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HRTEM observations of structural and chemical modulations in cosalite and its relationship to the lillianite homologues

Published online by Cambridge University Press:  05 July 2018

A. Pring  and
B. Etschmann
A. Pring*
Affiliation:
Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, South Australia, 5000, Australia Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia
B. Etschmann
Affiliation:
Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, South Australia, 5000, Australia
*
*E-mail: [email protected]
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Abstract

The results of a HRTEM and electron diffraction investigation of a Cu- and Ag-rich cosalite, Cu1.2Ag0.9Pb6.7Bi8.2S20, from Ivigtut, Greenland, are presented. Electron diffraction patterns down [001] show pairs of satellite reflections at Gp±~1/8[140]* and Gp±~1/8[40]* in addition to the strong Bragg reflections of the underlying average structure. The superlattice corresponds to a compositional and displacive modulation G±qprim where qprim is the primary modulation vector 1/8[140]*. The superlattice is attributed to coupled Ag/Pb/Bi and Cu/□ ordering and associated structural relaxation. The HRTEM images show a complex moire texture due to the structural modulations. Cosalite from Ivigtut, Greenland, also forms coherent intergrowths with members of the lillianite–gustavite series (Pb3Bi2S6–PbAgBi3S6). A model for the intergrowth between the structures is presented based on sharing both S and Pb atoms in the PbS-like slabs in both structures along [010]cosalite.

Keywords

cosalitelillianiteHRTEMelectron diffractionIvigtutGreenland
Type
Research Article
Information
Mineralogical Magazine , Volume 66 , Issue 3 , June 2002 , pp. 451 - 458
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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