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Citation

Schr?der C, Wan M, Butler I, Tait A, Peiffer S & McCammon C (2020) Identification of mackinawite and constraints on its electronic configuration using M?ssbauer spectroscopy. Minerals, 10 (12), Art. No.: 1090. https://doi.org/10.3390/min10121090

Abstract
The Fe(II) monosulfide mineral mackinawite (FeS) is an important phase in low temperature iron and sulfur cycles, yet it is challenging to characterize since it often occurs in X-ray amorphous or nanoparticulate forms and is extremely sensitive to oxidation. Moreover, the electronic configuration of iron in mackinawite is still under debate. M?ssbauer spectroscopy has the potential to distinguish mackinawite from other FeS phases and provide clarity on the electronic configuration, but conflicting results have been reported. We therefore conducted a M?ssbauer study at 5 K of five samples of mackinawite synthesized through different pathways. Samples show two different M?ssbauer patterns: a singlet that remains unsplit at all temperatures studied, a sextet with hyperfine magnetic field of 27(1) T at 5 K, or both. Our results suggest that the singlet corresponds to stoichiometric mackinawite (FeS), while the sextet corresponds to mackinawite with excess S (FeS1+x). Both phases show center shifts near 0.5 mm/s at 5 K. Coupled with observations from the literature, our data support non-zero magnetic moments on iron atoms in both phases, with strong itinerant spin fluctuations in stoichiometric FeS. Our results provide a clear approach for the identification of mackinawite in both laboratory and natural environments.

Keywords
mackinawite; iron sulfide; lepidocrocite; polysulfide; M?ssbauer spectroscopy; electronic configuration; magnetic hyperfine field; quadrupole splitting; Debye model

Journal
Minerals: Volume 10, Issue 12

• Published version