Thermodynamics of order-disorder in minerals: II. Symmetric formalism applied to solid solutions

摘要: The thermodynamics of order-disorder in mineral solid solutions are handled with symmetric formalism, whereby the is treated as a solution between an independent set end-members which range composition and states ordering phase can be represented. An n-component mineral, requiring s order parameters to represent state involves n + end-members. Symmetric formalism ideal mixing-on-sites regular-solution activity coefficients. It applied omphacite, orthopyroxene, ferromagnesian clinoamphibole, alkali feldspar. model for single parameter, successfully produces topology paired miscibility gaps tricritical points at their apices critical curve connecting them. Ferromagnesian orthopyroxene shown behave effectively all geologically relevant temperatures. Cummingtonite-grunerite slightly positively nonideal either two-site or three-site model. Na-K feldspars order-parameter coupling involving tetrahedral site occupancies show essential topologic relationships this system, only one binary interaction energy. power comes from simplicity its representation minerals flexibility few adjustable parameters.