Crystal-chemistry and synchrotron Rietveld refinement of two different clinoptilolites from volcanoclastites of North-Western Sardinia
Cappelletti, Piergiulio; Langella, Alessio; Cruciani, Giuseppe
European Journal of Mineralogy Volume 11 Number 6 (1999), p. 1051 - 1060
published: Nov 29, 1999
manuscript accepted: Jul 6, 1999
manuscript received: Dec 16, 1998
ArtNo. ESP147051106014, Price: 29.00 €
Abstract Two clinoptilolites from genetically different volcanoclastic formations have been studied. Both deposits are located in the Logudoro region (North-Western Sardinia, Italy) within epiclastic and pyroclastic formations related to calcalkaline volcanic activity. Chemical characterization performed by electron microprobe analysis on both samples showed a quite similar composition ([Si/(Si+Al)] = 0.81÷0.82), with the exception of some extra-framework cations. In particular the epiclastic clinoptilolites turned out to be much higher in Mg content (0.72 vs. 0.26 a.f.u.) and considerably lower in K (1.10 vs. 2.37 a.f.u.) than the pyroclastic clinoptilolites. Previous investigations evidenced a different behaviour of the two clinoptilolite samples towards cation exchange processes and a substantial difference between the theoretical and experimental CEC. In this frame, Rietveld refinements based on synchrotron data allowed to define a different cationic population within the four exchangeable cation sites.