Nitrates, particularly potassium nitrate, are common in many of the caves in Kentucky and have historically been mined for saltpeter. The more famous of these cave nitrate deposits are located in the Carter Caves State Park System, Carter County, the Great Saltpeter Cave in Rockcastle County, the Big Sink Cave System in Pulaski County, and many of the caves associated with Mammoth Cave in Mammoth Cave National Park in Edmonson County. There are thousands of caves in Kentucky, many of which produced nitrates for the early settlers and for the Confederacy during the Civil War.
Nitrates are primarily potassium nitrates, which when mixed with chacoal and sulfur make black powder. Nitrates form from organic or biologic activity, and there are different forms of nitrates. Saltpeter caves are primarily inorganic nitrates that can be obtained and concentrated through various conversion processes using water, solution, filtration, large vats, and final precipitation. Guano caves are primarily organic bat guano. Once collected, these organic guanos are concentrated into nitrates through processes similar to that for inorganic nitrates (De Paepe and Hill, 1981).
Numerous sulfates occur in the New Albany black shale and on some coal beds or coal refuse piles. These sulfate minerals are secondary oxidation products, are humidity or water sensitive and include gypsum, jarosite, melanterite, copiapite, alunite, kalinite, pickeringite, and epsonite. Unusual uranium sulfates like Zippeite have also been identified. When forming, these sulfates experience crystal growth and large volumetric increases, which causes heaving or swelling of soils. Most of these sulfates form from the oxidation of pyrite and, can be considered a geologic hazard when encountered during construction activities. Detailed geologic engineering reports regarding foundation failures related to pyrite oxidation and sulfate expansion are discussed under the Hazards section of the KGS webpage and are available at KGS.
Foundation problems and pyrite oxidation in the Chattanooga Shale, Estill County, Kentucky