<unk> (II) sulfate is the chemical compound with the formula<unk> SO4.  This salt exists as a series of compounds that differ in their degree of hydration.  The anhydrous form is a pale green or gray-white powder, whereas the pentahydrate, the most commonly encountered salt, is bright blue.  This hydrated<unk>  sulfate occurs in nature as the mineral called chalcanthite. Archaic names for<unk> (II) sulfate are "blue vitriol" and "bluestone".
Copper
Iron
Biotin
Thiol
Heme
Organophosphorus
Cobalt
Famine