Kinetics of dissolution of mechanically comminuted rock-forming oxides and silicates—II. Deformation and dissolution of oxides and silicates in the laboratory and at the Earth's surface

Abstract

Comparison of the patterns of fracture under tensile stress, indentation, and scratching of periclase. quartz, and corundum indicates that the properties relevant to dissolution of rock-forming oxides and of rock-forming non-layer silicates should be changed by mechanical comminution in essentially the same way as those of quartz. The changes are accomplished by brittle fracture under the tensile component of the stress field, which does not generate subsurface damage, and by microplastic behavior under local stresses with high net compressive and shear components, which does. Mechanical comminution should therefore affect the apparent rates of dissolution (rates calculated with respect to the initial interface area) of rock-forming oxides and of rock-forming non-layer silicates in essentially the same way in which it affects the apparent rate of dissolution of quartz. This is supported by the available evidence on the effect of dry grinding on the kinetics of dissolution of feldspars, pyroxenes, and olivines in aqueous solutions. Different effects of mechanical comminution on solubilities and dissolution rate constants can be related to certain measured or calculated properties of the considered minerals. Notably, the effect of grain size on the dissolution rate constant can be rigorously related to the Kelvin effect. The available evidence on the mechanical comminution at the bases of dry-based glaciers in highgradient segments of streams, in certain high-energy coastal and epeiric environments, and in sandy deserts indicates that such mechanical comminution should significantly affect the simultaneous or subsequent dissolution of the comminuted material.