Crystallographic Analysis of the Garnet Structure Type: Symmetry in the Structural Anatomy

Resumo

The crystallographic analysis of the garnet structure type (Al₂Ca₃(SiO₄)₃, Ia3d symmetry) establishes the determining role of the [AlCa₆Si₆] cation group with the local symmetry \(\bar 3\)in the structure formation. The glide planes of three directions coherently assemble these groups. High structural stability (three not symmetry-fixed coordinates per 80 atoms, the fundamental volume V*~17 ų) promotes the occurrence of various atomic compositions in it. The relation with the β-W structure type and the structure of menezesite mineral is shown.