the pyrochlore supergroup of minerals: nomenclature

673

The Canadian MineralogistVol.48,pp.673-698(2010)DOI:10.3749/canmin.48.3.673

THE PYROCHLORE SUPERGROUP OF MINERALS: NOMENCLATURE

DanielaTenCiO§

Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, 05508-080, São Paulo, SP, Brazil

MarCelOB.anDraDe

Instituto de Física de São Carlos, Universidade de São Paulo, 13560–970, São Carlos, SP, Brazil

anDrewG.CHriSTY

Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

reTOGierÉ

Institut für Geowissenschaften, Albert-Ludwigs-Universität, Albertstrasse 23b, D–79104 Freiburg, Germany

PavelM.KarTaSHOv

Institute of Geology, Ore Deposits, Petrography, Mineralogy and Geochemistry (IGEM), Russian Academy of Sciences, Staromonetnyi pereulok 35, 109017, Moscow, Russia

aBSTraCT

Anewschemeofnomenclature for thepyrochlore supergroup, approvedby theCNMNC–IMA, isbasedon the ionsattheA,B andY sites.What has been referred to until nowas the pyrochlore group shouldbe referred to as the pyrochloresupergroup,andthesubgroupsshouldbechangedtogroups.Fivegroupsarerecommended,basedontheatomicproportionsoftheBatomsNb,Ta,Sb,Ti,andW.Therecommendedgroupsarepyrochlore,microlite,roméite,betafite,andelsmoreite,respectively.Thenewnamesarecomposedoftwoprefixesandonerootname(identicaltothenameofthegroup).Thefirstprefixreferstothedominantanion(orcation)ofthedominantvalence[orH2Oor□]attheYsite.Thesecondprefixreferstothedominantcationofthedominantvalence[orH2Oor□]attheAsite.Theprefix“keno-”represents“vacancy”.Wherethefirstandsecondprefixesareequal,thenonlyoneprefixisapplied.Completedescriptionsaremissingforthemajorityofthe pyrochlore-supergroup species.Only sevennames refer to valid species on the grounds of their complete descriptions:oxycalciopyrochlore, hydropyrochlore, hydroxykenomicrolite, oxystannomicrolite, oxystibiomicrolite, hydroxycalcioroméite,and hydrokenoelsmoreite. Fluornatromicrolite is an IMA-approvedmineral, but the complete description has not yet beenpublished.The following20names refer tominerals thatneed tobecompletelydescribed inorder tobeapprovedasvalidspecies: hydroxycalciopyrochlore, fluornatropyrochlore, fluorcalciopyrochlore, fluorstrontiopyrochlore, fluorkenopyrochlore,oxynatropyrochlore, oxyplumbopyrochlore, oxyyttropyrochlore-(Y), kenoplumbopyrochlore, fluorcalciomicrolite,oxycalciomicrolite, kenoplumbomicrolite, hydromicrolite, hydrokenomicrolite, oxycalciobetafite, oxyuranobetafite,fluornatroroméite,fluorcalcioroméite,oxycalcioroméite,andoxyplumboroméite.Forthese,thereareonlychemicalorcrystal-structuredata.Typespecimensneedtobedefined.Potentialcandidatesforseveralotherspeciesexist,butarenotsufficientlywellcharacterizedtograntthemanyofficialstatus.Ancientchemicaldatarefertowet-chemicalanalysesandcommonlyrepresentamixtureofminerals.Thesedatawerenotusedhere.Alldatausedrepresentresultsofelectron-microprobeanalysesorwereobtainedbycrystal-structurerefinement.Wealsoverifiedthescarcityofcrystal-chemicaldataintheliterature.Therearecrystal-structure determinations published for only nine pyrochlore-supergroupminerals: hydropyrochlore, hydroxykenomicrolite,hydroxycalcioroméite, hydrokenoelsmoreite, hydroxycalciopyrochlore, fluorcalciopyrochlore, kenoplumbomicrolite,oxycalciobetafite, andfluornatroroméite.The followingmineral names are nowdiscarded: alumotungstite, bariomicrolite,bariopyrochlore, bindheimite, bismutomicrolite, bismutopyrochlore, bismutostibiconite, calciobetafite, ceriopyrochlore-(Ce),cesstibtantite, ferritungstite, jixianite, kalipyrochlore,monimolite, natrobistantite, partzite, plumbobetafite, plumbomicrolite,

§ E-mail address:[email protected]

674 THeCanaDianMineralOGiST

plumbopyrochlore, stannomicrolite, stetefeldtite, stibiconite, stibiobetafite, stibiomicrolite, strontiopyrochlore, uranmicrolite,uranpyrochlore,yttrobetafite-(Y),andyttropyrochlore-(Y).

