Fluorides are usually found in nature as constituents of soils, water, and the tissues of animals. Fluorite or fluorspar (CaF2), cryolite (Na3AlF6), apatite (3 Ca3 (PO4)2 CaF2) and sedimentary phosphate rocks are among the principle minerals containing fluorides found in nature. Traces of fluorides also occur in domestic water supplies in nature and also by induction in vegetation and animal feeds. From 0.5 ppm to 1.5 ppm of fluorides in drinking water is the range found to be beneficial in reducing the incidence of tooth decay in man. In animals, receiving abnormally elevated intakes of fluorides for a relatively short time or from sustained ingestion of small quantities over long periods, interference with normal life processes with resultant impaired performance or utility has been reported In industrial areas, fluorine as fluorides are present in varying amounts in the atmosphere. It is liberated by industrial processes which make use of high temperatures in the treatment of materials containing fluorine, either as a natural impurity or added as fluorspar for fluxing processes. The burning of coal by homes and industries liberates small quantities of fluorides into the atmosphere also. Residues of fluoride have been found on vegetation from these sources. Chronic fluorine poisoning (fluorosis) in animals may result from prolonged ingestion of fluorides. The symptoms of fluorosis depend on the level of intake, form of fluoride, duration of intake, age and nutritional status of the animals and their individual susceptibility.