Szomolnokite

A common alteration product of iron sulphides (pyrite, marcasite, pyrrhotite). Forms a complete solid solution with kieserite (Talla and Wildner, 2019). End-member szomolnokite, FeSO4·H2O, is monoclinic, and synthetic CuSO4·H2O is triclinic. The cell-parameter refinements of (Fe,Cu)SO4·H2O compounds show a reduction in symmetry from monoclinic to triclinic beyond 20 mol% Cu. By Mössbauer spectroscopy significant ordering involving the cations can be observed only in members of the solid solution with more than 20 mol% Cu. Site ordering is characterized by a preference of ferrous iron for the less distorted site (Giester et al., 1994).