Aspects of Feldspar Dissolution

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Abstract
The rate of sodium and potassium released from an alkali feldspar reacting with an aqueous solution varied with time. After an initial rapid exchange of alkalis for H+, dissolution rate decreased gradually, following in sequence, exponential, parabolic, and linear kinetics. Silicon was not released in the earlier stages but subsequently behaved very similarly to the alkalis. Aluminum behaved very similarly to the alkalis at the early stages but quickly reached saturation. Under an inert atmosphere, the pH of the solution was buffered at 8 to 10 after the initial sharp rise during the ion exchange stage. Dissolution occurred preferentially along crystal imperfections such as fractures, fluid inclusions, and grain boundaries rather than uniformly throughout the entire surface. The surface of a feldspar dissolved incongruently for the first few days of reaction but dissolved congruently thereafter. Clusters of precipitates occurred as discrete growths covering only small parts of the surface and were unlikely to retard dissolution.