a) Clinker, in materials science, is a sinter product of limestone and clay (or other secondary raw materials such as fly ash, sand, or slag) heated in kilns. Clinker is used as the primary component for Portland cement and is typically composed of calcium silicate (CS) phases such as “alite” (Ca₃SiO₅, “C₃S”), “belite” (Ca₂SiO₄, “C₂S”), or “celite” (Ca₃Al₂O₆, “C₃A”).

b) Clinker, in geological sciences, refers to a sedimentary bed that has undergone combustion, such as a coal bed that has undergone combustion and alteration by an igneous intrusion or by a coal-bed fire. Clinker may also refer to a pyroclastic or lava mass that resembles furnace slag.
Cf., calcium silicate phases; fly ash; slag, blast-furnace; kiln, rotary; Portland cement.