The XRD patterns of the powders obtained after milling are shown in Fig. . The milling process between KH2PO4 and eggshell (98% of CaCO3) performed from 2 h and 400 rpm produce a mixture of phosphates, mainly K3CaH(PO4)2 (PDF database n° 22-1218 indicated by black columns, and black dash lines guiding the comparison with the samples) and possibly CaKPO4 (PDF database n° 33-1002 indicated by red columns, and red dash lines guiding the comparison with the samples). Bellow these milling parameters (time and milling speed) only the reactants diffraction patterns are found, i.e., no evidence of chemical reaction is observed. There is a direct relationship between the time and milling speed and the increasing of total energy involved. In general, it was noticed that only a minimal energy is required to initiate the mechanochemical reaction and, as a consequence, the diffraction patterns have huge changes attributed to the formation of different polymorphic potassium calcium phosphate phases. When milling time increases, secondary reactions begin, for example, mechanochemical dehydroxylation of the new formed phosphates. One can propose the non-stoichiometric reaction of the main products, with CaKPO4 more evident after 24 h of milling: