Chemical analyses of sixteen lithium-aluminium micas are presented along with their optical, physical, and X-ray data. Compositional variation, substitution relations in structural positions, and octahedral occupancy are discussed. The 2M~ structural types are found to crystallize in volatile-rich low-temperature environments whereas the I M polytypes occur in comparatively volatilepoor and hig...

Luminescence data for 6 manganese doped langbeinites, Aj B2 + (S04)3 , are reported. They are consistent with octahedral symmetry of the impurity center (substitutional in B site), although for the host lattice the B site is known to show three-fold axial (distorted octahedral) symmetry only. In accordance with previous conclusions from EPR data the luminescence parameters indicate structural r...

The possible lower symmetries (subgroups) of the A2BX4 structure (space-group symmetry D4& ) due to rigid octahedral tiltings at phase transitions are investigated. The method for obtaining subgroups determined by reducible representations (i.e., coupled order parameters) is described. This method depends upon subgroup information for irreducible representations (i.e., single uncoupled order pa...