Crystal structure of a new Ca, Nb-representative of the labuntsovite group

The structures of monoclinic minerals of the labuntsovite group are based o n the zeolite-like framework formed by corrugated chains of Ti(Nb) octahedr a linked via shared vertices. The chains, in turn, are linked through four- membered silicon-oxygen rings and additional M-II octahedra, which are comp letely or partially filled with small divalent cations M2+ = Mn, Fe, Mg, an d Zn. The cavities of the framework are occupied by large alkali and alkali ne-earth cations and water molecules. Three types of extraframework cationi c positions (A(I), A(II), and A(III)) are clearly distinguished by their si ze and location in the structures of labuntsovite