¹Tamilarasan Subramani,¹Kristina Lilova,¹Mykola Abramchuk,¹Kurt D. Leinenweber,¹Alexandra Navrotsky
Proceedings of the National Academy of Sciences of the United States of America Link to Article [DOI:
https://doi.org/10.1073/pnas.2017312117]
¹School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Tempe, AZ 85281

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.