Keywords:pyrochloresupergroup,nomenclature,pyrochloregroup,microlitegroup,betafitegroup,roméitegroup,elsmoreitegroup.

SOMMaire

Nousproposonsunnouveausystèmedenomenclaturepourlesminérauxdusupergroupedupyrochlore,sanctionnéparleComitédesNomsdeMinéraux,deNomenclatureetdeClassificationdel’AssociationinternationaledeMinéralogie,etfondésurlesionssetrouvantauxsitesA,BetY.Cequiadéjàétéconsidérélegroupedupyrochloredevientlesupergroupedupyrochlore,etlessous-groupesdeviennentdorénavantdesgroupes.Cinqgroupessontmaintenantrecommandés,selonlaproportiondesatomesNb,Ta,Sb,Ti, etWau siteB.Les groupes recommandés sont nomméspyrochlore,microlite, roméite, bétafite, etelsmoreïte,respectivement.Lesnouveauxnomscontiennentjusqu’àdeuxpréfixesetunnom-racine,quiestidentiqueaunomdugroupe.Lepremierpréfixefaitallusionàl’anionprédominant(oucation)delavalencedominante[ouH2Oou□]ausiteY.Lesecondserapporteaucationprédominantdelavalencedominante[ouH2Oou□]ausiteA.Lepréfix“kéno-”représente“lacune”.Danslescasoùlepremieretlesecondpréfixesontlesmêmes,seulunpréfixesuffira.Desdescriptionscomplètesnesontpasdisponiblespourlamajoritédesespècesdusupergroupedupyrochlore.Seulsseptnomsfontréférenceàdesespècesconsidérées valides à cause de leur description complète: oxycalciopyrochlore, hydropyrochlore, hydroxykénomicrolite,oxystannomicrolite,oxystibiomicrolite,hydroxycalcioroméite,ethydrokénoelsmoreïte.Lafluornatromicroliteestuneespèceapprouvée,maisladescriptioncomplètedecetteespècen’apasencoreétépubliée.Lesvingtnomssuivantsserapportentàdesespècesdontladescriptiondoitêtrecomplétéepourêtreconsidéréesvalides:hydroxycalciopyrochlore,fluornatropyrochlore,fluorcalciopyrochlore, fluorstrontiopyrochlore, fluorkénopyrochlore, oxynatropyrochlore, oxyplumbopyrochlore,oxyyttropyrochlore-(Y),kénoplumbopyrochlore,fluorcalciomicrolite,oxycalciomicrolite,kénoplumbomicrolite,hydromicrolite,hydrokénomicrolite, oxycalciobetafite, oxyuranobétafite, fluornatroroméite, fluorcalcioroméite, oxycalcioroméite, etoxyplumboroméite.Danscescas,iln’yaquedesdonnéeschimiquesoudesdonnéessurlastructurecristalline.Ondoitdéfinirdes échantillons-types.Dans plusieurs autres cas, des candidats potentiels existent,mais ils ne sont pas suffisamment biencaractériséspourleurattribuerunstatutofficiel.Lesdonnéeschimiquesplusanciennesreposentsurdesanalysesparvoiehumide,etreprésenteraientengénéraldesmélanges.Detellesdonnéesn’ontpasétéutiliséesici.Touteslesdonnéesreprésententdoncdesrésultatsd’analysesobtenuesavecunemicrosondeélectroniqueoubiendesdonnéesétabliesparanalysedelastructurecristalline.Nousavonsaussivérifiélararetédesdonnéescristallochimiquesdanslalittérature.Nousavonstrouvédesdéterminationsdelastructurecristallinepourseulementneufminérauxdusupergroupedupyrochlore:hydropyrochlore,hydroxykénomicrolite,hydroxycalcioroméite, hydrokénoelsmoreïte, hydroxycalciopyrochlore, fluorcalciopyrochlore, kénoplumbomicrolite,oxycalciobetafite,etfluornatroroméite.Lesnomssuivantsdeviennentdésuets:alumotungstite,bariomicrolite,bariopyrochlore,bindheimite, bismutomicrolite, bismutopyrochlore, bismutostibiconite, calciobétafite, cériopyrochlore-(Ce), cesstibtantite,ferritungstite,jixianite,kalipyrochlore,monimolite,natrobistantite,partzite,plumbobétafite,plumbomicrolite,plumbopyrochlore,stannomicrolite, stetefeldtite, stibiconite, stibiobétafite, stibiomicrolite, strontiopyrochlore, uranmicrolite, uranpyrochlore,yttrobétafite-(Y),etyttropyrochlore-(Y).

