Abstract: An improved process for producing portland and portland type cement clinker wherein argillaceous and calcareous type materials are ground and blended to form a generally homogeneous mixture and subsequently burned in a kiln at a temperature in the range of about 1200.degree. C. to about 1500.degree. C. to form cement clinker, the improvement comprising incorporating into the mixture a fluorine containing mineral acid, selected from the group comprising fluotitanic acid, fluoboric acid, fluophosphoric acid, fluosilicic acid, and hydrofluoric acid, as a fluxing and mineralizing agent, in an amount of up to 3.0% by weight based upon the weight of the dry solids in the mixture.