Structure and properties of aluminosilicate garnets and katoite: an ab initio study

The structural properties of end-members of the aluminosilicate garnet fami ly (pyrope, grossular, spessartine and almandine) and of one hydrogarnet (k atoite) have been investigated as a function of applied pressure. The calcu lated static geometry, bulk modulus and its pressure derivative are in good agreement with available experimental data. The results of a systematic st udy of the effect of the size of the divalent cation on compressibility are presented. The bonding and dynamics of Mg in pyrope are investigated by us ing frozen phonon calculations. (C) 2000 Elsevier Science B.V. All rights r eserved.