X-ray single-crystal structure refinement of NH4-exchanged heulandite at 100 K
Yang, Ping; Armbruster, Thomas
European Journal of Mineralogy Volume 10 Number 3 (1998), p. 461 - 472
published: Jun 22, 1998
manuscript accepted: Dec 17, 1997
manuscript received: Aug 23, 1997
ArtNo. ESP147051003006, Price: 29.00 €
Abstract Heulandite single crystals from Nasik (India) were treated four weeks at 423 K in 2M NaCl solution. Subsequently, the resulting Na-exchanged form was kept two months at 373 K in 2M NH4Cl solution until all crystals were NH4-exchanged. The NH4 concentration in heulandite was also confirmed by nitrogen specific electron microprobe analysis. The crystal structure of completely NH4-exchanged heulandite, (NH4)8.8Al8.79Si27.25O72 ·16 H2O, space group C2/m, [a = 17.738(4), b = 17.974(5), c = 7.416(2) Å, ß = 115.91 (2)°] was studied by single-crystal X-ray diffraction at 100 K. The structure was refined on the basis of Fobs by least-square methods to R = 3.78 % and Rw = 4.96 %. By comparison with previously studied Na-, K-, Rb-, and Cs-exchanged heulandite three NH4 sites and eleven partially occupied H2O positions were determined. H positions of two NH4 groups were located and refined. In contrast to K, NH4 shows only a low population in the regular B channel but prefers the distorted C channel and pockets in the large A channel. IR-powder spectra revealed two well defined NH4 characteristic absorptions v3 at 3134 and v4 at 1400 cm-1 which are not significantly different to those reported for free NH4.