The interest for the environmental, industrial and technological applications of Si-rich zeolites is very high. Among the large-pore zeolites, faujasite is one of the most exploited. The aim of this paper is to obtain detailed structural information on natural and NH4 -exchanged faujasite before using this zeolite for dealumination tests, targeting the realization of large single crystals of allsilica faujasite. As one of the most Si-rich natural samples, faujasite from Sasbach (Na13.64 K0.87 Mg10.46 Ca8.89 Sr0.34 (Al51.95 Si139.57 ) O384 ·272.29 H2 O; space group Fd-3 m; a = 24.6906(2) Å) was chosen for study. Single-crystal X-ray diffraction structural refinements of both natural and NH4 -exchanged samples are reported and discussed. In the natural faujasite sample, almost all the extraframework species could be located for the first time. In the NH4 -exchanged sample the ammonium and water molecule sites were located. Ammonium cations occupy two of the sites occupied by the extraframework species in the original mineral.