Epitaxy Governs the Location and Orientation of Nucleation in Metamorphic Rocks

Abstract Developing a full understanding of many geological and synthetic material processes, such as crustal metamorphism, mantle phase transformations, and alloy grain refinement requires knowledge of the way in which crystals nucleate within a multiphase crystalline matrix. Nevertheless, a common set of rules that predict the location and orientation of nuclei growth in crystalline reactions has not previously been described. By studying the orientation relationships in 12 natural parent–daughter pairs with varying symmetry, we illustrate that nucleation of crystalline phases in rocks can be rationalised by a model of epitaxy, in which the location and orientation of nuclei maximise coincident-site lattice bond interactions with a parental phase. We suggest that epitaxy is the default (lowest energy) nucleation pathway in natural mineral reactions, which has implications for the self-organisation of mineral systems, the kinetics of metamorphic reactions as well as the rheology of multiphase rocks. Broadly applied, our epitaxy model allows us to predict the microstructure of metamorphic rocks based solely on the lattice structure and chemistry of constituent phases.