold-water springs or as dripstone in caves (speleothems). Unlike true metamorphic marble, this is a sedimentary deposit of calcium carbonate.
Uses & applications
Used primarily for ornamental carvings, small sculptures, decorative tiles, and vanity tops due to its beauty and ease of carving.
Geological facts
Geologically, 'Mexican Onyx' or 'Onyx Marble' is actually a variety of calcite or aragonite. True onyx is a variety of chalcedony (silica) and is much harder (6.5-7 on Mohs scale).
Field identification & locations
Identify in the field by its softness (can be scratched by a copper penny or steel knife) and its reaction to dilute hydrochloric acid (it will fizz). Commonly found in Mexico, Pakistan, and the American Southwest.
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