A multinuclear magnetic resonance examination of the mineral grandidierite. Identification of a 27Al resonance from a well-defined AlO5 site.

11B, 27Al and 29Si magic angle spinning NMR results are reported for the boroaluminosilicate mineral grandidierite (Mg, Fe)Al3SiBO9. Three distinct aluminium sites are identified, two AlO6 and one AlO5. Despite overlap of the centrebands from these sites the use of three magnetic fields (9.4, 11.7 and 14.1 T) allows unambiguous values for the isotropic chemical shift (delta iso), quadrupolar coupling constant (Cq) and quadrupolar asymmetry parameter (eta) to be deduced for each site. The NMR spectrum from the AlO5 site is simulated with parameters Cq = 8.7 +/- 0.1 MHz, eta = 0.95 +/- 0.05 and delta iso = 41 +/- 1 ppm which are compared to values from other well-defined AlO5 units.