Abstract
Synthetic Fe3S4 is cubic, a0 = 9.90 Å, space group Fd3m, Z = 8. The parameter u of sulfur positions in 32e site is estimated as 3/8, i. e. it has an ideal structure. Fe3S4 was decomposed to tetragonal or hexagonal FeS and free S at below or above 190 °C under hydrothermal conditions. The transition between Fe3S4 and FeS seems to depend closely on their structures.