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The crystal structure and chemical composition of cumengéite

Published online by Cambridge University Press:  05 July 2018

F. C. Hawthorne  and
L. A. Groat
F. C. Hawthorne
Affiliation:
Department of Earth Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2
L. A. Groat
Affiliation:
Department of Earth Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2
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Abstract

The crystal structure of cumengéite, Pb21Cu20Cl42(OH)40, tetragonal, a= 15.065(2), c= 24.436(5) Å, V = 5546(2) Å3, space group I4/mmm, Z = 2, has been solved by direct methods and refined by least-squares to an R index of 7.1 % for 1158 observed (I > 2.5σ I) reflections. The cumengéite structure shows a very diverse range of cation coordinations. There are five distinct Pb sites with the following coordination polyhedra: octahedron, square antiprism, augmented trigonal prism, a very distorted biaugmented trigonal prism and a fairly regular biaugmented trigonal prism, the latter being only half-occupied; there are two distinct Cu sites with octahedral and square pyramidal coordination respectively. The coordination polyhedra share elements to form prominent columns or rods of polyhedra parallel to the c-axis and centred on the 4-fold axes of the unit cell. These rods form a body-centred array, and link by sharing elements of their coordination polyhedra.

Keywords

cumengéitecrystal structure
Type
Crystal Structures
Information
Mineralogical Magazine , Volume 50 , Issue 355 , March 1986 , pp. 157 - 162
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1986

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