Structural and thermodynamic properties of water related defects in a-quartz

We have investigated the atomic geometries and thermodynamic properties of water related defects in a-quartz using first-principles calculation. We confirm that the (OH)4 group is thermodynamically most stable and aggregates to form platelets in the form of microcracks with hydrolysed surfaces. We also examine other forms of defects which can be accessible out of equilibrium at high temperature. Finally, we discuss the consequences of our results for the hydrolytic weakening of a-quartz.