Abstract
Diagrams relating physical properties to chemical composition are familiar to all mineralogists. An exhaustive list of citations to such diagrams would be impossible here, but would include such books as Troeger (1956) and Winchell (1951), and a great many shorter articles such as those of Sriramadas (1957), and Kennedy (1947). With only a few exceptions (as Ford, 1915), such charts show the physical properties such as one or more refractive indices, lattice constants, melting, inversion, and decomposition temperatures, specific gravity, etc., by means of contour lines drawn over diagrams in which the main coordinates are determined by chemical composition. Yet the commonest use of these charts is probably for determining composition from the physical measurements. The usual arrangement is clearly best if there are more physical parameters than chemical ones—but that condition is not necessarily satisfied, especially if physical parameters are limited to those that can be conveniently measured. An important example in which exchange of the dependent and the independent variables may be useful is the garnet system, where at least five chemical components should be determined, but the conveniently measured physical properties are only refractive index n, lattice constant, a, and specific gravity G.
