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Twinning in an orthorhombic aluminate sodalite, Ca8[Al12O24] (CrO4)2

Published online by Cambridge University Press:  05 July 2018

Ishmael Hassan
Ishmael Hassan*
Affiliation:
Department of Geology, Faculty of Science, University of Kuwait P.O. Box 5969, Safat, Kuwait 13060
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Abstract

Transmission electron microscopy (TEM) was used to study the aluminate sodalite, Ca8[Al12O24](CrO4)2. This aluminate sodalite has four polymorphs: one cubic, one modulated, one tetragonal, and an orthorhombic cell that arise from ordering of [Ca4·CrO4]6+ clusters that occur in the cages of the structure. The transition temperatures are 432, 453, and 610 K. The cell parameters for the orthorhombic phase, with the cubic cell parameter of a = b = c = 9.222 Å, are 3a × 2b × c. Transformation twins are formed at 432 K during the transition from the tetragonal to the orthorhombic phase. The twin plane is {110} in the cubic cell, and {320} in the orthorhombic cell.

Keywords

aluminate sodalitetwinningsodalite groupnoseanhaüynelazuriteTEMsuperstructures
Type
Mineralogy
Information
Mineralogical Magazine , Volume 60 , Issue 401 , August 1996 , pp. 617 - 622
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1996

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