(TraduitparlaRédaction)

Mots-clés:supergroupedupyrochlore,nomenclature,groupedupyrochlore,groupedumicrolite,groupedelabétafite,groupedelaroméite,groupedel’elsmoreïte.

Theofficialpyrochlore-supergroupsystemofclas-sification (Hogarth1977)doesnot follow the currentIMA rules ofmineralogical nomenclature, althoughthat system is currently still approved by IMA.Hogarth (1977) assigned species prefixes accordingto the chemical composition of theA position of thepyrochloreformula.Speciesinwhichanexoticcation(i.e.,anythingotherthanCaorNa)madeupmorethan20%of the total number ofA cationswere assigneda special prefix indicating thepresenceof the cation.Insuchcases,theprefixwastoapplytothedominantexoticcation.Forexample,amemberofthepyrochloregroupwith 25% Pb and 20% Srwould be namedplumbopyrochlore,with “strontian”, as an optional(varietal)adjectivalmodifier.At theA site,Hogarth’s(1977)systemdoesnotdifferentiatebetweenoccupancy

inTrODuCTiOn

In 1977, Hogarth presented a comprehensiveclassification and nomenclature for the pyrochloresupergroup,which represented the then-current bodyofknowledgeonpyrochlore-supergroupminerals.Thestudyproducedaconciseclassification,andreducedtheproliferationofsynonymstoahandfulofnames.TheIMACNMMN(nowCNMNC)has recently receiveda series of submissions for potentially newmembersof the pyrochlore supergroup. Some of the submis-sionsinvokednewinterpretationsorextensionsoftheapproachofHogarth(1977).Inaddition,someCommis-sionmembers expressed concern about Hogarth’sspeciesandgroupdivisions,whichdonotconformtocurrentIMAcriteria(Nickel1992).

THePYrOCHlOreSuPerGrOuPOfMineralS:nOMenClaTure 675

byCaandNa.Inspiteofthis,thespeciesfluornatro-microlitewasapprovedon thebasisofpredominanceofNaattheAsite.The natro-prefixisalsopresentinthenamenatrobistantite.Theprefixcalcio-wasusedfor calciobetafite (Mazzi&Munno1983).RegardingtheB-site occupancy, the division among the groupsisnotmadewithatripartitesymmetricalclassification(assuggestedbyZurevinski&Mitchell2004),norisitbasedonthedominant-valencerule(asadoptedinthisproposal).ThespecieswithNb+Ta>2TiandNb>Taareconsideredaspyrochlore-groupminerals;ifNb+Ta>2TiandTa≥Nb,themineral isconsideredtobelong to themicrolite group, and if 2Ti≥Nb+Ta,themineralbelongstothebetafitegroup.IsostructuralspecieswithotherpredominantcationsattheBsitewerenotincludedinthepyrochloresupergroup(forexample,roméite,withdominantSb,andelsmoreite,withdomi-nantW).Theanionsarenottakenintoaccountintheclassification, but the predominance of fluorinewasusedfortheapprovalofthespeciesfluornatromicrolite.OthernamesthatdisagreewithIMArecommendations,such as cesstibtantite and natrobistantite,were alsointroducedwithIMAapproval.

Many problematic features of pyrochlore-super-groupminerals and synthetic pyrochlores have beenresolved sinceHogarth (1977).The structural role ofH2O,verylargecations(K,Cs,Rb),atypicalBcations(Fe3+,Zr,W), andcationswith stereoactive lone-pairelectrons(Sb3+,Sn2+)arenowunderstood.Inaddition,modernelectron-probemicroanalysis(EPMA)permitsroutinedeterminationofF,providingbetter-qualitydataontheanioncontent.

A new CNMMN subcommittee on pyrochlore(Chairman: Scott Ercit.Members: PetrČerný,GregLumpkin, ErnieNickel,MilanNovák, andRolandRouse)wasestablishedin1998.Oneinterimreportwasissuedin1999,butnoadditionalreportwaspresentedformallytotheCommissionsincethen.Thissubcom-mitteewasterminatedinJune2008.Anunofficialreportpreparedin2003byScottErcitwasprovidedtothenewsubcommitteeandservedasabasisforthepreparationofthisreport.

The following represents a modernization ofHogarth’s(1977)system,inwhichwehavetakenintoaccounttheideaspresentedinthepaperbyHatert&Burke(2008).Webelievethatthenewnamesbeingproposedaremore rational, and their use should be preferred.

In order tomake this report consistentwith therecently approved definitions of group nomenclaturebyMillset al. (2009),what is up to now referred toas the pyrochlore group should be referred to as thepyrochlore supergroup, and the subgroups should bechangedtogroups.

