New data on minerals with the GIS framework-type structure: gismondine-Sr from the Bellerberg volcano, Germany, and amicite and Ba-rich gismondine from the Hatrurim Complex, Israel

Abstract Gismondine-Sr, recently discovered in the Hatrurim Complex in Israel, has been recognised in a xenolith sample from the Bellerberg volcano in Germany. The empirical crystal-chemical formula indicates elevated K content: (Sr1.74Ca1.05Ba0.09K1.56Na0.49)Σ4.93[Al7.98Si8.06O32]⋅9.62H2O. Additionally, Ba-rich gismondine and amicite have been found in the low-temperature mineral association of the pyrometamorphic rock from the Hatrurim Complex. The Raman spectra of the studied zeolites and the crystal structure of gismondine-Sr from the second occurrence are presented. A review of zeolites with GIS framework-type structure leads to the following conclusions: (1) garronite-Na and gobbinsite are equivalent and constitute a solid solution with garronite-Ca; (2) gismondine-Ca, -Sr, and amicite belong to one mineral series; (3) two zeolites series with different R-factors (defined as Si/(Si+Al+Fe)) can be distinguished within GIS topology: the garronite series (R > 0.6) including garronite-Ca and gobbinsite, with general formula (MyD0.5(x–y))[AlxSi(16–x)O32]⋅nH2O, where M and D refer to monovalent and divalent cations, respectively; and the gismondine series, including amicite, gismondine-Sr and gismondine-Ca, with R ≈ 0.5, and the general formula (MyD0.5(8–y))[Al8Si8O32]⋅nH2O. The Raman band between 475 cm–1 and 485 cm–1 is distinctive for the garronite series, whereas the band around 460 cm–1 is characteristic of the gismondine series. On the basis of these findings, a revision of GIS zeolites nomenclature is suggested.