Greigite (Fe ₃ S ₄ ) is thermodynamically stable: Implications for its terrestrial and planetary occurrence

Abstract

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe3S4 spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe–S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe3S4 in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.

Temperature-Dependent Reaction Pathways in FeS2: Reversibility and the Electrochemical Formation of Fe3S4

“…8,48−50 More recently, greigite been shown to be a thermodynamically stable Fe−S phase near ambient conditions. 51 To further validate the electrochemically formed Fe 3 S 4 , the Fe valence state was compared to other iron sulfides (FeS 2 and h-FeS) in XAS. As a result of the mixed Fe 2 + /3 + valence in the inverse-spinel Fe 3 S 4 structure, the formation of Fe 3 S 4 exhibits an average Fe valence >2 + .…”

“…Fe 3 S 4 is a less studied iron sulfide battery material, , but it is a well-studied iron sulfide in the field of geology for its role as an intermediate phase involved in pyrite formation on earth. , Greigite has been reported to form geologically from mackinawite (t-FeS) in the presence of excess sulfur and known to be an intermediate phase formed prior to pyrite FeS 2 formation under anoxic conditions (eq ). ,− More recently, greigite been shown to be a thermodynamically stable Fe–S phase near ambient conditions . To further validate the electrochemically formed Fe 3 S 4 , the Fe valence state was compared to other iron sulfides (FeS 2 and h-FeS) in XAS.…”

Co-reduction of Fe(III) and S0 drives Fe-S biomineral formation and phosphate mobilisation

“…Greigite is increasingly recognised as a common and stable phase in nature and as an important intermediate for pyrite formation (Subramani et al, 2020). We found the highest percentage of greigite at the intermediate pH of 7.2 (53 % of solid phase Fe).…”

Fe3S4 nanoparticles wrapped in a g-C3N4 matrix: an outstanding visible active Fenton catalysis and electrochemical sensing platform for lead and uranyl ions

“…In a recent study (September 2020), Tamilarasan Subramani et al at Arizona State University disproved the commonly held hypothesis that greigite is a metastable phase. 31 Moreover, to avoid the agglomeration tendency, the decoration of Fe 3 S 4 nanoparticles onto a carbonaceous framework is the ideal choice. [32][33][34][35] Therefore, in the future, we expect more research output while addressing the challenges in the synthesis and stabilization of thermodynamically stable Fe 3 S 4 nano-adsorbent materials.…”