Molten system Na₃AlF₆ − SiO₂ was examined by high temperature NMR. Further characterizations of the samples prepared by Rapid Solidification Processing (RSP) technique and by spontaneous solidification were performed by X–ray diffraction and solid state NMR. The high solubility of SiO₂ in molten cryolite and the immiscibility phenomenon were observed. Using thermogravimetric analysis, weight losses were detected, which could be attributed to the formation of the volatile products. The results of the present study are the evidence that SiO₂ reacts with molten Na₃AlF₆ under the formation of the volatile SiF₄, non − volatile NaF, and alumino−silicate AlSi₃O₈⁻ species. NMR spectroscopy coupled with diffraction−based methods was proved as a promising approach to obtain information about the structure and chemistry of this rather complex system.