Dislocations and feldspar dissolution
Murphy, William M.
European Journal of Mineralogy Volume 1 Number 3 (1989), p. 315 - 326
published: Jul 27, 1989
manuscript accepted: Feb 24, 1989
manuscript received: Aug 29, 1988
ArtNo. ESP147050103002, Price: 29.00 €
Abstract Field and laboratory data and theoretical analyses reported in the literature suggest that the rate of dissolution of minerals depends on the density of dislocations in the crystal structure. However, new data for the reaction of sanidine at 95 °C in dilute aqueous solutions at pH ≈ 3 show no significant differences in the rates or stoichiometry of mass release for undeformed and experimentally deformed samples with low and high dislocation densities, respectively. Stoichiometric and thermodynamic analyses of the aqueous solution data suggest periods of initial preferential release of K relative to SiO2, followed by stoichiometric release of K and SiO2, and then incongruent precipitation of a silica-bearing phase. However, the Na to K release ratio is greater than the stoichiometric ratio in the sanidine. Preferential secondary mineral precipitation at deformation features leads to Al:SiO2 ratios that are lower in solutions in experiments with deformed sanidine than in the undeformed sanidine experiments. Scanning electron microscopy shows development of etch pits in both deformed and undeformed specimens, but the relation between etch pits and dislocations is equivocal.