Calcite is the chief mineral in limestone, where it is generally in the form of small, broken fragments of fossil shells. Large, well-developed crystals are generally found in veins, commonly associated with faults. Numerous quarries throughout the State contain various nodules and geodes with calcite crystals. The Lexington Quarry Company in Nicholasville and the Caldwell Stone Company in Danville have discovered numerous scalenohedral calcite crystals along veins in the quarries. Vein calcite is usually associated with fluorite, barite, galena, and sphalerite.
Calcite often appears as twinned crystals.
Aragonite usually occurs as radiating crystals and is commonly found in reniform, columnar, and stalactitic forms. Travertine, often called cave onyx, has properties similar to calcite. It is usually a shade of yellow or brown, and exhibits banding because of intermittent deposition and iron oxide impurities. Travertine is redeposited calcium carbonate. The best known deposits in Kentucky are in caves near the Mammoth Cave region.