Nomenclature and Classification of the Arctite Supergroup.Aravaite, Ba2Ca18(SiO4)6[(PO4)3(CO3)]F3O, a New Arctite Supergroup Mineral from Negev Desert, Israel

Abstract

ABSTRACT The crystal structure of arctite, (Na5Ca)Ca6Ba(PO4)6F3 (Rm, a = 7.904 Å, с = 41.320 Å), was refined in 1984 by E. Sokolova. According to modern concepts, this mineral belongs to the intercalated antiperovskites and is characterized by intercalation of triple antiperovskite layers {[F3(Ca7Na5)](PO4)4}4+ and tetrahedral layers Ba(PO4)24–. The pyrometamorphic rocks of the Hatrurim Complex, which are distributed along the Dead Sea Rift, are the origin of eight new minerals with intercalated antiperovskite structures, all discovered within the last five years. Therefore, an update and improvement of the classification and nomenclature was required. The new classification of the arctite supergroup was approved by the CNMNC IMA (Memorandum 95–SM20). The arctite supergroup combines the arctite group (minerals with triple antiperovskite layers), which includes arctite, (Na5Ca)Ca6Ba(PO4)6F3; nabimusaite, KCa12(SiO4)4(SO4)2O2F; dargaite, BaCa12(SiO4)4(SO4)2O3; and ariegilatite, BaCa12(SiO4)4(PO4)2F2O, with the zadovite group (minerals with single antiperovskite layers), which includes zadovite, BaCa6[(SiO4)(PO4)](PO4)2F; aradite, BaCa6[(SiO4)(VO4)](VO4)2F; gazeevite, BaCa6(SiO4)2(SO4)2O; and stracherite, BaCa6(SiO4)2[(PO4)(CO3)]F. Another ungrouped member of the arctite supergroup is aravaite, Ba2Ca18(SiO4)6[(PO4)3(CO3)]F3O – a unique mineral which is formed by the ordered intercalation of super-modules of ariegilatite and stracherite. In addition, a description of aravaite as a new mineral is presented in this paper. The crystal structure has been previously published (Krüger et al. 2018). Furthermore, preliminary data for potentially new minerals of the arctite supergroup, found in rocks of the Hatrurim Complex, are discussed.