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Mackinawite [Fe1+xS]
Structure Tetragonal
Space Group P4/nmm
(No. 129)
a=3.6735 Å,
c=5.0328 Å
Atomic Positional Parameters
Fe 2a 0.0000 0.0000 0.0000
S 2c 0.0000 0.5000 0.26023
Reference
AR Lennie, SAT Redfern, PF Schofield
and DJ Vaughan (1995) Mineralogical Magazine, 59, 677-683
Mineral Chemistry
Mackinawite is a metastable iron-sulphur phase important as a precursor to pyrite formation in sedimentary and hydrothermal systems. It is the first-formed iron sulphide phase following reaction of ferrous ions with sulphide ions. The crystal structure is simple, with iron coordinated tetrahedrally by sulphur. Sulphurs are in an asymmetric one-sided four-fold coordination with iron. Iron is in square-planar coordination with neighbouring irons.
The CHIME figure shows sulphur as yellow and iron as orange spheres.