Minerals melt over wide range of temperature.We generally show ternary equilibria on triangular diagrams. Ternary systems involve three components.We typically show binary equilibria on temperature-composition diagrams. Binary systems involve two chemical components.We typically depict them on pressure-temperature phase diagrams. Unary systems, contain only one component.There are many different kinds of phase diagrams. We depict phase equilibria on phase diagrams.To simplify analysis and broaden applications, petrologists often study model systems involving only one or a few components.Thermodynamics deals with chemical systems, which are defined by the chemical components that make up everything in the system. The Laws of Thermodynamics govern phase equilibria.Unstable equilibrium means that chemical reactions are occurring. Metastable equilibrium means chemical energy is not minimized but no reactions are occurring. Stable equilibrium means chemical energy is at a minimum. Minerals and mineral assemblages may be at stable, metastable, and unstable equilibrium.Phase equilibria involve chemical reactions when one or more phases react to form different phases.The term phase refers to any compositionally and physically distinctive substance.8.0 Examples of crystallization paths for Fo-An-Qz melts