THefOrMula

Thepyrochlore-supergroupminerals crystallize intheisometriccrystalsystem(spacegroupFd3moritssubgroups)andexhibitaunitcellcharacterizedbya�10.4ÅandZ=8(Rouseet al.1998).Theyconformtothegeneralformula:

A2–mB2X6–wY1–n.

fiG.1. Idealpyrochlorecrystalstructureviewedalongthe[110]axis(Ared,YorangeandBO6octahedraingreen)(Hendersonet al.2007).


In this formula,A typically isa large [8]-coordinatedcationwitharadiusof~1.0Åoravacancy(□),butcanalsobeH2O(includes ionswithorwithout lone-pairelectronsonsites16dor96ginFd3m).TheAsitethereforemayhostNa, Ca, Ag,Mn,Sr, Ba, Fe2+, Pb2+, Sn2+, Sb3+, Bi3+, Y,Ce (andotherREE), Sc,U,Th,□, or H2O.Themainconstituentsareshowninbold.

B is a [6]-coordinated cation (site 16c), typicallyof highfield-strength.This site thusmay containTa, Nb, Ti, Sb5+, W,butalsoV5+,Sn4+,Zr,Hf,Fe3+,Mg,AlandSi.

X typically isO, but can include subordinateOHandF(site48f).

Y typicallyisananion,butcanalsobeavacancy,H2O, or a very large (>> 1.0Å)monovalent cation(site 8b).Examples areOH–, F, O,□,H2O,K,Cs,Rb.Displacementsto96g,32e and 192ipositionswerealsolocated.

Thesymbolsm, w, and nrepresentparametersthatindicateincompleteoccupancyoftheA,XandYsites,respectively.VacancieshavenotbeenfoundtooccurattheBsite(Borodin&Nazarenko1957,vanWambeke1970). Compositionswith a substantial concentra-tionofvacanciesattheAsitehavebeendescribedas“defect pyrochlores”.However, it is undesirable togivethistermofficialstatusinthiscontext,sinceitisnon-specific, and likely to be used to describe otherdeviations from the ideal structureandstoichiometry.Lumpkin&Ewing (1992, 1995), Ercit&Robinson(1994),Bruggeret al.(1997),andNasraoui&Waeren-borgh (2001) noted vacancies at theX site in someextreme cases of secondary alteration.According toLumpkin&Ewing (1995), the following ranges areencountered:m=0to1.7,w=0to0.7,andn=0to1.Actually,m canrangeupto2(Ercitet al.1994,Bruggeret al.1997).

Hogarth et al. (2000), among others, discussedthe distribution of cations at the structural sites ofpyrochlore-supergroupminerals.Syntheticpyrochloreshaveamuchmorevariablechemicalcompositionthannaturalexamples(Subramanianet al.1983).

For structural reasons,A can be subdivided intoconstituentswithoutlone-pairelectrons(e.g.,Na,Ca),whichoccupy16d,andstereoactivecations(e.g.,Sb3+),which occupy less symmetrical positions displacedslightly from16d, e.g., 96g. For the purpose of thisnomenclature,no subdivision ismade.This approachhas its analogues in the nomenclature of silicateminerals. For instance, theA site of the amphiboleformula represents general or special positions, andtheC“site”consistsofthecombinationofthecrystal-chemicallysimilarMltoM3sites.

The pyrochlore structure (Fig. 1) is an essentialbuildingblockforothermineralsandmineralgroups,suchasalunite(Goreaud&Raveau1980)orpittongite(Greyet al.2006).

THenewSCHeMeOfnOMenClaTure

Inthepresentwork,anewschemeofnomenclaturebasedontheionsattheA,BandY sitesispresented.Thenewnamesarecomposedoftwoprefixesandoneroot name (identical to the nameof the group). Fivegroups are recommended, on the basis of the atomicproportions of theB-site atomsNb,Ta, Sb,Ti, andW.Therecommendedgroupsarepyrochlore, micro-lite, roméite, betafite, and elsmoreite, respectively.According to this new scheme, thepyrochlore super-groupnowalsoincludesmineralspecieswithWorSb5+asthedominantcationattheB site.Thesespecieswereonceregardedastungstatesorantimonatesratherthanconventionaloxides,but theycontainW6+orSb5+ inoctahedralcoordinationwithoxygen,andtheresultingoctahedraarepolymerizedtoformtheframeworkofthepyrochlorestructure.Furthermore,theWandSbspeciesshowvariousdegreesofsolidsolutionwith“conven-tional”membersof thesupergroup(Brugger&Gieré1999).ThedeterminationofapropergroupismadebythedominantvalenceatB,notbya single,dominantion.Thatis,thenumbersofalltetravalentcationsaresummedtogiveatotalnumberofM4+,thenumbersofallpentavalentcationstogiveasumM5+,andsoon.Forthispurpose,agroupofatomswiththesamevalencestateareconsidered tobeasingleconstituent (Hatert&Burke2008).

