Quantitative Assessment of Reactive Surface Area of Phlogopite during Acid Dissolution

The reactive surface area of a dissolving sheet silicate, phlogopite, was quantitatively assessed in experiments performed in the fluid cell of an atomic force microscope at room temperature and pH values of 2 and 5.7. Additional assessment was provided by surface chemical analysis and electron diffraction. Dissolution rates of phlogopite {hk0} edges are in the range of 10$^{-10}$ moles per square meters per second, two orders of magnitude faster than bulk rates for this mineral. The basal {001} surfaces also show distinct reactivity, although it is short-lived before they become relatively inert. These basal surfaces are shown to leach, hydrate, and expand to an amorphous silica-enriched film.