A three-component triangular graph that is used to show how metamorphic mineral assemblages vary as a function of rock composition within one metamorphic facies. The three components are: A’ = (Al₂O₃) + Fe₂O₃) – (Na₂ + K₂O + CaO); K = (K₂O); F = (FeO + MgO + MnO). See also acf diagram.

http://www.tulane.edu/~sanelson/eens212/triangular_plots_metamophic_petrology.htm Describes triangular plots in metamorphic petrology.