Monazite polymorphism

Bo.M2(P04)3. The thorium, uranium, and neptunium phosphates of general formula Bo 5M2(P04)3 with B = Be, Mg, Ca, Sr, Ba are characterized by extensive polymorphism [5,53,60,61,62,63,64]. As a result of thermal treatment of Mg, Ca, and Sr neptunium phosphates with unknown structures in an Ar + 5% H2 atmosphere, these compounds were established [5,53] as substances crystallizing with the monazite structure type. The authors of [35] have obtained a series of neptunium phosphates with an analogous composition by interaction between solutions of salts of divalent metals (Mg, or Ca, or Sr) with neptunium oxide Np02 and phosphoric acid followed by thermal stage-by-stage treatment... 

BM(P04). The existence of polymorphic modifications is t5q)ical for Th and U phosphates BM(P04)2. Their crystallization led to formation of monoclinic phases with the monazite structure t5q)e. The minerals brabantite (CaTh(P04)2) and huttonite (ThSi04) belong to the monazite structure t5q)e as well. Tetragonal phases have the zircon (ZrSi04) structure t5q)e [10, 53,65-70,71],... 

---