General Review of Phenomena and Processes

Abstract

In Part 1, the crystal structure was treated initially as an infinite, regular, threedimensionalarray of atoms arranged on intersecting lattices. Although this mathematical concept underlay the entire discussion of the physical and chemical properties, it was necessary to abandon the concept of strict regularity to permit description of substitutional and positional disorder. Furthermore it was necessary to consider termination of the crystal structure at surfaces, and to consider atomic displacements caused by strain between domains of different chemical composition. In this fourth part of the book, deviations from strict regularity will be treated more systematically. For each type of deviation a phenomenological description will be given followed whenever possible by a theoretical interpretation. Unfortunately not all the atomic processes responsible for the macroscopic effects have been detected by experimental methods, and some theoretical interpretations are plausible rather than verifiable. Thus it is not surprising that the literature is extremely confused, and that most ideas are still controversial. Nevertheless it is essential for mineralogists and geologists to master the experimental data and the hypotheses sinceactual processes are governed not by equilibrium thermodynamics but by local kinetics.