The discussion presented by Miyazaki does not dispute the contention of Carlson (1999) that the best available values for the factors that control the intergranular diffusion of Al will not allow Ostwald ripening to govern size distributions of crystals larger than a fraction of a micrometer. Instead, it raises objections to previous descriptions of the diffusion-controlled growth of porphyroblasts during metamorphism. Those objections are based upon a diffusional scenario and a corresponding set of equations that are, unfortunately, inapplicable to porphyroblast crystallization. The discussion relies upon a metallurgical model for the growth of precipitates from a single-phase matrix with continuously...

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