 Iron ( III ) chloride , also called ferric chloride , is an industrial scale commodity chemical compound , with the formula FeCl3 and with iron in the + 3 oxidation state . The colour of iron ( III ) chloride crystals depends on the viewing angle : by reflected light the crystals appear dark green , but by transmitted light they appear purple @-@ red . Anhydrous iron ( III ) chloride is deliquescent , forming hydrated hydrogen chloride mists in moist air . It is rarely observed in its natural form , mineral molysite , known mainly from some fumaroles . 
