CRYSTAL-STRUCTURE OF CU2HGSNS4, A SYNTHETIC ANALOG OF THE MINERAL VELIKITE

The crystal structure of Cu2HgSnS4, a synthetic analogue of the minera l velikite of the stannite group, was redetermined by the Rietveld met hod (WIRIET, Version 3.3). The parameters of the tetragonal unit cell are (a = 5.5749(6) and c = 10.882(1) Angstrom; Z = 2; and sp. gr. I (4 ) over bar. In calculations, the Pearson VII function (6FWHM) and atom ic scattering factors for neutral atoms were used. The asymmetry was r efined at 2 theta < 60 degrees. A simultaneous refinement of the profi le and structural parameters in the isotropic approximation resulted i n R-p = 3.09, R-wp = 3.95, R-B = 1.84, s = 1.19. and D-WD = 1.56, The structures of the various stannite-group minerals are compared. The se quence of the values of the isotropic thermal parameters of different atoms characteristic of the stannite-group minerals is also valid for synthetic velikite studied: B(Cu(2)) > B(Cu(1)) > B(Hg) > B(Sn) > B(S) .