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The crystal structures of aluminosilicate-sodalites: X-ray diffraction studies and computer modelling

Published online by Cambridge University Press:  05 July 2018

B. Beagley ,
C. M. B. Henderson  and
D. Taylor
B. Beagley
Affiliation:
Department of Chemistry, UMIST, PO Box 88, Manchester M60 1QD
C. M. B. Henderson
Affiliation:
Department of Geology, The University, Manchester M13 9PL
D. Taylor
Affiliation:
Department of Geology, The University, Manchester M13 9PL
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Abstract

X-ray powder methods have been used to study the room-temperature structures of the synthetic sodalites: Li8(Al6Si6O24)Cl2, K7.6Na0.4(Al6Si6O24)Cl2, and Na8(Al6Si6O24)I2. Natural sodalite was also studied and the atomic coordinates show satisfactory agreement with those determined from the single-crystal data of Löns and Schulz (1967). The LiCl- and KCl- as well as the NaCl-sodalites refined in the expected sodalite space group P3n, but the NaI-sodalite fitted 13m better. The resulting structural data reveal shortcomings in the previous computer models for sodalite structures and an improved computer modelling procedure is devised which successfully predicts atomic coordinates, starting from the experimental a value and an estimate of the cationanion distance. The method incorporates the experimental result that the average T-O distance (T = Al, Si) throughout the samples is ∼ 1.678 Å, and Si-O and Al-O are set at 1.618 and 1.738 Å, respectively. Although T-O remains little changed throughout the samples, the data confirm the inverse relationship between ∠ T-O-T and the tetrahedron tilt angle ϕ, in which ∠ T-O-T approaches ∼ 160° as ϕ → 0° and the sodalite cage becomes fully expanded.

Type
Research Article
Information
Mineralogical Magazine , Volume 46 , Issue 341 , December 1982 , pp. 459 - 464
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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Footnotes

*

Present address: 15 Leigh Road, Congleton, Cheshire CW12 2EG.

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