Barrerite from Alaska was investigated by 29Si, 27Al and 23Na MAS NMR both in its untreated (as-found) and heated forms. The chemical shift of the 29Si NMR lines of the natural phase revealed the presence of three different Si(nAl) configurations. The 27Al NMR signal of the natural phase, positioned in the region of tetrahedrally coordinated Al, becomes more shielded with increasing temperature, in agreement with the changes of the Al-O-Si bond angles caused by the distortion of the framework observed by means of X-ray diffraction (Alberti & Vezzalini, 1978). Changes in the 27Al NMR line-width were also correlated to dehydration at high temperature. 27Al 2D triple-quantum MAS NMR spectra were recorded on natural and dehydrated barrerite. In neither case the five tetrahedral sites could be differentiated by the MQMAS technique. 23Na MAS spectra were preliminarily collected on the untreated barrerite and on the sample heated at 450°C and the shift of the resonance line towards higher fields in the heated phase was interpreted as a consequence of the heating process and of the increased coordination number.

You do not currently have access to this article.