Without compositional information, careful measures of intensity of the PXRD peaks, or use of alternative diffraction techniques such as neutron diffraction, there is no way to confirm whether the Ca containing compounds have been made. The same is true for the last of these compounds, MgNi(PO 3 ) 4 -although this is a combination of two metals known to form tetrametaphosphates, there is no way to know from the data presented that the material produced contains both metal ions, or whether they are ordered as predicted. The fit for this particular sample is also much poorer than the others discussed in this paragraph.