Triple-quantum Al-27 and Na-23 MAS NMR study of amphiboles

Triple-quantum magic-angle spinning (MAS) enhances the resolution of Al-27 and Na-23 NMR spectra of amphiboles, although the structural complexity of these compact materials can limit the efficiency of the method in comparison with its performance with molecular sieves. Two aluminium environments are resolved in fluor-edenite, unequivocally demonstrating the presence of some long-range Si-Al disorder. Na-23 multi-quantum (MQ)-MAS of hydro-sodian-magnesiocummingtonite (HSMC) at two temperatures demonstrates that a phase transition affects mainly site A. MQ-MAS allows the direct determination of the number of distinct sites with their quadrupolar parameters and isotropic chemical shifts. The technique is very useful for the simulation of MAS spectra.