THE CRYSTAL-STRUCTURE OF GARNETS .1. THE RESIDUAL ELECTRON-DENSITY DISTRIBUTION IN PYROPE

The crystal structure of pyrope, Mg3Al2Si3O12, was refined by the. X-ray diffraction method with anharmonic thermal vibration considered, applying the Gram-Charlier series expansion up to the fourth-rank tensors (R = 0.015 for 688 reflexions). A positive electron density residue due to bonding electrons 0.7 eangstrom-3 in height was observed between the silicon and oxygen atoms. Crystal data: [Natural specimen from Parigi, Martiniana Po, Cuneo, Italy; Cubic garnet structure; Ia3dBAR; Z = 8; a(o) = 11.4582(6) angstrom; V = 1 504.35 angstrom3; D(x) = 3.560 g cm-3; mu = 11.88 cm-1; lambda(MoKalpha) = 0.71069 angstrom, F(000) = 1 600; T = 296 K].