Nomenclature of the apatite supergroup minerals

Abstract

The apatite supergroup includes minerals with a generic chemical formula IXM12 VII M23(IVTO 4)3X (Z1/4 2); chemically they can be phosphates, arsenates, vanadates, silicates, and sulphates. Themaximum space group symmetry is P63/m, but severalmembers of the supergroup have a lower symmetry due to cation ordering and deviations from the ideal topology, which may result in an increase of the number of the independent sites. The apatite supergroup can be formally divided into five groups, based on crystal-chemical arguments: apatite group, hedyphane group, belovite group, britholite group, and ellestadite group. The abundance of distinct ions which may be hosted at the key-sites [M=Ca2+, Pb2+, Ba2+, Sr2+, Mn2+, Na+, Ce3+, La3+, Y 3+, Bi3+; T=P5+, As5+, V 5+, Si4+, S6+, B3+; X = F -, (OH)-, Cl-] result in a large number of compositions which may have the status of distinct mineral species. Naming of apatite supergroup minerals in the past has resulted in nomenclature inconsistencies and problems. Therefore, an ad hoc IMA-CNMNC Subcommittee was established with the aim of rationalizing the nomenclature within the apatite supergroup and making some order among existing and potentially new mineral species. In addition to general recommendations for the handling of chemical (EPMA) data and for the allocation of ions within the various sites, the main recommendations of this subcommittee are the following: 1. Nomenclature changes to existing minerals. The use of adjectival prefixes for anions is to be preferred instead of modified Levinson suffixes; accordingly, six minerals should be renamed as follows: apatite-(CaF) to fluorapatite, apatite-(CaOH) to hydroxylapatite, apatite-(CaCl) to chlorapatite, ellestadite-(F) to fluorellestadite, ellestadite-(OH) to hydroxylellestadite, phosphohedyphane-( F) to fluorphosphohedyphane. For the apatite group species these changes return the names that have been used in thousands of scientific paper, treatises and museum catalogues over the last 150 years. The new mineral IMA 2008-009, approved without a name, is here named stronadelphite. Apatite-(SrOH) is renamed fluorstrophite. Deloneite-(Ce) is renamed deloneite. The new mineral IMA 2009-005 is approved with the name fluorbritholite-(Y). 2. Potentially new mineral species. The following end-member compositions are eligible for status as distinct mineral species; the approved name, if any, is given in parentheses: Ca2Pb3(AsO4)3(OH) (hydroxylhedyphane); Ca2Pb3(PO4) 3(OH) (hydroxylphosphohedyphane). Ca2Sr 3(PO4)3F (new root name); Mn2Ca 3(PO4)3Cl (new root name); Pb 5(SiO4)1.5(SO4)1.5(OH) (hydroxylmattheddleite). 3. Minerals and mineral names which could be discredited. The mineral ellestadite-(Cl) is not thought to exist and should be discredited; the name melanocerite-(Ce) should be discontinued [= tritomite-(Ce)]. 4. Changes of status from distinct species to polymorphic variants. Fermorite is the monoclinic polymorph of johnbaumite (= johnbaumite-M); clinohydroxylapatite is the monoclinic polymorph of hydroxylapatite (= hydroxylapatite-M); clinomimetite is the monoclinic polymorph of mimetite (= mimetite-M). 5. Recognition of a new polymorphic variant. A new monoclinic polymorph of apatite is recognized (chlorapatite-M). 6. Changes to end-member formulae. The ideal chemical formula of morelandite is Ca 2Ba3(AsO4)3Cl instead of Ba 5(AsO4)3Cl; the ideal chemical formula of deloneite is (Na0.5REE0.25Ca0.25) (Ca 0.75REE0.25) Sr1.5 (CaNa0.25REE 0.25) (PO4)3 F0.5(OH)0.5. Show more