S-K-EDGE AND L-EDGE X-RAY-ABSORPTION SPECTROSCOPY OF METAL SULFIDES AND SULFATES - APPLICATIONS IN MINERALOGY AND GEOCHEMISTRY

S K- and Ledge XANES spectra of pyrrhotite (Fe1-xS), pyrite (FeS2), th e thiospinels carrollite (CuCo2S4 and linnaeite (Co3S4), and Mg, Ca, S r and Ba sulfates have been obtained using synchrotron radiation. The spectra of these metal sulfides are interpreted based on qualitative m olecular orbital (MO) - energy-band models, and indicate that the meta l 3d crystal-field band below the conduction band minimum has signific ant S 3s- and 3p-like density of states (DOS), because of strong parti cipation of the metal 3d electrons in the bonding of the metals with s ulfur. The S K- and L-edge spectra of sulfates are interpreted using M O theory. The S K- and L-edges shift to higher energy by about 10 eV f rom sulfides (S-2-) to sulfur (S-0), sulfite (S4+) and sulfates (S6+), providing a powerful and independent technique for the determination of oxidation state of sulfur. For semiconducting metal sulfides, the S K- and L-edges shift linearly to higher energy by 2-3 eV with increas e in the energy band gap E(g)), and curvilinearly to lower energy with increase in reflectivity.