DISSYMMETRYZATION AND POLYMORPHISM IN THE APATITE GROUP MINERALS. R.K. Rastsvetaeva, Inst. of Crystallography RAS, Leninskii pr.59, Moscow, 117333; A.P. Khomyakov, Inst. Miner. Rare Elem., Veresaev str.15 Moscow, 121357

Due to extremely high ability to isomorphism, apatites can be used as natural absorbents of polluting components to solve some ecological problems. That's why studying of apatite group minerals is very actual. New minerals Deloneite-(Ce) NaCa₃Ce(PO₄)₃F and ordered apatite Ca₃R_1.8(PO₄)₃F (R=Sr,Na,Ce) occur in the hyperagpaitic pegmatites of the Khibina alkaline massif (Kola Peninsula). Parameters of both minerals cell: a=9.51(1), c=7.01(1)Å, space group P₃;a=9.485(3),c=7.000(3)Å, space group P₆₃.X-ray single crystal analysis was performed on CAD-4F ENRAF-NONIUS autodiffractometer, 735 and 637 IFI, R=4.9% and 2.9% respectively. Inspite of the fact that deloneite is isotypical to belovite NaSr₃Ce(PO₄)₃F (space group P_-3) these two minerals differ not only in the stoichiometry, but also in their crystal structures and other characteristics. Also new apatite has special peculiarities in comparison with fluoroapatite Ca₅(PO₄)₃F and Srapatite (Sr,Ca)₅(PO₄)₃F. The series of apatite-like minerals A₅(PO₄)₃X (A=Na, Ca,Sr,TR; X=F,Cl,OH): apatite - new R-apatite - belovite - deloneite is characterized by the low- erig of symmetry P₆₃/m - P₆₃ - P_-3 -P₃ due to the cationic and additional anionic ordering in their structures. This fact allowed us to consider the possible reasons of this phenomena and suggest a new nomenclature using 6 end-members for the describeing and compareing chemical distinctions of these complicated phosphates.