QUARTZ DISSOLUTION - THEORY OF ROUGH AND SMOOTH SURFACES

The mathematics of step motion are developed for quartz dissolution and compared with rough-face behavior using two different models. According to these models, bonds are broken sequentially and interconversion of doubly and singly attached silica tetrahedra provides for surface diffusion. Rate equations applicable to smooth-face dissolution are derived and shown to agree with observations. The model predicts small but important (approximately 6 kJ/mol) differences in activation energy between smooth and rough faces, and roughly an order of magnitude range in pre-exponential constants. It further shows an almost insignificant energy can have profound effects on the crystal surface, including enhanced dissolution rate anisotropy, organization of the surface into steps, and straightening of steps.