Crystal Chemistry of Iron in Non-Metamict Chevkinite-(Ce): Valence State and Site Occupation Proportions

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Abstract

The ideal formula for chevkinite can be expressed as A4BC2D2Si4O22. It is important to determine the valence state and site occupation proportions for Fe among the B, C, and D octahedral sites as it may help to identify different species in the chevkinite group. Non-metamict chevkinite-(Ce) from Mianxi alkali feldspar-granite, Sichuan Province, China, was investigated using Mössbauer spectroscopy. The Fe3+/ΣFe ratio was 39.2%. A significant increase of Fe3+occured during metamictization and annealing for chevkinite-group minerals. In metamict samples Fe tended to lower coordination. According to the correlation between bond length and isomer shift (IS), the quadrupole doublets with IS = 1.10 and 0.94 mm·s-1can be assigned to Fe2+in the B and C octahedral sites, respectively. Based on the correlation between octahedral distortion and quadrupole splitting (QS), the quadrupole doublets with QS = 0.86 and 0.77 mm·s-1can be assigned to Fe3+in the C and D sites, respectively. The simplified formula can be revised as: Ce4Fe2+(Ti, Fe2+, Fe3+)2(Ti, Fe3+)2Si4(O, OH)22. It indicated that the non-metamict chevkinite-(Ce) belonged to Fe2+end member of the chevkinite group because Fe2+was the predominant component in the B site. © 2007 The Chinese Society of Rare Earths.

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Yang, Z., Li, H., Liu, M., & Franz, P. (2007). Crystal Chemistry of Iron in Non-Metamict Chevkinite-(Ce): Valence State and Site Occupation Proportions. Journal of Rare Earths, 25(2), 238–242. https://doi.org/10.1016/S1002-0721(07)60080-5

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