NMR spectra of moganite and chalcedony

29 Si MAS NMR, 29 Si { 1 H} CP MAS NMR and 1 H MAS NMR spectra of the water-containing microcrystalline silica varieties chalcedony, moganite and three intermediate samples are reported. The 29 Si MAS NMR spectra give evidence that, unlike quartz, the silicon atoms occupy two symmetrically different sites in moganite. The 1 H MAS NMR spectra show signals of molecular water and four different species of silanol groups