Synthetic manganosite was converted to manganite by progressive mortar dry grinding (in air). The grinding process which lasted 203 hours was followed by X-ray powder diffraction (XRD), infrared spectroscopy (IR) and surface area determinations. Both the XRD and IR results show that parallel to the gradual structural degradations of manganosite (starting material) and of hausmannite (intermediary phase), the nascent manganite phase undergoes further crystallization, reaching stability in the last stages of grinding. Such a mechanochemical transformation of manganosite into manganite by mortar dry grinding is peculiar, as it was not observed by other grinding methods employed before. Some hypothesis are proposed in order to explain this solid-state transformation.