Dimagnesium phosphate is a compound with formula MgHPO<sub>4</sub>. It is a Mg<sup>2+</sup> salt of monohydrogen phosphate. The trihydrate is well known, occurring as the mineral newberyite.
It can be formed by reaction of stoichiometric quantities of magnesium oxide with phosphoric acid.
If monomagnesium phosphate is dissolved in water, it forms phosphoric acid and deposits a solid precipitate of dimagnesium phosphate trihydrate:
The compound is used as a nutritional supplement, especially for infants and athletes. Its E number is E343.