IfM4+>M5+andM4+>M6+,thenthegroupis:Betafite,ifTiisthedominantM4+cation.IfM5+>M4+andM5+>M6+,thenthegroupis:Pyrochlore,ifNbisthedominantM5+cation,Microlite,ifTaisthedominantM5+cation,Roméite,ifSbisthedominantM5+cation.IfM6+>M4+andM6+>M5+,thenthegroupis:Elsmoreite,ifWisthedominantM6+cation.

New root nameswere required for the newW- andSb5+-dominantpyrochloregroups.InaccordancewithHogarth (1977), roméitewill be the root name forspeciesoftheSb5+-dominantpyrochloregroupbecausethis is the name of the Ca–Na-dominant species.However, asnoCa–NamemberhasbeenestablishedfortheW-dominantpyrochloregroup,wehadtochoosearootnameamongthefourspeciesthatwereconsid-ered valid: ferritungstite, alumotungstite, elsmoreite,and jixianite.The three first names are defined anddistinguishedonthebasisofminorconstituentsattheAandB sites(cf.Ercit&Robinson1994,Williamset al.2005).Inallthree,vacanciesaredominantatA,andWisthedominantspeciesofthedominantvalenceatB,sobythecriteriaproposedhere,thesenamesrefertothesamespecies.Ferritungstitewouldhavehistoricalprecedence, as itwas described in 1911bySchaller.


Jixianite,describedin1979byLiuJianchang,referstothemineralwithPbdominantatAandWatB.However,thereisaproblemwith“ferritungstite”astherootnameforaspeciesoftheW-dominantpyrochloregroup:thenameerroneouslyimpliesdistinctcrystallographicrolesforWandFe3+inthestructureofferritungstite.Infact,Fe3+ismerelyasubordinatecationattheW-dominantB siteoftheferritungstitestructure(Ercit&Robinson1994), as isAl in the alumotungstite structure (≡ ferritungstitewith subordinateAl:Ercit&Robinson1994).Thenamecouldbejixianite,butinabsenceofacrystal-structurestudy,itisnotpossibletoknowthedominantanionof thedominantvalenceat theY siteofthismineral.Consequently,thenameforthisgroup,andtherootnameforallspeciesofthisgroup,willbeelsmoreite.Asamineralgroupconsistsoftwoormoreminerals(Millset al.2009),elsmoreitecannotreallybeconsidered,fornow,asamineralgroup.Hydrokenoels-moreiteshouldbedesignatedasanunassignedmemberofthepyrochloresupergroup,becausethereisnoothermembertoallowagrouptobeestablished.

Extensivesolid-solutionexistsamongNb-,Ta-,andTi-dominant pyrochlores.Hogarth (1977) delimitedthe betafite group from theNb andTa groups at the33%markinordertoplacemorecompositionsinthesparsely populatedfield of betafite.Wepropose herethat all group divisions be rearranged in accordancewiththedominantvalenceatB,notbyasingle,domi-nant ion (seeFig.2).Figures2 and3wereextractedfroma preliminaryversionof this proposalmadebythepreviouscommittee.Certainly,theyincluderesultsof bothmicroprobe andwet-chemical analyses.Thetwopoints near theTi corner belong to betafite- androméite-groupminerals.Their apparent position inthe far apex of the triangle is a projection artefactdue to the absence of a Sb5+ corner in the diagram:Ti andSb in nearly equal proportions are the domi-nantB-site cations in theseminerals,withNb andTa almost completely absent. For example, one ofthe oxycalciobetafite compositions is (Ca0.872Ce0.609Mn0.415Na0.051□0.053)S2.000(Ti1.126Sb0.783Nb0.037W0.033Fe0.013V0.008)S2.000O6(O0.634F0.068□0.053) (Brugger&Gieré1999).Pyrochlore-typephaseswithca. 2Tiarewellknownsynthetically[e.g.,CaUTi2O7(Dicksonet al. 1989),Y2Ti2O7 (Matteucci et al. 2007)], but theclusteringofnaturalcompositionsnear (Nb,Sb):Ti=1:1suggestsentropystabilizationatthemiddleofthesolid-solutionseries.RelativelackofTi–Tasolidsolu-tionisanimportantandinterestingdifferencebetweenTaandNb.

