Original paper
(010) disorder, partial Si,Al ordering, and Ca distribution in triclinic (C1) epistilbite
Yang, Ping; Armbruster, Thomas
European Journal of Mineralogy Volume 8 Number 2 (1996), p. 263 - 272
17 references
published: Apr 22, 1996
manuscript accepted: Oct 26, 1995
manuscript received: Jun 1, 1995
DOI: 10.1127/ejm/8/2/0263
Abstract
Abstract The crystal structure of epistilbite, Na0.3K0.2Ca2.7Al6.2Si17.9O48· 16 H2O, from Gibelsbach, Fiesch (Valais, Switzerland) was refined from X-ray single-crystal data at 100 K and 293 K in space group Cl (100 K: a = 9.051(3), b = 17.689(6), c = 10.152(7) Å, α = 89.93(4), ß =124.35(4), γ= 89.95(3)°; 293 K: a = 9.083(1), b = 17.738(3), c = 10.209(1) Å, α = 89.95(1), ß = 124.58(1), γ= 90.00(1)°). In contrast to previous studies where the space groups C2 or C2/m were assumed, reflection intensities clearly suggest triclinic symmetry. The reason for the symmetry lowering from monoclinic C2 to triclinic C1 is partial Si,Al ordering accompanied by a preferred distribution of the channel cations close to the underbonded oxygen atoms of the tetrahedral framework. The hitherto enigmatic occurrence of two domain variants (A, B) formed by different tetrahedral configurations could be modelled by (010) disorder caused by a local mirror plane.
Keywords
epistilbite • zeolite • Si,Al-ordering • disorder • crystal structure