Shape modification of mineral inclusions in diamond: thermodynamic and kinetic considerations

Abstract

The study of mineral inclusions in diamonds is attracting increasing interest among the scientific community of mineralogists and petrologists. A question that has recently been addressed is whether the shape of solid inclusions is immutable once trapped in the diamond or it can evolve over time until it manifests an equilibrium form. In this paper, we approach this topic by means of thermodynamic and kinetic considerations. The concept of equilibrium shape is revisited by inserting the Gibbs–Wulff theorem into a new perspective to fit the context of a mineral inclusion. We then demonstrate that it is currently not possible to determine the equilibrium shape of a mineral inclusion in a diamond, due to the large number of calculations that need to be performed. Successively, kinetic considerations on the formation of the equilibrium shape are made. It is shown that the shape evolution of an inclusion requires a significant amount of mass transfer at constant volume and the data currently at our disposal do not allow the estimation of the time needed to reach the equilibrium shape.