Ferro phosphorus is a ferroalloy, an alloy of iron and phosphorus. It contains a high proportion of iron phosphides, Fe2P and Fe3P. Its CAS number is 8049-19-2. The usual grades contain either 18 or 25% of phosphorus. It is a gray solid material with a melting point between 1050-1100 °C. It may liberate phosphine in contact with water. Very fine powder can be combustible.