Solid state ²⁹Si NMR examination of the 2:1 ribbon magnesium silicates, sepiolite and palygorskite

The results of a ²⁹Si NMR study of the 2:1 magnesium ribbon silicates, sepiolite and palygorskite are presented. Separate resonances between −92 and −98 ppm for the three and two types, respectively, of silica units across the ribbons are observed. This provides information on factors other than tetrahedral aluminium substitution which can affect the Q³ chemical shift. Also observed is a Q² SiOH resonance from crystal defects or edges. The structural changes which occur at the various stages of dehydration have been studied. Finally, some interesting observations on ²⁹Si relaxation and cross-polarization dynamics are presented.