• journal_title：American Mineralogist
• Contributor：Ramona Langner ; Michael Fechtelkord ; Alberto García ; Erika J. Palin ; Javier López-Solano
• Publisher：Mineralogical Society of America
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2012.3840
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：97
• issue：2-3
• firstpage：341
• section：Articles

The cationic ordering in the octahedral and tetrahedral sheets of Al-rich synthetic phlogopites with composition K(Mg_3−xAl_x)[Al_1+xSi_3−xO₁₀](OH)₂ (0.0 < x < 1.0) has been investigated using a combined approach of Monte Carlo simulations based on the “J formalism” (Bosenick et al. 2001; Warren et al. 2001) and ¹H, ²⁹Si MAS and {¹H} → ²⁹Si CPMAS/HETCOR solid-state NMR spectroscopic experiments. Our results are compatible with the well-established Loewenstein’s rule of Al-Al avoidance in the tetrahedral sheets, but the Si/^IVAl and Mg/^VIAl distributions show a tendency to segregation of the excess Al atoms, and we observe a preference for ^VIAl and ^IVAl to occupy directly neighbored octahedral and tetrahedral sites. As a result the structure is separated into clusters of original phlogopite composition {K(Mg₃)[AlSi₃O₁₀](OH)₂} and clusters of “eastonite” composition {K(Mg₂Al)[Al₂Si₂O₁₀](OH)₂} that encompass a whole T-O-T layer package, although Al is solved in the phlogopite structure homogeneously on a macroscopic level.