This is the first of a three-part series studying the effects of fluxes and mineralizers to increase efficiency of the cement clinkering processes. The effects of flux mineralizers, primarily fluosilicates and fluorides upon phase equilibria in the system CaO-Al₂O₃-Fe₂O₃- SiO₂ (C-A-F-S) and its subsystems C-A-F and C-A-S have been investigated. In both the latter subsystems the temperatures for first liquid formation are lowered substantially, the primary phase field areas of C₁₂A₇ solid solution are vastly expanded, the field areas of C₃A are much diminished, and in the C-A-S system an Alkemade line appears to be formed between C₁₂A₇ solid solution and C₃S, resulting in the stable existence of C₃S over a broader composition range than in the pure C-A-S system. This also results in the formation of new invariant points. Furthermore, reaction to form C₃S is accelerated; its formation takes place at temperatures below the apparent lower stability limit in the pure C-S system; and its primary phase field area is increased in size. Portions of the C-A-F-S system with fluosilicate were studied. When Fe₂O₃ was added to the C-A-S (CaSiF₆) system in amounts from five to twenty percent, C₁₂A₇ solid solution was still found to be the dominant phase. Some of the phase boundaries determined from the C-A-F and C-A-S systems with sluosilicate, logically can be extrapolated into the complex C-A-F-S system + fluosilicate and are experimentally observed. The effects upon phase relations and related kinetic phenomena appear to be favorable to the cement clinker manufacturing process; resulting in greater kiln efficiency.