The new scheme of nomenclature based on twoprefixes and a root name allows one to use the rootnames without prefixes, or with only one prefix[e.g.,“plumboelsmoreite”] to specify at least a groupformineralsthathavenotbeenfullyanalyzed.Thefirstprefixwill refer to the dominant anion (or cation) ofthedominantvalence[orH2Oor□]attheY site.Thesecondprefixwill refer to thedominantcationof the

dominantvalence[orH2Oor□]at theA site.GiventheClassicalGreekderivationof“oxy-”,“hydro-”and“hydroxy-”,wesuggest“keno-”torepresent“vacancy”,from theGreekkno,meaning “empty”.The termkeno- has been previously suggested by Permingeat(invanWambeke1971)asaprefixmodifierforcation-deficientmembersofthepyrochloresupergroup.Wherethefirst andsecondprefixesareequal, thenonlyoneprefixisapplied(“hydropyrochlore”,not“hydrohydro-pyrochlore”).Theonlyproblemisthatwemightwanttouse“hydropyrochlore”tomeananypyrochloreinthegroupofspecieswithH2OattheYsitesandunspecifiedA-siteoccupancies.

Hogarth (1977) assigned species names incorpo-rating prefixes thatwere determined by theA-sitecompositionofthepyrochloreformula.Theseprefixeswere used to define names of new specieswhere acation other thanCaorNamadeupmore than20%of the total number ofA-site cations. The prefixspecifiedthedominantcationthatisnotNaorCa.Forexample,amemberofthepyrochloregroupwith25%Pbwouldbenamedplumbopyrochlore.Thisapproachhasbeenmodifiedinthenewsystemofnomenclatureto reflect current knowledge of the crystal chemistryof pyrochlore-supergroupminerals, and also to bringpyrochlore nomenclature into better consistencywithcurrentbestpracticeforcomplexsolid-solutions(Hatert&Burke2008).Like theB sites, theA sitesofpyro-chlorescancontainspeciesofseveraldifferentcharges.Theycanalsocontainaneutralmolecularspecies,H2O,andvacancies.ConsistentwiththeprocedurefortheB site,itispossibletogroupA-sitespeciesintovalencegroupsM1+,M2+ and soon, and a zero-chargegroupforH2O and vacant sites.The second prefix is thendeterminedby thedominantspeciesof thedominant-valencegroup,asfollows.

The zero-charge group

The occupancy of theA position in pyrochlore-supergroupmineralsbycations is insomecasesverylow(<50%).Wherethezero-chargegroupexceedsanyvalencegroupoftheAsite,thesecondprefix“keno”isproposedforspeciesinwhich□exceedsH2O,andthesecondprefix“hydro”isproposedforspeciesinwhichH2Oexceeds□.

The dominant valence rule

TheHogarth (1977) rules of nomenclature thatreflectthechemicalcompositionattheApositionhavebeenmodified to conform to thedominant-valence rule.Consequently,whereneutral speciesarenot thelargestvalence-basedgroupattheA position,asecondprefixisnowtobeappliedforthedominantcationofthedominantvalence.ThereisanaturalclusteringofcompositionsnearNa=Ca=1apfu(Fig.3),acharge-balancingrequirementformembersoftheB5+groups.


fiG.2. Pyrochlore-supergroupminerals,B-sitecomposition.

aa

b


Hence,inHogarth(1977),ifthedominantcationwaseitherCa orNa, no prefixwas used, and dominanceof either of these cationswas not indicated. Prefixeswereonlyusedtoindicatesubstantialamountsofothercations. Inorder to regain consistency, it is proposedhere to use secondprefixes fromnowon in order toindicateCaandNapredominance.

The pyrochlore supergroup presents complexitiesin the specification of end-member formulae, andalsowhether single-species names should correspondto single chemical end-members. For some species,a single unambiguous charge-balanced end-memberformula cannot exist. For example, the fluornatro-microlite ofWitzkeet al. (IMA#98–018) existswithcomposition(Na1.15Ca0.70Bi0.15)S2Ta2O6F.Useofonlydominantspeciesateachsitesuggeststheideal“end-member”formulaNa2Ta2O6F,whichisnotelectrostati-callyneutralandhenceisphysicallyimpossible.Intherealmineral,theheterovalentsubstitution2Ca2+=Bi3++Na+ takes place, so it is intermediate between thetwo charge-balanced end-membersNaCaTa2O6F andNa1.5Bi0.5Ta2O6F.Thesecompositionshavecomponentsofmorethanonevalenceononlyonesite,andthusareend-members in the senseofHawthorne (2002).Theboundarybetween these two endmembers is locatedat 50mol.%, and corresponds to the compositionNa1.25Ca0.5Bi0.25Ta2O6F.Theexampleaboveisclosetothisboundary,buthasNaCaTa2O6Fpredominant.Giventhestrongclusteringofpyrochlorecompositionsnearthisendmember,itistemptingtofindawaytodefine

