Effect of crystal chemistry and cation ordering on cleavage processes of dioctahedral micas: petrogenetic implications

Knowledge of the atomic arrangement of the topmost surface of micas is basic for the understanding of a large number of surface phenomena and interacting processes on the Earth's crust. Crystal structure of micas at the surface shows relaxation and reconstruction phenomena such as variation of coordination number for the interlayer cation and compositional variation from the composition of the bulk. These evidences support the hypothesis that small interlayer cations cluster at the cleavage plane and that a lack of homogeneity of the layers constituting the mica structure may produce preferential cleavage locations.