Rietveld refinement study of pyrite crystals

Rietveld refinement was performed for two samples prepared from natural pyrite (a polymorph of iron disulphide or iron persulphide, FeS2) single crystals originating from Navajun (Spain) and from Ural Mts. (Russia). The present refinements provide the following crystallographic data: a = 5.41784(2) and 5.41819(2) Å, x = 0.3848(1) and 0.3840(1) for the above-mentioned crystals, respectively. They are comparable with those of several crystals from other geological deposits, reported in literature. The obtained diffraction results indicate an off-stoichiometry with a higher sulphur content in the sample from Ural. The last observation is qualitatively supported by the results of X-ray photoelectron spectroscopy. The crystallographic data are discussed on the basis of earlier literature information on composition and structure reported for synthetic bulk and thin-layered pyrite.