High-temperature crystal chemistry of georgbokiite

Phase transformations and thermal deformations in a new mineral georgbokiite, Cu5O2(SeO3)(2)Cl-2, were studied by the X-ray diffraction method. It is shown that anisotropy of thermal expansion of georgbokiite crystals is explained most satisfactorily by the presence of oxocentered [O2Cu5] chains parallel to the c-axis of the structure. These chains consist of [OCu4]-tetrahedra sharing alternatively either their vertices or edges.