The results of a HRTEM and electron diffraction investigation of a Cu- and Ag-rich cosalite, pairs of satellite reflections at Gp ± ~ 1 8* and Gp ± ~ 1 8[1̄40]* in addition to the strong Bragg reflections of the underlying average structure. The superlattice corresponds to a compositional and displacive modulation G ± qpnm where qpnm is the primary modulation vector 1 8*. 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  cosalite.
- Electron diffraction