When magnesium ammonium phosphate is heated, it is converted to

$$\begin{gathered} \mathrm{Mg}\left({\mathrm{NH}}_4\right){\mathrm{PO}}_4 \stackrel{\mathrm{Strong} \mathrm{Heating}}{\to } {\mathrm{Mg}}_2{\mathrm{P}}_2{\mathrm{O}}_7 \\ \mathrm{Magnesium} \mathrm{pyrophosphate} \end{gathered}$$