Plotting a series of compositions in a triangular diagram in terms of molecular alumina, silica, and total alkalis will reveal any consistent trend in silica and total alkali variation such as might be expected by feldspar fractionation. A quadrilateral diagram in which the molecular alumina is plotted against soda/potash ratio can then be employed to show the variation in alkali ratio in whole rocks (and their feldspars) with changes in silica content and peralkalinity. Many of the pantellerites examined in this way appear to be on a quartz-feldspar crystallization path. Moreover, there is no strong indication that they have been simply derived from a trachyte parent by feldspar fractionation.