Ferrous sulfate

Ferrous sulfate (FeSO₄) is an example of an ionic compound. It is found in various states of hydration (FeSO₄·H₂O, FeSO₄·4H₂O, FeSO₄·5H₂O, FeSO₄·7H₂O); the heptahydrate is also called green vitriol, copperas, or melanterite (a mineral that commonly occurs with pyrite). Ferrous sulfate has a blue-green color, monoclinic crystal strucutre, and is water-soluble. Its melting point is 64°C, and at 90°C it loses water of hydration to form the monohydrate, a white powder known as the mineral szomolnokite when it occurs naturally. Iron sulfate pentahydrate forms the mineral siderotil.

Ferrous sulfate is prepared commercially by oxidation of pyrite or by treating iron with sulfuric acid. It is used in the manufacture of inks, in wool dyeing as a mordant[?], and in water purification as a substitute for aluminum sulfate[?]. It can also be used to treat iron deficiency.