THE OXIDATION STATE OF COPPER AND COBALT IN CARROLLITE, CuCo2S4

Using X-ray absorption spectroscopy (XAS) at the Cu L-2,L-3 and Co L-2,L-3 edges, we demonstrate that the valence state of copper in the thiospinel carrollite (CuCo2S4) is Cu+ with a d count of Cu d(9.8). The Co has a d count of d(6.4), so that the highly covalent mineral has an electronic formula of Cu1.2+(Co2.4+)(2)(S1.5-)(4). There is half a hole per atom in the S 3p band (per unit formula); the Co L-2,L-3 XAS indicates a covalent low-spin electronic structure. These data dispel the notion of the presence of Cu2+ in carrollite.