The Crystal Structure and Chemical Composition of Cumengéite

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

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: cumengéite • crystal structure

Mineralogical Magazine; March 1986 v. 50; no. 355; p. 157-162; DOI: 10.1180/minmag.1986.050.355.21
© 1986, The Mineralogical Society
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