Phase transformations and thermal deformations in a new mineral georgbokiite, Cu₅O₂(SeO₃)₂Cl₂, 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.