noun
: a salt Fe 2 (SO 4 ) 3 that is found in nature as the hydrated minerals coquimbite and quenstedtite and is also obtained synthetically (as by oxidation of ferrous sulfate) in the white anhydrous form and that is used chiefly in making iron alums, in pickling metals, as a mordant in dyeing, and as a coagulant in treating industrial wastes