Effects of melt viscosity and silica activity on the rate and mechanism of quartz dissolution in melts of the CMAS and CAS systems

The dissolution rate of quartz in melts of the CMAS and CAS systems at 1,600°C and 1.5 GPa is a function of both the silica activity of the melt and its viscosity. In melts with low silica activity quartz dissolves more quickly than in higher aSiO₂ melts regardless of viscosity. For melts with equal aSiO₂, dissolution is faster in the low viscosity melt. Quartz dissolution is controlled by interface kinetics in three of the four melts used in this study for times much greater than predicted by the model of Zhang et al. (in Contrib Mineral Petrol 102:492–513 1989). One melt which was previously shown to adhere to the predicted behaviour at lower temperature shows a significant activation time at higher temperature. All the dissolution data indicate that there are likely to be three distinct domains of dissolution behaviour, although the details of why a particular melt falls in any one domain require further study. Although the current database is small, the relationship between quartz solubility and the dissolution constant indicate that solubility may be a useful parameter for predicting dissolution rates, particularly if silica activity and melt viscosity are also known.