THE CRYSTAL STRUCTURE OF OWENSITE, (Ba,Pb)6(Cu,Fe,Ni)25S27, A NEW MEMBER OF THE DJERFISHERITE GROUP

JAN T. SZYMANSKI
Mineral Sciences Laboratories, CANMET, Natural Resources Canada, 555 Booth Street, Ottawa, Ontario K1A 0G1

Abstract

The crystal structure of the new mineral species owensite, (Ba,Pb)6(Cu,Fe,Ni)25S27, is cubic, a 10.349(1) Å, space group Pm3m. Nine S atoms bond to each (Ba,Pb) atom. The unit cell contains a single (Cu,Fe,Ni) atom that is octahedrally coordinated by S; the other twenty-four (Cu,Fe) atoms are tetrahedrally coordinated. The structure is analogous to that of djerfisherite, K6Na(Fe,Ni,Cu)24S26Cl, but it contains no monovalent ions. The K sites in djerfisherite are here occupied by (Ba,Pb) atoms; the Na site is occupied by one of the (Cu,Fe,Ni) atoms, whereas the Cl site is occupied by a S atom. The structure was solved and refined to an R index of 5.2% for MoK data to 2 = 100 . The bond lengths and angles are all within the expected limits: Ba-S between 3.132(2) and 3.300(5) Å, (Cu,Fe)-S between 2.302(3) and 2.356(2) Å [tetrahedral], or 2.501(5) Å [octahedral]. The Pb atom replaces the Ba atom within the coordination S cage, but is disordered and displaced from the Ba atom position as a result of the presence of the 6s2 Pb electron pair. Four disordered Pb satellite positions exist, all 0.38 Å from the Ba position, and in a square with a side of 0.31 Å.

Keywords: owensite, barium copper-iron sulfide, structure refinement, atomic ratios, disordered lead, djerfisherite-group mineral.