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GEOREF RECORD

Flexibility and distortion of the framework of natrolite; crystal structures of ion-exchanged natrolites

Werner H. Baur, Dethard Kassner, Choon-Hee Kim and Norbert H. W. Sieber
Flexibility and distortion of the framework of natrolite; crystal structures of ion-exchanged natrolites
European Journal of Mineralogy (December 1990) 2 (6): 761-769

Abstract

The crystal structure of the Li-exchanged form of natrolite, Li (sub 1.6) Na (sub 0.4) Al (sub 2) Si (sub 3) O (sub 10) . 2H (sub 2) 0, was refined based on 568 F (sub obs) , R = 0.071. For comparison the structure of a natrolite, Na (sub 2) Al (sub 2) Si (sub 3) O (sub 10) . 2H (sub 2) O, was also refined (1278 F (sub obs) , R = 0.040). The diffraction data collected for K-natrolite were of insufficient quality, therefore a computer simulation of the K-form was based on the experimentally determined cell edges and space group. The mean rotation angles psi of the chains (composed of 4 = 1 secondary building units) relative to the a and b cell axes are observed to be 25 degrees (Li-compound), 24 degrees (Na-compound) and 18 degrees (K-compound). A detailed comparison shows that only the transformation to K-natrolite conforms approximately to the currently widely accepted model of rotating chains. Surprisingly the Li-form instead achieves the observed shortened cell constants a and b by a distortion of the chain itself, the rotation is only a secondary effect. Both cation exchanged forms display also shortened c-axes, which is an indication that the chains of 4 = 1 units are tilted and twisted within themselves. It is most likely that the angle of the hinge at the oxygen atom O2 is in Na-natrolite already at the lower attainable limit beyond which it would become energetically unfavorable, and thus it cannot be reduced any further when the Na-natrolite is transformed by ion-exchange into a Li-natrolite.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 2
Serial Issue: 6
Title: Flexibility and distortion of the framework of natrolite; crystal structures of ion-exchanged natrolites
Affiliation: Johann Wolfgang Goethe-Univ., Inst. Kristallogr. Mineral., Frankfurt a.M., Federal Republic of Germany
Pages: 761-769
Published: 199012
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 17
Accession Number: 1994-008251
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables, 8 anals.
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany
Update Code: 199404
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