• journal_title：The Canadian Mineralogist
• Contributor：Bing Zhou ; Barbara L. Sherriff ; Francis Taulelle ; Gang Wu
• Publisher：Mineralogical Association of Canada
• Date：2003-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.41.4.891
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：41
• issue：4
• firstpage：891
• section：Articles

Zunyite [Al₁₃Si₅O₂₀(OH,F)₁₈Cl] possesses an unusual combination of an Al₁₃O₁₆(OH)₂₄ Keggin structure and a Si₅O₁₆ pentamer unit. We used ¹⁹F, ²⁷Al, ²⁹Si MAS and ²⁷Al MQMAS NMR spectroscopy of a series of samples with varying Al:Si and F:OH ratios to investigate the degree of atomic order in zunyite. The quadrupole coupling constant (C_Q) and asymmetry parameter (η) obtained from simulations of ²⁷Al MAS and MQMAS spectra were compared with those derived from the electric field gradients (EFG), which were calculated from an ab initio cluster quantum model using the program Gaussian 98W. This comparison led to unequivocal assignments for ²⁹Si, ²⁷Al and ¹⁹F MAS NMR peaks and showed that the number of Al substituting for Si(1) in the pentamer increases with Al content. The number of Al octahedra with one F atom increases with F content, whereas the number with two F atoms remains negligible, indicating that F preferentially occupies AlO₄OHF octahedra.