Crystal chemistry of elpidite from Khan Bogdo (Mongolia) and its K- and Rb-exchanged forms
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Crystal Chemistry of Elpidite from Khan Bogdo (Mongolia) and Its K and RbExchanged Forms A. A. Grigor’evaa, N. V. Zubkovaa, I. V. Pekova, U. Kolitschb, c, D. Yu. Pushcharovskya, M. F. Vigasinaa, G. Giesterc, T. Dordevic' c, E. Tillmannsc, and N. V. Chukanovd a
Faculty of Geology, Moscow State University, Moscow, 119992 Russia email: [email protected] b Department of Mineralogy and Petrography, Museum of Natural History of Vienna, Burgring 7, A1010 Vienna, Austria c Institute of Mineralogy and Crystallography, University of Vienna, Althanstr. 14, A1090 Vienna, Austria d Institute of Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia Received April 4, 2011
Abstract—Elpidite Na2ZrSi6O15 ⋅ 3H2O [space group Pbcm, a = 7.1312(12), b = 14.6853(12), and c = 14.6349(15) Å] from Khan Bogdo (Mongolia) and its K and Rbexchanged forms K1.78Na0.16H0.06ZrSi6O15 ⋅ 0.85H2O [Cmce, a = 14.054(3), b = 14.308(3), and c = 14.553(3) Å] and Na1.58Rb0.2H0.22ZrSi6O15 · 2.69H2O [Pbcm, a = 7.1280(10), b = 14.644(3), and c = 14.642(3) Å] that were obtained by cation exchange at 90°C, as well as K1.84Na0.11H0.05ZrSi6O15 ⋅ 0.91H2O [Cmce, a = 14.037(3), b = 14.226(3), and c = 14.552(3) Å] and Rb1.78Na0.06H0.16ZrSi6O15 ⋅ 0.90H2O [Cmce, a = 14.2999(12), b = 14.4408(15), and c = 14.7690(12) Å], obtained at 150°C are studied by singlecrystal Xray diffraction and IR spectroscopy. The base of the struc tures is a heteropolyhedral Zr–Si–O framework whose cavities accommodate Na (K, Rb) cations and H2O molecules. DOI: 10.1134/S1063774511050117
INTRODUCTION Elpidite Na2ZrSi6O15 · 3H2O belongs to silicates with heteropolyhedral frameworks, which have received much attention in the last fifteen years due their wide application in chemical technologies as microporous zeolitic materials. Synthetic compounds of a similar structure are promising and in many cases are already used as ionites, highselectivity sorbents, catalyzers, ion conductors, etc. [1]. Microporous minerals with heteropolyhedral frameworks which are able to form deposits are of special interest as potential mineral resources. The most important of them are sodium zirconosilicates, namely, members of the evdi alite group and elpidite. It was found in a large number of experiments that under mild conditions (no higher than 150°C) ionexchange properties are not charac teristic of evdialites, whereas elpidite has the property of exchanging cations even at room temperature [2]. Indications that elpidite exhibits ionexchange prop erties in nature were noted in [3]. The largest accumu lations of elpidite, which are potentially of commer cial significance, are associated with complexes of raremetal alkaline granites. The most vivid examples of such deposits are large bodies of elpidite granites and their pegmatites at the Khan Bogdo and Khaldzan Buregteg massifs in Mongolia [4]. The structure of elpidite is based on a heteropoly hedral framework consisting of double Si6O
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