Onyx (Cave Onyx / Mexican Onyx)
Image: James St. John (CC BY 2.0)
Mineral NameOnyx (Cave Onyx / Mexican Onyx)
Chemical FormulaCaCO3
Mohs Hardness3
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavageperfect rhombohedral
Fractureconchoidal to uneven
Specific Gravity2.71
Colorswhite, cream, tan
Transparencytranslucent to opaque
Type LocalityCrystal Onyx Cave, near Cave City, Kentucky, USA
Mineral GroupCarbonates
Usesdecorative stone, carving, architectural
Associated Mineralsaragonite, calcite
Raritycommon
Description
This image shows a whitish-colored travertine dripstone, commonly known as 'cave onyx' or 'Mexican onyx,' displaying a smooth, banded appearance typical of cave formations.
Geological Context
This material is a form of travertine, composed of calcite, which precipitates from supersaturated groundwater in caves, forming speleothems within limestone and dolostone formations like the Ste. Genevieve Limestone.
