Greigite (Fe<sub>3</sub>S<sub>4</sub>) is thermodynamically stable: Implications for its terrestrial and planetary occurrence.
basic_science · Level V
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- Record sourced from PubMed, PMID 33139534.
- Also identified by DOI 10.1073/pnas.2017312117 and PMC identifier 7682356.
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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 Fe<sub>3</sub>S<sub>4</sub> 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 Fe<sub>3</sub>S<sub>4</sub> 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.