The C3S that forms in a cement clinker contains about 3-4% of oxides other than CaO and SiO2. Strictly speaking, this mineral should therefore be called alite rather than C3S. However, as discussed in Section 3.2, we will avoid using mineral names in this monograph. In a typical clinker the C3S would contain about 1 wt% each of MgO, Al2O3, and Fe2O3, along with much smaller amounts of Na2O, K2O, P2O5, and SO3 [2]. These amounts can vary considerably with the composition of the raw materials used to make the cement, however. Of the three major impurities, Mg and Fe replace Ca, while Al replaces Si.