thisendmemberascorrespondingtoonespeciesdespitethe50:50mixedoccupancyoftheAsites,inwhichcasefluornatromicrolitewouldbeaBi-richexampleofthisspecies.We agree that it is unfortunate that a singlecompositionfield,withnomajorchangeinpropertiesorparagenesisandwithcompositionsclusteringaroundthe 50:50mark, should be broken intoNa-dominantandCa-dominant halves.However, the division ofthe composition field does not really present a newnomenclaturaldifficulty.AstheA-siteandY-sitecontentof pyrochlore cannot be establishedwithout analysis,secondprefixescanonlybeusedwithconfidence foranalyzed specimens.Compositions that are near the50:50 composition canbe explicitlyflagged as being“near the 50:50mark”.Root nameswithout prefixesarerecommendedforincompletelyanalyzedmaterial.

Rigorousadherencetotheprincipleofusingasingledominantspeciesinadominant-valencegroupproducesamismatchbetweenspeciesandendmembersinpyro-chlores.Thecharge-balancedend-memberNaCaTa2O6Fisnotatthecenterofthecompositionfieldofaspecies,butmarks the boundary between fluornatromicro-lite and fluorcalciomicrolite. Conversely, neither ofthese species names canbe associatedwith a uniquecharge-balancedend-member.Theformula(Na1.5Bi0.5)Ta2O6Fisanexampleofonepossibleend-memberforfluornatromicrolite,with neutralitymaintainedby thesubordinateBi3+ at theA site.Theminor substituentneednot beBi: (Na1.5Y0.5)Ta2O6F and (Na1.667U0.333)Ta2O6Fareexamplesofendmembersthatwouldshare

fiG.3. Pyrochlore-supergroupminerals,A-sitecomposition.


the same name in our scheme. In order tomaintainsimplicity and avoidproliferationof names, only thepredominantNa is used to determine species, andwe have a “one-to-many”mapping between namesand some endmembers. These endmembers cancollectively be represented as (Na,#)2Ta2O6F,where“#”isunderstoodtomeanasubordinateamountofanunspecifiedcharge-balancingcomponent.Thesituationisanalogousforfluorcalciomicrolite,althoughthe“#”componentsforthatspecieswouldhaveachargelessthan+1 rather than in excess of +2. In this scheme,the “fluornatromicrolite” composition above clearlypertainstofluornatromicrolite,withCaandBiasminorcharge-balancingcomponents.Mismatchofspeciesandendmembersarisesbecause themultiplicityof theAsite(Na,Ca,etc.)istwicethemultiplicityofthenon-frameworkanion site (F,OH,O,H2O), and themostcommonB-site andY-site components require 50:50occupancyofAbytwodifferentvalences.Thisproblemarisesinmanycomplexsolid-solutions,andoursolu-tionforthepyrochloresmayprovideatemplateforthenomenclatureofothermineralgroups.

Nomenclaturebasedonthedominantelementinadominant-valence group is simple and reproducible.Thisisnot truefor thealternativeschemeofoneendmemberisequaltoonename,whichisanotherreasonfor rejecting thatmodel. Inmultidimensionalcoupledsolutions,particularlywherethereareseveraldifferentvalence-groupsatmorethanonesite,itisnoteasytodefine a rigorous, reproducibleway of extracting aunique dominant end-member.An example is shownbelow.

Consideraformulasuchas(Na1.1Ca0.4Y0.2U0.2□0.1)(Nb1.7Ti0.3)O6(OH).Ourrulesquicklyleadtothename“hydroxynatropyrochlore”.However, it is possible topartitionthevariouscationssoastofindagreatmanyend-memberswithinit,forexample:

0.08(□1.25U0.75)Nb2O6(OH)+0.14(NaU)Ti2O6(OH)+0.02Ca2(NbTi)O6(OH)+0.40(Na1.5Y0.5)Nb2O6(OH)+0.36(NaCa)Nb2O6(OH)

but this isnotauniquedecompositionof theformulainto “Hawthornian” end-members. The followingdecomposition also corresponds to the same overallformula:

0.10(□Y)Nb2O6(OH)+0.60(Na1.67U0.33)Nb2O6(OH)+0.10(CaY)Ti2O6(OH)+0.10Ca2(NbTi)O6(OH)+0.10(NaCa)Nb2O6(OH)

inwhich only two out of five end-members are thesame, but their proportions are quite different!Even

identifyingthesingledominantend-memberunambigu-ously is not possiblewithout careful definition of anelaborate procedure.The simplicity and reliability ofourcurrentschememakeitpreferable.

