Travertine rimstone in a Tertiary-Quaternary cave in Kentucky, USA.
Crystal Onyx Cave is a relatively small, speleothem-rich cave on the eastern flank of Prewitts Knob, southwest of the town of Cave City, Kentucky, USA. The walls of the cave are limestones and dolostones of the Ste. Genevieve Limestone (upper Middle Mississippian).
Crystal Onyx Cave was discovered in 1960 as a sinkhole. The name of the cave refers to the whitish-colored travertine (composed of calcite). Fifty-three Indian bones dating to about 680 B.C. were found wrapped up at the bottom of the main shaft of this cave.
The structures shown above are examples of "speleothem", which is the technical term for "cave formations", and refers to all secondary mineral deposits in caves. The most common speleothem-forming mineral is calcite (CaCO3 - calcium carbonate), the same mineral in limestone, which is the host rock for almost all caves on Earth. Speleothem composed of calcium carbonate is given the compositional rock name travertine. Some travertine forms at the surface, at hot springs or cold springs. Cave travertine forms in many specific ways, and genetic rock names have been established for the many known varieties (e.g., dripstone, flowstone, helictites, coralloids, shelfstone, rimstone, etc.).
The upright, wrinkled structures depicted above are well-developed examples of rimstone (rimstone dams), a less common variety of speleothem. Rimstone forms along the downstream margins of overflowing cave pools and has a wavy to highly convoluted shape in plan view. Calcium carbonate precipitation occurs along the margins of overflowing pools, which raises the level of the rimstone dam, which raises the water level of the pool. Through time, rimstones can become respectably tall.
The photos in this album were taken in boreal summer 2008. The cave closed in 2008 or 2009 when a cell phone company (Bluegrass) bought the entire hill of Prewitts Knob to prevent competition from other cell phone companies. The hill now has cell phone towers.
Locality: Prewitts Knob, ~2 air miles southwest of Cave City, northwestern Barren County, southwest-central Kentucky, USA (37° 06' 36.27" North latitude, 85° 58' 26.12" West longitude)
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