NH₄Fe(SO₄)₂·12 H₂O, or NH₄[Fe(H₂O)₆](SO₄)₂·6 H₂O, also known as ferric ammonium sulfate or iron alum, is a double salt in the class of alums, which consists of compounds with the general formula AB(SO₄)₂ · 12 H₂O. It has the appearance of weakly violet, octahedrical crystals.
Formula: NH4Fe(SO4)2