Magnesium phosphate cements have attracted an increasing attention for biomedical applications in the past years due to their high mechanical performance and fast in vivo degradation at bony implantation sites. Cements are usually multicomponent mixtures of cement raw powders and setting regulators, whereas the latter may have a detrimental effect on the biocompatibility. Here, we demonstrate that following prolonged grinding of trimagnesium phosphate (Mg-3(PO4)(2), farringtonite), a mechanically induced disordering reaction strongly altered farringtonite reactivity such that self-setting cements without further components were formed with a compressive strength of up to 11 MPa. Time-resolved X-ray diffraction analysis revealed that the formation of a nanocrystalline magnesium phosphate phase during grinding was responsible for cement setting to the highly hydrated magnesium phosphate mineral cattiite (Mg-3[(PO4)(2).22H(2)O), whereas crystalline farringtonite showed practically no setting reaction.