K-Rich Mordenite from Late Miocene Rhyolitic Tuffs, Island of Samos, Greece

G. Pe-Piper1 and P. Tsolis-Katagas2
1 Department of Geology, Saint Mary's University Halifax, Nova Scotia B3H 3C3, Canada
2 Department of Geology, University of Patras, Patras 261 110, Greece

Abstract: Mordenite occurs in hydrothermally altered rhyolitic volcanic rocks at the margin of a Late Miocene lake basin on the island of Samos, Greece. The mordenite was identified by its X-ray powder diffraction pattern and appearance in scanning electron micrographs. Electron microprobe analyses show high Si, Ca, and K, low Na, and high balance errors. The b cell dimension is consistent with a high Si/(Al + Si) ratio, and the balance errors are apparently due to Na deficiency. The missing Na was estimated from the amount required to give (Si + Al) = 48 and yielded analyses comparable with X-ray fluorescence analyses of samples predominantly of mordenite. Even after this correction, the mordenite had a low Na:K ratio compared with most analyses reported in the literature. The peculiar chemistry of the mordenite may have resulted from a high-temperature metasomatic origin as a result of basaltic volcanism at the basin margin and characterized by hydrothermal circulation of alkaline lake water rich in K.

Key Words: Hydrothermal alteration • Mordenite • Potassium • Rhyolitic tuff • Volcanic ash • X-ray powder diffraction • Zeolite

Clays and Clay Minerals; June 1991 v. 39; no. 3; p. 239-247; DOI: 10.1346/CCMN.1991.0390303
© 1991, The Clay Minerals Society
Clay Minerals Society (www.clays.org)