Nomenclature of the triphylite group of minerals

In this paper we present a Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC)-accepted scheme for the classification and nomenclature of the triphylite group of minerals. The general formula of those minerals is M1M2TO 4 , where M1 and M2 refer to cations in an octahedral coordination: M1 = , Na, Li; M2 = Mn 2+ , Fe 2+ , Mg, Fe 3+ , Mn 3+ , and T to tetrahedrally coordinated P 5+ cations. The group contains the Li-bearing phosphates triphylite [LiFe 2+ (PO 4)] and lithiophilite [LiMn 2+ (PO 4)] and their oxidation products heterosite [Fe 3+ (PO 4)] and purpurite [Mn 3+ (PO 4)], as well as the Na-bearing phosphates natrophilite [NaMn 2+ (PO 4)] and karenwebberite [NaFe 2+ (PO 4)]. The Li-Mg-bearing phosphate simferite has been redefined as LiMg(PO 4). Ferrisicklerite and sicklerite correspond to intermediate phases in the triphylite-heterosite and lithiophilite-purpurite solid solutions; consequently, according to the CNMNC dominant-constituent rule, they are discredited. A new mineral oxidation sequence is defined, which considers the different oxidation capacity of iron and manganese, and therefore replaces the traditional Quensel-Mason sequence. The formula calculation procedure for Li-bearing species, based on electron microprobe analyses and single-crystal X-ray diffraction data, is also described.