Composition,Structure, and Conditions of Formation of Fluorine-Bearing Sodalite: Experimental Evidence |
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Authors: | E N Gramenitskii A R Kotel’nikov T I Shchekina O V Yakubovich V N Devyatova E S Zubkov N I Suk M F Vigasina Z A Kotel’nikova |
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Institution: | 1.Faculty of Geology,Moscow State University,Moscow,Russia;2.Institute of Experimental Mineralogy,Russian Academy of Sciences,Chernogolovka,Russia;3.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Fluoro-sodalite was synthesized for the first time at temperatures of 400–800°C and H2O pressures of 1–2 kbar in the Si–Al–Na–H–O–F system. X-ray diffraction and infrared spectroscopic investigations showed that fluorine is incorporated in the sodalite structure as anionic octahedral groups, AlF6]3–, the number of which can vary from 0 to 1. Correspondingly, the end-members of the F-sodalite series are Na7(H2O)8Si5Al7O24] and Na8(AlF6)(H2O)4Si7Al5O24]. Depending on the composition of the system, F-sodalite associates at 500–650°C with nepheline, albite, cryolite, and villiaumite, which are joined by analcime below 500°C and aluminosilicate melt above 650°C. Fluorine-bearing sulfate–chlorine-sodalite was found for the first time in a pegmatite sample from the Lovozero massif. The highest fraction of the fluorine end-member in natural sodalite is 0.2. The incorporation of F into the sodalite structure requires much more energy compared with Cl– and SO 4 2- , because it is accompanied by a structural rearrangement and a transition from tetrahedral Al to octahedral Al. |
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