The octahedral contribution has already been previously observed in slags by other researchers and has been tentatively assigned to Al in melilite ((Ca,Na)2(Al,Mg,Fe)[(Al,Si)SiO7]), which is a solid solution of gehlenite (Ca2Al2SiO7) and akermanite (Ca2MgSi2O7). However, none of these crystalline phases was visible on the diffractogram of the unreacted slag (Figure ). Only a large bump is visible at around 30°,