Mineralogical characterization of paulingite from Vinaricka Hora, Czech Republic

Universitat Wien, Institut fur Mineralogie und Kristallographie, Vienna, Austria

A sample of the zeolite paulingite from the locality Vinaricka Hora was investigated by means of chemical, thermal, powder and single crystal X-ray methods. The fully transparent, colourless to pale yellow crystals exhibit the form {110} and occur together with phillipsite. The chemical composition is (Ca (sub 2.57) K (sub 2.28) Ba (sub 1.39) Na (sub 0.38) ) (Al (sub 11.55) Si (sub 30.59) O ₈₄ ).27H ₂ O, Z = 16 with minor amounts of Mg (<0.05), Sr (<0.13), Mn (<0.01), and Fe (<0.04). The chemical differences from previously described paulingites are a high Ba-content, a lower Si/(Al+Fe) ratio of 2.64, and a reduced water-content. The calculated density is 2.098 g cm (super -3) , and the observed refractive index is 1.482(2). The dehydration behaviour is characterized by a main weight loss from 24-190 degrees C (-11.2 wt.%, congruent to 21H ₂ O) and a minor weight loss from 190-390 degrees C (-3.1 wt.%, congruent to 6H ₂ O). The rehydration capability was proven up to 150 degrees C. The dehydration process during the main weight loss is accompanied by a reduction of the cell volume of 11%. The refined lattice parameters of the X-ray powder data are a = 35.1231(5) Aa and a = 33.7485(8) Aa of an untreated and a dehydrated sample, respectively. A breakdown of the paulingite structure can be observed while the remaining water content decomposes. The single crystal X-ray refinement of this chemically different sample material derived three main cation positions, which are inside a so called paulingite or pi -cage (Ca), between 8-rings of neighbouring pi -cages (Ba), and in the centre of the non-planar 8-rings of the gamma -cage (K). Further partially occupied cation positions (Ca,Na) were located in the planar 8-rings of the alpha - and gamma -cages. No positions within the double 8-membered rings were detected. The water is localized around the main cation positions and in three clusters of partially occupied sites.

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				E. PASSAGLIA, A. F. GUALTIERI, and E. MARCHI The crystal chemistry of paulingite European Journal of Mineralogy, February 1, 2001; 13(1): 113 - 119. [Abstract] [Full Text] [PDF]