Unusual Sr-Rich Phosphates of the Apatite Supergroup from the Lovozero Alkaline Massif, Kola Peninsula

Previously unknown trigonal variety of fluorisgaitte (fluorisgaitte-T), a rare Ca-Sr phosphate from the hedyphane group of the apatite supergroup, has been identified in foyatie of the eudialyte complex on Mount Sengischorr of the Lovozero alkaline massif (Kola Peninsula). A low-fluorine analogue of fluorisgaitte has also been revealed in this location (Mt. Sengischorr) within the polkilitic sodalite syenite of the Polkilitic complex. The morphology and mineral associations of studied phosphates indicate their late crystallization within the rocks formed in the end of magmatic stage of the massif formation. Chemical compositions of these two minerals are similar in high contents of sodium and rare-earth elements, being though significantly different in the content of fluorine. The differences in ordered cation distribution within the crystal structures of described minerals lead to the different space group symmetry, i. e., P-3 for the mineral from foyatie, P6₃/m for the mineral from the polkilitic sodalite syenite. We have identified the fluorisgaitte-belovite solid-solutions series. The compositions of studied samples of Sr-rich phosphates (fluorisgaitte-T and low-fluorine analogue of fluorisgaitte) are determined to be near the borderline between the end-members of the series.

Sr-rich phosphate, fluorisgaitte, hedyphane group, apatite supergroup, crystal structure, solid-solution series, alkaline rocks, Lovozero massif, Kola Peninsula