Constraining 17O and 27Al NMR spectra of high-pressure crystals and glasses: New data for jadeite, pyrope, grossular, and mullite

The 17 O NMR spectra of glasses quenched from melts at high pressure are often difficult to interpret due to overlapping peaks and lack of crystalline model compounds. High-pressure aluminosilicate glasses often contain significant amounts of [5] Al and [6] Al, thus these high-pressure glasses must contain oxygen bonded to high-coordinated aluminum. The 17 O NMR parameters for the minerals jadeite, pyrope, grossular, and mullite are presented to assist interpretation of glass spectra and to help test quantum chemical calculations. The 17 O NMR parameters for jadeite and grossular support previous peak assignments of oxygen bonded to Si and high-coordinated Al in high-pressure glasses as well as quantum chemical calculations. The oxygen tricluster in mullite is very similar to the previously observed tricluster in grossite (CaAl 4 O 7 ) and suspected triclusters in glasses. We also present 27 Al NMR spectra for pyrope, grossular, and mullite.