Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate is a salt with the formula FeSO₄. It is used medically to treat iron deficiency, and also for industrial applications. Known since ancient times as copperas and as green vitriol, the blue-green heptahydrate is the most common form of this material. All iron sulfates dissolve in water to give the same aquo complex [Fe(H₂O)₆]²⁺, which has octahedral molecular geometry and is paramagnetic.