Si-29 MAS NMR, Si-29 {H-1} CP MAS NMR and H-1 MAS NMR spectra of the w
ater-containing micro-crystalline silica varieties chalcedony, moganit
e.and three intermediate samples are reported. The Si-29 MAS NMR spect
ra give evidence that, unlike quartz, the silicon atoms occupy two sym
metrically different sites in moganite. The H-1 MAS NMR spectra show s
ignals of molecular water and four different species of silanol groups
.