A compound with three forms: monobasic, MgH₄(PO₄)₂_2H₂O, used in medicine and wood fireproofing; dibasic, MgHPO₄_3H₂O, used in medicine and as a plastics stabilizer; tribasic, Mg₃(PO₄)₂_8H₂O, used in dentifrices, as an adsorbent, and in pharmaceuticals.