1063-7745/05/5003- $26.00 © 2005 Pleiades Publishing, Inc. 0367 Crystallography Reports, Vol. 50, No. 3, 2005, pp. 367–373. Translated from Kristallografiya, Vol. 50, No. 3, 2005, pp. 411–417. Original Russian Text Copyright © 2005 by Zubkova, Pushcharovsky, Giester, Pekov, Turchkova, Chukanov, Tillmanns. INTRODUCTION Zorite Na 6 Ti(Ti,Nb) 4 (Si 6 O 17 ) 2 (O,OH) 5 × nH 2 O, where n ~ 11, is a typical representative of natural microporous heteropolyhedral-framework silicates having pronounced zeolite properties. Zorite was described as a new mineral from the famous Yubilei- naya pegmatite, a large hyperagpaitic pegmatite mined at Karnasurt Mountain of the Lovozero alkaline massif (Kola Peninsula, Russia) [1]. In the Yubileinaya pegma- tite, zorite involved in the late hydrothermal assem- blage is very abundant. This mineral is also present in several pegmatites at Karnasurt Mountain but has not been found anywhere else in the world. No known min- erals have structures analogous to the crystal structure of zorite, which is based on a mixed framework formed by xonotlite-like [Si 6 O 17 ] ribbons consisting of eight- membered tetrahedral rings. The ribbons are extended along the [001] direction and are linked to each other by columns of vertex-sharing (Ti,Nb)O 6 octahedra and isolated (Ti,Nb)O 5 half-octahedra. The framework includes two systems of zeolite channels running along the [010] (the minimum diameter is 4.3 Å) and [001] (the minimum diameter is 4.6 Å) directions. These channels are randomly occupied by Na atoms and H 2 O molecules. Sodium atoms occupy two nonequivalent positions and have, correspondingly, octahedral coordi- nation formed by four O atoms and two H 2 O molecules and sevenfold coordination formed by O atoms. According to [2], the polyhedral framework of zorite contains two types of rods parallel to the [010] direction. The rods of the first type contain tilting zig- zag columns of the (Ti,Nb)O 6 octahedra fastened by Si(1)O 4 tetrahedra. This structural fragment of zorite corresponds to the 7.238-Å period along the b axis and resembles those observed in nenadkevichite (Na,K) 2 - x [(Nb,Ti) 2 (Si 4 O 12 )(O,OH) 2 ] × 4H 2 O [3] and other minerals of the labuntsovite group. The rods of the second type are formed by TiO 5 half-octahedra and half-occupied Si(2)O 4 tetrahedra. If these tetrahedra were completely occupied, the adjacent Si(2)O 4 tetra- hedra along the [010] direction would be linked together by sharing faces. This fragment of the polyhe- dral framework, as well as the Na atoms and water mol- ecules located in the channels of the framework, is responsible for possible doubling of the period along the b axis. The disordered arrangement of this fragment results in the absence of periodicity along the a and c axes and is responsible for the OD character of the structure as a whole [2]. In 1996, the first data on the synthetic analog of zorite were published. This analog was called ETS-4 (Engelhard Titanium Silicate-4). The synthesis was car- ried out under hydrothermal conditions, and the prod- uct was obtained as thin intergrowths of two titanosili- cates, which are analogs of zorite (ETS-4) and “Ti- nenadkevichite” (korobitsynite, an orthorhombic Ti- dominant member of the labuntsovite group) [4, 5]. The Rietveld refinement of the ETS-4 structure confirmed its similarity to the zorite structure [6]. However, in contrast to zorite, both Ti atoms in ETS-4 have octahe- dral coordination. Later, the crystal structure of the Sr- exchanged form of ETS-4 was also studied by powder X-ray diffraction [7]. This structure was considered as a result of microintergrowth of four polymorphs, which STRUCTURE OF INORGANIC COMPOUNDS Crystal Structures of K- and Cs-Exchanged Forms of Zorite N. V. Zubkova*, D. Yu. Pushcharovsky*, G. Giester**, I. V. Pekov*, A. G. Turchkova*, N. V. Chukanov***, and E. Tillmanns** * Faculty of Geology, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia e-mail: dmitp@geol.msu.ru ** Institute of Mineralogy and Crystallography, Geocenter, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria *** Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia Received October 1, 2004 Abstract—The crystal structures of K- and Cs-exchanged forms of zorite were studied by X-ray diffraction and IR spectroscopy: K 4.75 Na 1.82 [Ti(Ti 0.79 Nb 0.20 ) 4 Si 12 O 34 (O,OH) 5.2 ] × 10.62 H 2 O (sp. gr. Cmmm, R = 0.0481 for 516 independent reflections) and Cs 4.34 Na 1.90 [Ti(Ti 0.80 Nb 0.18 ) 4 Si 12 O 34 (é,éç) 5 ] × 5.37 H 2 O (sp. gr. Cmmm, R = 0.0285 for 621 independent reflections). Both structures retain the mixed polyhedral framework of zorite: Na 6 Ti(Ti,Nb) 4 (Si 6 O 17 ) 2 (O,OH) 5 × nH 2 O, where n ~ 11. It is shown that the positions of the atoms located in the cavities of the frameworks of these compounds differ from those in the structures of zorite and its synthetic ana- logs. © 2005 Pleiades Publishing, Inc.