Cation ordering is often one of the most efficient ways a mineral can adapt to changing temperature or chemical composition. Disorder of distinct species across different crystallographic sites at high temperature provides significant entropic stabilisation of mineral phases relative to low-temperature ordered structures. For example, the calcite-aragonite phase boundary shows a significant curvature at high temperature due to disorder of CO3 groups within the calcite structure, associated with an orientation order-disorder phase transition (Redfern et al. 1989a). This leads to an increased stability of calcite with respect to aragonite over that predicted by a simple Clausius-Clapeyron extrapolation...

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