Atomistic simulation of mineral–melt trace-element partitioning

We discuss recent advances in computational approaches to trace-element incorporation in minerals and melts. It is crucial to take explicit account of the local structural environment of each ion in the solid and the change in this environment following the introduction of a foreign atom or atoms. Particular attention is paid to models using relaxation (strain) energies and solution energies, and the use of these different models for isovalent and heterovalent substitution in diopside and forsterite. Solution energies are also evaluated for pyrope and grossular garnets, and pyrope–grossular solid solutions. Unfavourable interactions between dodecahedral sites containing ions of the same size and connected by an intervening tetrahedron lead to larger solubilities of trace elements in the garnet solid solution than in either end member compound and to the failure of Goldschmidt’s first rule. Our final two examples are the partitioning behaviour of noble gases, which behave as ‘ions of zero charge’ and the direct calculation of high-temperature partition coefficients between CaO solid and melt via Monte Carlo simulations.