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 all-silica faujasite. As one of the most Si-rich natural samples, faujasite from Sasbach (Na13.64K0.87Mg10.46Ca8.89Sr0.34(Al51.95Si139.57)O384∙272.29 H2O; space group Fd-3m;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.

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