We are most grateful for the opportunity to prepare this paper as a special way of expressing our admiration and appreciation for the productive career and lasting contributions of Professor J. W. Christian. The subject we have selected here for review, although rather narrow in a sense, constitutes a realm of phase transformations that highlights the dynamic interplay among structure, thermodynamics, kinetics, properties, and practical implications-the very spectrum of teaching and research epitomized by the life's work of Professor Christian.