Solubility of natural fluorite at 25°C

The solubility products of two samples of natural fluorite from Rosiclare, Ill., and from Madoc, Ontario, were determined at 25°C by analyses of calcium and fluoride in sodium perchlorate solutions of varying ionic strength over a period of 3 years. Calcium concentrations were analyzed by atomic absorption spectrophotometry, fluoride concentrations were measured colorimetrically, and fluoride activities were measured using a specific ion electrode. The solubility products at the end of 3 years were determined by extrapolation to zero ionic strength. The final solubility product was found to be 10^-10.58±0.17.