Freieslebenite

Freieslebenite was discovered in approximately 1773 in the Himmelsfurst mines of Freiberg, Saxony, Germany. The mineral was initially called Schilf-Glaserz; however, in 1845 it was given the current name Freieslebenite after the Mining Commissioner of Saxony, Johann Carl Freiesleben (1774–1846).

Structure

Freieslebenite is a superstructure of a PbS-type substructure. The crystal structure is monoclinic with a space group P2₁/a, with a = 7.518(1), b = 12.809(4), c = 5.940(1) Å, β = 92.25(1)° and Z = 4(Ito, 1973). Sb has a trigonal-pyramidal coordination of S atoms, this structure isolates the SbS3 pyramids from themselves. The Sb–S distances are 2.431, 2.453 and 2.480(4) Å. Six S atoms are coordinated with Pb in a distorted octahedral arrangement. The Pb–S distances range from 2.806 to 3.167(4) Å. Ag has three nearest S neighbors at the distances 2.522, 2.575 and 2.687(4) Å. The AgS3 group is almost planar. A fourth S atom is at a distance of 2.928(4) Å from Ag, the Ag–S being closely perpendicular to the AgS3 plane (Cascarano et al., 1987). The crystal structure of freieslebenite was determined by Wuensch and Nowacki in 1967. Wuensch and Nowacki determined the crystal structure of freieslebenite using three-dimensional counter data, systematic consideration of all possible arrangements permitted by the subcell-supercell relationship and the method of key shifts (Ito, 1973).