- © The Mineralogical Society Of America
Measurement of the rate of diffusion of hydrous species in anhydrous minerals has been a subject of growing interest for the last ten years. Hydrogen diffusion studies are of fundamental importance to estimate the rate of transfer of hydrous species in natural conditions but also to identify the nature of the reactions involved in the speciation of hydrogen in minerals. For low concentration hydrous point defects, spectroscopic techniques are usually not sufficient to fully determine the location of hydrogen in the mineral structure. In these cases, kinetics studies provide additional constraints on the number of different defects stored in the mineral and their specific reaction rates.
Numerous experimental data of hydrogen diffusion in minerals have now been published in the Earth Sciences literature. This review provides a digest to these data for a variety of minerals with a special focus on hydrogen in nominally anhydrous minerals. The review will not address the question of molecular water diffusion in minerals, melts or glasses. For a recent review of that question see for instance Doremus (2002). After a brief outline of basic diffusion concepts and methods of measurement, we summarize the main features of atomic diffusion linked to hydrogen isotope exchange and hydrogen reaction in minerals.
BASIC CONCEPTS OF DIFFUSION IN MINERALS
Atomic diffusion is defined as the transport of matter in response to a driving force, which can be a chemical potential gradient or a temperature gradient. Atomic diffusion induced by a thermal gradient is very limited in solid earth sciences whereas the occurrence of strong chemical gradients is much more frequent in minerals. Atoms move from one region to the other in order to equilibrate the chemical potentials μ and reduce the Gibbs free energy of the system. The disequilibrium induced by a chemical potential gradient (dμ/dx)i of a component i …