Onyx
Image: James St. John (CC BY 2.0)
Mineral NameOnyx
Chemical FormulaCaCO3
Mohs Hardness3
Crystal Systemcubic
Lustervitreous
Streak ColorWhite
CleavagePerfect rhombohedral on {1011}
FractureConchoidal to uneven
Specific Gravity2.71
Colorswhite, cream, brown, yellow, green, pink
TransparencyTranslucent to opaque
Type LocalityCrystal Onyx Cave, near Cave City, Kentucky, USA
Mineral GroupCarbonates
Usesdecorative stone, carvings, jewelry, architectural material
Raritycommon
Description
The image displays whitish, banded stalactites, which are cave formations composed of travertine, a form of calcite commonly known as onyx marble or Mexican onyx.
Geological Context
These formations occur in a Tertiary-Quaternary cave within limestones and dolostones of the Ste. Genevieve Limestone in Kentucky, USA. They are formed by the slow deposition of calcite from supersaturated mineral-rich water.
