Calcium Selenophosphate

Two selenophosphates, CaHPSeO₃. 2CaHPO₄.15H₂O and CaHPSeO₃.8H₂O, in which part of the oxygen is replaced by selenium, have been described.

Various double phosphates of the alkalies with calcium are known: the orthophosphates, CaKPO₄, CaNaPO₄ and Ca₃Na₆(PO₄)₄, Ca(NH₄)PO₄.7H₂O; the pyrophosphates, CaK₂P₂O₇ and CaNa₂P₂O₇.4H₂O; and the metaphosphates, 2Ca(PO₃)₂.2NaPO₃. 6H₂O and Ca(PO₃)₂.2NH₄PO₃.2H₂O.

A uranium calcium phosphate, UO₂.CaO.P₂O₅, and a thorium calcium phosphate, ThO₂.CaO.P₂O₅, have been isolated, and there is a natural calcium manganese phosphate, fairfieldite, (Ca,Mn)₃(PO₄)₂, and also a natural calcium uranyl phosphate, autunite, Ca(UO₂)₂(PO₄)₂.8H₂O.