TRIPLE-QUANTUM AL-27 AND NA-23 MAS NMR-STUDY OF AMPHIBOLES

Triple-quantum magic-angle spinning (MAS) enhances the resolution of A l-27 and Na-23 NMR spectra of amphiboles, although the structural comp lexity of these compact materials can limit the efficiency of the meth od in comparison with its performance with molecular sieves. Two alumi nium environments are resolved in fluor-edenite, unequivocally demonst rating the presence of some long-range Si-Al disorder. Na-23 multi-qua ntum (MQ)-MAS of hydro-sodian-magnesiocummingtonite (HSMC) at two temp eratures demonstrates that a phase transition affects mainly site A. M Q-MAS allows the direct determination of the number of distinct sites with their quadrupolar parameters and isotropic chemical shifts. The t echnique is very useful for the simulation of MAS spectra.