Abstract
Multiple-quantum (MQ) and satellite-transition (ST) magic-angle spinning (MAS) are two very similar techniques used to obtain high-resolution or "isotropic" NMR spectra of half-integer quadrupolar nuclei. In a variety of materials it is observed that some STMAS peaks are very broad compared with the corresponding MQMAS peaks, sometimes so broad that they are unobservable. We present ¹⁷O (I = 5/2) NMR spectra of two materials, chondrodite (2Mg₂SiO₄.Mg(OH)₂) and clinohumite (4Mg₂SiO₄.Mg(OH)₂), exhibiting this phenomenon and show that the cause is motional broadening arising from the combined effects of molecular reorientation, the quadrupolar interaction and MAS.