Calcium can be quantitatively precipitated as sulfate in 90 per cent methanol solution. In contrast to sulfate separation methods which depend upon conversion of both calcium and magnesium sulfate with a solvent, in the method here described the calcium sulfate is formed in solution without attempting to convert all or even most of the magnesium to sulfate. The precipitated calcium sulfate is readily ignited and weighed as the anhydrous salt. By this method calcium can be accurately separated from a preponderant excess of magnesium and from a preponderant excess of magnesium and from small amounts of aluminum and iron, but not from other commonly associated elements such as strontium. The method is especially convenient for the rapid determination of calcium in magnesite and in technical grades of magnesium oxide. It is less satisfactory for the determination of high percentages of calcium, such as are found in limestone.