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.