²⁷ Al and ²⁹ Si mass NMR spectroscopy of glasses in the system anorthite-diopside-forsterite Available to Purchase

²⁷Al and ²⁹Si mass nmr spectroscopy of glasses in the system anorthite-diopside-forsterite indicates that, within the accuracy of the technique, all Si and A1 are tetrahedrally coordinated to oxygen and that most, if not all, of the A1 is in fully polymerized (Q⁴) sites. Estimates of the average Si-O bond length and average ∠Si-O-T (T = Si, Al) bond angle determined from empirical correlations of ²⁹Si chemical shift with bond length and angle indicate that these parameters vary from 1.62 Å and 134° for anorthite glass to 1.64 Å and 129° for Di₉₀Fo₁₀ glass. ²⁹Si peak maxima and breadths for glasses quenched from above the liquidus are nearly the same as those for glasses quenched from at or below the liquidus, but are slightly more shielded and broader. Model calculations based on the ²⁷Al peak maxima indicate that the abundance of Q⁴ sites in glasses along the join An-Di is approximately equal to that of a mechanical mixture of An and Di, whereas glasses along the join Cats-Di (data from Kirkpatrick et al., 1986a) contain more Q⁴ sites than expected for a mechanical mixture of Cats and Di. The models also indicate that the average polymerization of the non-Q⁴ sites is approximately Q² along the An-Di join and approximately Q¹⁷ along the Cats-Di join.