Calcium silicate (CS) phases are common to clinker. CS phases are mainly formed by heating calcium carbonate (e.g., limestone for Ca) together with aluminum silicate (e.g., any available clay minerals for Si, Al) phases to temperatures to >1200^oC. In practice, often marls, which are low in cost, are used as they combine carbonates and 2:1 layer phyllosilicates. Typical CS phases are “alite” (Ca₃SiO₅, “C₃S”), “belite” (Ca₂SiO₄, “C₂S”), or “celite” (Ca₃Al₂O₆, “C₃A”). These phases are responsible for the hardening effect of cement as they hydrate under the addition of water forming CSH phases.
Cf., calcium silicate hydrate (CSH) phases, clinker