ABSTRACT: Mineral assemblages stable according to Gibbs phase rule can be shown, on the diagrams having axes such as P/T, log f/(i by the Schrein.emak.ers method,. These diagrams may be too complex on the basis of `the number of the components and the degreees of freedom in the system. A computer programme in BASIC language is developed in order to .solve such kind of complex systems which can be solved in. very long times with small calculators. This programme was adopted for the IBM-PC because of .the wide distributions of these computers, öne natural sample which was studied by the Scheinemakers method, is resolved by the proposed programme in order to show the application of programme. It is possible to obtain all the parameters of the system to be .solved by this computer programme `without any additional calculations.