An intermediate/mixed-valence S compound, as a mixture with pyrite/marcasite from Amelia mine, Wisconsin.
'UM1995-34-SO:Fe', a thiosulphate, is also present.
The phase may form homogenous, black-gray patchy areas, ca. 50 microns in size.
Many similar, mostly Fe-dominant unnamed species are known from carbonate-hosted Zn-Pb and other deposits; compare
viaeneite,
Unnamed (Pb Thiosulphate);
sidpietersite and
fassinaite;
Unnamed (Fe Subsulphite),
Unnamed (Fe Sulphite),
Unnamed (Zn Sulphite),
Unnamed (Fe Pyrosulphite),
Unnamed (Fe Sulphoxylane),
Unnamed (Fe Thiosulphate II). You can compare
Unnamed (Fe Oxysulphide), too.