Classification of the minerals of the graftonite group

摘要

A classification and nomenclature scheme has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification for the minerals of the graftonite group. The crystal structures of these minerals have three distinct sites that are occupied by Fe2+, Mn2+ and Ca2+. These sites have coordination numbers [8], [5] and [6], and these differences lead to very strong order of Fe2+, Mn(2+ )and Ca2+ over these sites. As a result of this strong order, the following compositions have been identified as distinct species: graftonite: FeFe2(PO4)(2); graftonite-(Ca): CaFe2(PO4)(2); graftonite-(Mn): MnFe2(PO4 )(2); beusite: MnMn2 (PO4) (2); and beusite-(Ca): CaMn2(PO4)(2).