The crystal structure of gottardiite, a new natural zeolite
Alberti, Alberto; Vezzalini, Giovanna; Galli, Ermanno; Quartieri, Simona
published: Feb 22, 1996
manuscript accepted: Sep 7, 1995
manuscript received: Mar 22, 1995
ArtNo. ESP147050801008, Price: 29.00 €
Abstract Gottardiite is a new high-silica zeolite found in the Jurassic dolerites of Mt. Adamson (Victoria Land, Antarctica). Its unit-cell content is: Na2.5K0.2Mg3.1Ca4.9Al18.8Si117.2O272· 93 H2O. The mineral is orthorhombic with a = 13.698(2), b = 25.213(3), c = 22.660(2) Å, topological symmetry Fmmm and real symmetry Cmca. In the Fmmm symmetry there are oxygens on centres of symmetry, which cause energetically unfavourable T-O-T angles of 180°; in the Cmca symmetry the sets of 1̄̅, on which these oxygens lie, disappear. The topology of gottardiite, which has not been found in other natural zeolites, is the same as that of synthetic zeolite NU-87; the latter, however, is characterized by a monoclinic symmetry P21/c (a = 14.32, b = 22.38, c = 25.09 Å, β = 151.5°). The framework of gottardiite can|be described by the polyhedral units 5462 arid 54. These units developing along [0101 give rise to chains which, sharing edges with other analogous chains, form impermeable sheets parallel to (001). Each sheet is bonded to other analogous sheets through 4-rings of tetrahedra between, and parallel to the sheets. A 2-D channel system parallel to (001) is present in gottardiite. Straight 10-ring channels run parallel to , whereas 12-ring channels “snake” in the  direction. 10-ring and 12-ring channels are connected through 10-ring windows. The ion sites localized in the channels all have weak electron density and large distances (>2.7 Å) from framework oxygens. An enrichment in Al in the tetrahedra of 4-rings can be envisaged.