Crystal structure-crystal chemistry relationships in the zeolites erionite and offretite

Abstract

The new mineral tscho rtnerite, ideally Ca 4 (K,Ca,Sr,Ba) 3 Cu 3 (OH) 8 [Si 12 Al 12 O 48 ]xH 2 O, x 20, occurs as well-formed cubes up to a maximum size of 0.15 mm in a Ca-rich xenolith at the Bellberg volcano near Mayen, Eifel, Germany. The light blue, transparent crystals are optically isotropic, n 1.504(2). Microprobe analysis (in weight percent) gave CaO 13.10, CuO 9.64, SrO 4.49, BaO 1.93, K 2 O 1.37, Fe 2 O 3 0.30, Al 2 O 3 25.21, SiO 2 30.25, H 2 O (calc. by difference) 13.71. The empirical formula based on 48 O atoms within the tetrahedral net is Ca 5.60 Sr 1.04 K 0.70 Ba 0.30 Cu 2.90 Fe 0.09 Al 11.85 Si 12.06 O 48 (OH) 8.44 14.01H 2 O. Tscho rtnerite is cubic, space group Fm3m [a 31.62(1) A