Point Defects and Diffusion in Minerals

Abstract

Defects in minerals play a central role in the mechanics of many geochemical and geophysical phenomena. Prominent among these phenomena are processes whose rates are controlled by bulk diffusion or the coupling of bulk diffusion and other mechanisms. Among these are (1) the homogenization of zoned crystals, (2) alteration of the compositions of minerals, (3) order-disorder reaction, (4) resetting of radiometric ages and the formulation of closure temperatures, (5) isotopic equilibration, (6) plastic deformation of minerals, (7) formation of exsolution lamellae, and (8) growth and dissolution of minerals and related processes such as sintering. Largely due to the compositional complexity of geologic materials, progress in understanding the relationship between mineral point defect chemistry and diffusion in geologic materials has been rather limited. In fact, entitling this chapter “Point Defects and Diffusion in Olivine” would have required the omission of surprisingly little data. Before continuing, we refer the reader the texts of Lasaga and Kirkpatrick (1981) and Schmalzried (1981), and the references therein, for more detailed descriptions of point defect chemistry.