Thermodynamics of ordering and mixing in plagioclase feldspars: atomistic modelling in favour of Landau theory

Plagioclase feldspars are key components of terrestrial planets and deriving their phase diagram activity–composition relations has been the subject many studies. Three main approaches have used for thermodynamic modelling behaviour plagioclase feldspars, all three disagree in terms magnitude relative importance mixing energies ordering energies. The present study uses Monte Carlo simulations based on classical atomistic to provide independent constraints over anorthite its solid solution with albite. Unsurprisingly, Al-avoidance plays a role. competition between first-neighbour second-neighbour interactions is highlighted, providing simple explanations high degree short-range order macroscopically disordered plagioclase. properties obtained this support strong non-ideality, negative enthalpy temperature-dependent entropy. Ordering consistent studies using Landau theory. Unfortunately, form equations hindered parametrisation full model from albite anorthite, even though formalism remains simple. Reasons, perspectives, implications ternary discussed.