A method is described for the analysis of phosphorus in geological samples involving the decomposition of the sample with hydrofluoric acid in a quartz tube and the measurement of phosphate ion concentration using an ion chromatograph (Dionex 10) with an anion separator column (Wescan anion 269-001). The detection limit is between 0.05-0.5% P2O5in the original sample. Multiple analyses of eight U.S.G.S. standard rocks yielded a relative standard deviation range between 2.37-16.67%. In excess of 15 samples can be analyzed in an 8 hour day.