A method is described for the analysis of fluorine in geological samples involving the decomposition of the sample with phosphoric acid and the measurement of the fluoride ion concentration using an ion chromatograph. The detection limit is below 5 g F in the original sample. Multiple analyses of NBS-91 Opal Glass yielded a relative standard deviation of less than 2.5%. In excess of 30 samples can be analyzed in an 8 hour day. Potential interference from high carbon containing samples, such as oil shales, is discussed.