A green-yellow deliquescent compound, FeCl2; hexagonal; r.d. 3.16; m.p. 670°C. It also exists in hydrated forms: FeCl2.2H2O (green monoclinic; r.d. 2.36) and FeCl2.4H2O (blue-green monoclinic deliquescent; r.d. 1.93). Anhydrous iron(II) chloride can be made by passing a stream of dry hydrogen chloride over the heated metal; the hydrated forms can be made using dilute hydrochloric acid or by recrystallizing with water. It is converted into iron(III) chloride by the action of chlorine.