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- Skogby, Henrik, et al.
(författare)
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Short-range order in tourmaline : A vibrational spectroscopic approach to elbaite
- 2012
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Ingår i: Physics and chemistry of minerals. - : Springer Science and Business Media LLC. - 0342-1791 .- 1432-2021. ; 39:10, s. 811-816
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Tidskriftsartikel (refereegranskat)abstract
- Polarized Fourier-transform infrared and Raman spectra were acquired on an elbaite sample previously characterized by electron- and ion microprobe analysis, X-ray diffraction and structure refinement. Spectra from the two vibrational spectroscopy techniques reveal a close similarity in the OH-stretching region, with three main absorption bands strongly polarized in the c-axis direction. By means of bond-valence theory arguments, the observed OH bands are interpreted and assigned to specific local cation arrangements around the O1 (≡W) and O3 (≡V) anion sites. In combination with the relatively simple composition of the studied sample, bond-valence constraints are used to identify stable anion-cation arrangements, which permit the occurrence of short-range ordering to be assessed. Evidence for nearly complete short-range order at the O1 site, with the stable arrangements Y(LiAlAl) 0. 6- W(OH) 0. 6 and Y(LiLiAl) 0. 4- W(F) 0. 4, are presented. These two local arrangements can be further expanded to obtain the larger ordered clusters [ W(OH)- Y(LiAl 2)- V(OH) 3- Z(Al) 6] 0. 6 and [ W(F)- Y(Li 2Al)- V(OH) 3- Z(Al) 6] 0. 4.
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