P. Cappelletti et al., Crystal-chemistry and synchrotron Rietveld refinement of two different clinoptilolites from volcanoclastites of North-Western Sardinia, EUR J MINER, 11(6), 1999, pp. 1051-1060
Two clinoptilolites from genetically different volcanoclastic formations ha
ve been studied. Both deposits are located in the Logudoro region (North-We
stern 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 composi
tion ([Si/(Si+Al)] = 0.81 divided by 0.82), with the exception of some extr
a-framework cations. In particular the epiclastic clinoptilolites turned ou
t to be much higher in Mg content (0.72 vs. 0.26 a.f.u.) and considerably l
ower in K (1.10 vs. 2.37 a.f.u.) than the pyroclastic clinoptilolites.
Previous investigations evidenced a different behaviour of the two clinopti
lolite samples towards cation exchange processes and a substantial differen
ce between the theoretical and experimental CEC. In this frame, Rietveld re
finements based on synchrotron data allowed to define a different cationic
population within the four exchangeable cation sites.