Hydroxylhedyphane, Ca2Pb3(AsO4)3(OH), a new member of the apatite supergroup from Långban, Sweden

Fluoralforsite, Ba5(PO4)3F – a new apatite-group mineral from the Hatrurim Basin, Negev Desert, Israel

“…In our study, the chemical analyses and single-crystal X-ray diffraction data indicate the dominance of barium at M2 sites and slight occupancy at the M1 site, enabling the sample investigated to be included in the apatite group. A similar issue has been investigated by Biagioni et al (2019) for hydroxylhedyphane Ca 2 Pb 3 (AsO 4 ) 3 (OH) (P 3), in which the M1 site splits into M1 and M1' but with Ca as the dominant cation at both sites. On that basis the authors classified the mineral as belonging to the hedyphane group and suggested the possible occurrence of intermediate phases between hedyphane and belovite groups (Biagioni et al, 2019).…”

“…A similar issue has been investigated by Biagioni et al (2019) for hydroxylhedyphane Ca 2 Pb 3 (AsO 4 ) 3 (OH) (P 3), in which the M1 site splits into M1 and M1' but with Ca as the dominant cation at both sites. On that basis the authors classified the mineral as belonging to the hedyphane group and suggested the possible occurrence of intermediate phases between hedyphane and belovite groups (Biagioni et al, 2019). Likewise, the data provided here about the new mineral speciesfluoralforsite indicate the possibility of the existence of intermediate phases between belovite and apatite groups and suggest a possible new member of the belovite group with end-member formula BaCaBa 3 (PO 4 ) 3 F and symmetry P6 3 or P 3.…”

“…6b). Assuming the cations are ordering at M1, the symmetry would lower to P6 3 , similar to fluorcaphite and fluorstrophite (belovite group) or even to P 3 such as in kuannersuite-(Ce) and hydroxylhedyphane (Table 1; Friis et al, 2004;Pekov et al, 2010;Biagioni et al, 2019). Monoclinic symmetry is also probable, such as in pure synthetic hydroxyl-and chlorapatite, where anionic column ordering results in a double b unit cell parameter (Hughes and Rakovan, 2002;Pasero et al, 2010).…”

“…5b), whereas in kuannersuite-(Ce) (P 3, belovite group) and hydroxylhedyphane (P 3, hedyphane group) a displacement off the polyhedra edge parallel to c was observed. We consider that the tilting is related to anions or M1-cations ordering (Friis et al, 2004;Biagioni et al, 2019). In fluoralforsite, the O2 sites are shifted from the unique position (.m) in order to obtain a favourable bond distance with the large Ba cation and the smaller Ca cation.…”