Calcium aluminoferrite (Ca2(Al,Fe)2O5) is a dark brown crystalline phase commonly found in cements. In the cement industry it is termed tetra-calcium aluminoferrite or ferrite. In cement chemist notation (CCN), it is abbreviated as C4AF meaning 4CaO·Al2O3·Fe2O3 in the oxide notation. It also exists in nature as the rare mineral brownmillerite.