SOLVALC: An interactive graphics program package for calculating the ternary feldspar solvus and for two-feldspar geothermometry

The program SOLVCALC is a user-friendly graphic interface software for calculating the ternary feldspar solvus and the equilibrium temperature of coexisting natural ternary feldspar pairs. Twelve solvus isotherms (with or without tielines) and twelve thermometric tielines can be plotted on each screen. The zoom and move functions greatly reduce any physical limitations of the screen itself. Six different thermodynamic models for ternary feldspar and one user-defined model are incorporated into this program for both solvus calculations and thermometry. An activity matching algorithm is used for the solvus calculations. For the geothermometric calculations, an algorithm is used to search for the most concordant temperature by adjusting the feldspar compositions within selected uncertainty. SOLVCALC can be used as both a research and teaching tool for comparing different models as well as for development of new ternary feldspar models. The program runs on PC-compatible computers with DOS 3.1 or later version and a VGA graphic card. A copy of SOLVCALC 1.0 is available from the authors by request.