mineral
Aragonite (Onyx Marble)
Calcium Carbonate (CaCO3), Orthorhombic crystal system
AI-generated identification · may be incorrectHardness: 3.5-4.0 Mohs; Color: Banded honey, cream, and brown; Luster: Vitreous to resinous; Structure: Fibrous or massive; Cleavage: Distinct in one direction.
- Hardness
- 3
- Color
- Banded honey, cream, and brown
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 3.5-4.0 Mohs; Color: Banded honey, cream, and brown; Luster: Vitreous to resinous; Structure: Fibrous or massive; Cleavage: Distinct in one direction.
Formation & geological history
Formed through low-temperature sedimentary processes, typically as precipitates from hot springs (travertine) or in oxidizing zones of ore deposits. Most commercial banded 'onyx' aragonite dates from the Quaternary period.
Uses & applications
Predominantly used for ornamental carvings, figurines, desk accessories, and architectural slabs. It is preferred for decorative art due to its attractive banding and relative softness for carving.
Geological facts
Despite being called 'Mexican Onyx' or 'California Onyx' in the trade, it is chemically a carbonate mineral, not a true silicate onyx (chalcedony). It is a polymorph of calcite, meaning it has the same chemistry but a different crystal structure.
Field identification & locations
Identify in the field by its distinct wavy 'water-like' banding and its reaction (effervescence) to weak hydrochloric acid. Commonly sourced from Mexico, Pakistan, and the Southwestern USA. Collectors look for high translucency and sharp band contrast.
