| Summary: | In this work, the chemical structural characterization of the erionite-type zeolite from Agua Prieta, Sonora, México, was performed on both pristine and Na, Ca, and Mg exchanged samples in order to identify the various modifications due to cation exchange. The samples investigated were those that showed the best behaviour of CO<sub>2</sub> and CH<sub>4</sub> adsorption at zero coverage levels and the higher values of surface area reported in our previous studies. According to the crystal-chemical formula (Na<sub>3.44</sub>K<sub>1.96</sub>Mg<sub>0.63</sub>Ca<sub>0.62</sub>)[Al<sub>8.21</sub>Si<sub>27.79</sub>O<sub>71.85</sub>]·29.63H<sub>2</sub>O, the pristine sample has been classified as erionite-Na. Morphological FE-SEM investigation performed on both pristine (ERIN) and Na-exchanged samples (ERINa3) showed a similar range of fiber diameters (27–37 nm). The chemical analyses of the ion-exchanged samples evidenced the upload of Ca and Mg following ion exchange with Na. Rietveld analysis results allowed the identification of the chemical structural modification caused by the ion exchange process, occurring mainly at the Ca1 site.
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