Abstract
Natural jordanite from Binnatal, Switzerland is monoclinic, space group P21/m, with a = 8.918(1), b = 31,899(4), c = 8.462(1) Å and β = 117.79(1)°. The unit cell is approximately halved along both the a and c axes. Starting from the one-fourth substructure, the complete structure was solved by a kind of minimum residual method (the method of key shifts), and was refined by ordinary Fourier and least-squares methods (R = 7.0%).
The structure of jordanite is a deformed PbS-type structure. The unit cell contains 40 metal and 46 sulfur atom sites. The twelve independent metal sites are distributed on three layers at y ≈ 0.05, ≈ 0.15 and ≈ 0.25 (the mirror plane), with four metal sites, 3 Pb + As, on each layer. These metal layers are interleaved by sulfur layers; three additional S atoms are added to the third metal layer to form a metal-sulfur mixed layer. Some of the sites have statistical nature; one Pb site on the first layer is occupied by 0.50 Pb + 0.50 As, another Pb site on the third layer is occupied by 0.88 Pb. Thus, the unit-cell content is Pb27.8As12.0S45.8, with the ideal formula Pb28As12S46.
The fully occupied Pb atoms on the first, second and the third layers are coordinated with six (average Pb–S = 3.01 Å), seven (3.04 Å) and eight (3.08 Å) S atoms, respectively. The sulfur coordinations about the As atoms are ordinary trigonal pyramids with an average As–S = 2.25 Å. The AsS3 pyramids are isolated from each other (type I.c1 of the classification of Nowacki).
