Onyx (Calcite variety)
Image: James St. John (CC BY 2.0)
Mineral NameOnyx (Calcite variety)
Chemical FormulaCaCO3
Mohs Hardness3
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavageperfect rhombohedral
Fractureconchoidal to uneven
Specific Gravity2.71
Colorswhite, cream, brown, green, pink
Transparencytranslucent
Type LocalityCrystal Onyx Cave, near Cave City, Kentucky, USA
Mineral Groupcarbonates
Usesdecorative stone, carvings, countertops, architectural material
Associated Mineralslimestone, dolostone
Raritycommon
Description
A large, whitish, banded dripstone formation, characteristic of travertine, exhibiting translucent layers and a smooth, polished appearance.
Geological Context
This onyx, a form of travertine composed of calcite, forms in caves through the precipitation of calcium carbonate from mineral-rich water. It is found in a Tertiary-Quaternary cave environment, specifically in Crystal Onyx Cave, Kentucky, where the cave walls are limestone and dolostone.