Variability at the Y site

Pyrochlore-supergroupminerals show a variableY-site composition. In the past, variations inY-siteoccupancywerenotreflectedinspeciesnomenclature,inpartowingtoalackofknowledgeofthestructuralchemistryofpyrochlore,butalsoowingtodifficultieswiththedeterminationofsome Yspecies.Asthedomi-nantconstituentat theY positioncannowcommonlybe establishedviaEPMAand structure analysis, it isreasonable to indicate the composition of this site inthe nomenclature.Rouse et al. (1998) demonstratedthe presence of structural (OH) groups by infraredspectroscopy.Thedominant-valencerule isalsovalidforanionicsites(Hatert&Burke2008).Hence,asetofprefixesistobeusedtoindicatethedominantspeciesofthedominant-valencegroupattheYsite.AccordingtoLumpkinet al.(1986),amajordifficultyisthedeter-mination ofwhether the “water” is present asOHormolecularH2O.Borodin&Nazarenko(1957)assumedatotalofsevenanionsandcalculatedtheamountofOHnecessary to achieve charge balance.Excess “water”wasallocatedasH2O. Ingeneral, thisprocedurewillnotalwaysbevalidbecauseofanionvacanciesattheYsite(Pyatenko1959,Aleshin&Roy1962,Subramanianet al.1983,Chakoumakos1984).AssumptionsinvolvedincalculatingstructuralformulaemainlyaffectO,OH,H2O,andY-sitevacancies.Thereadershouldbeawareoftheseuncertaintiesinthefollowingdiscussion.Somecasesmaybeanalyzed:

1)Ifthesumofcationvalencesisgreaterthan13.5,OwillnecessarilybethedominantspeciesattheYsite,forreasonsofchargebalance.

2)IfFexceeds0.5apfu,FwillbeconsideredasthedominantspeciesattheYsite.Theunderlyingassump-tionisthatFordersatY,whichmaynotbecorrectineverycase.Asubsetofdataconsistingof32oxyfluoridepyrochloreswas considered separately byChakou-makos(1984)todetermineifanyoneofthreepossibleanion configurationswould yield better calculatedvaluesofthecelledgeascomparedwiththeobservedvalues.Thethreeanionconfigurationsconsideredwere:(1)A2B2(O6F),OandFdisorderedoverX andY; (2)A2B2(O5F)O,OandFdisorderedoverX,andOatY,and(3)A2B2X6Y,fullyorderedwithOatXandFatY.

Theregressionstatisticsforthecalculatedversustheobservedcell-edgeforthesethreecaseswerenotsignifi-cantly different.Although arguments of electrostaticneutrality and calculations ofMadelung energy rankthe fully ordered case as themost likely distributionofanions,thecelledgedoesnotappeartobesensitive


enough todistinguish among the three configurationsofanions.

3) If the sumof cation valences is less than 13.5andFis less than0.5apfu,O,OH,F,H2Oor□canbethedominantspeciesattheYsite.Forexample,anNa-dominantmicrolite samplewithavalencesumofcationsequalto12.72mayhaveaformulaendingwith…O6.00(□0.45F0.37O0.17)S1.00,…O6.00[(H2O)0.45F0.37O0.17]S1.00,…O6.00[F0.37(OH)0.35□0.28]S1.00, or…[O5.72(OH)0.28]S6.00[(OH)0.63F0.37]S1.00.The name ofthisspecieswouldbekenonatromicrolite,hydronatro-microlite,fluornatromicrolite,orhydroxynatromicrolite,respectively.All theseoptionsmaybeequallycorrectwithoutadditional information.If,forsomereason, itis not possible to know the dominant species of thedominantvalenceattheY site,wesuggestthatanamewiththeanionprefixsuppressed,suchas“natromicro-lite”beapplied.

Thenewnomenclaturesystem,therefore,resultsinmineralnamesofthetype:

yaroot

whererootisthenameofthegroup,determinedbythedominantspeciesofthedominant-valencegroupattheBsite,yindicatesthedominantspeciesofthedominant-valencegroupattheYsite,andaindicatesthedominantspeciesofthedominant-valencegroupattheAsite.

CalCulaTiOnOfTHefOrMula

Basis for formula calculation

VacanciescanoccuratanyoftheA,XandY sites,buthavenotbeenfoundtooccurattheB site.Conse-quently,pyrochlore formulae shouldbe calculatedonthebasisofanidealnumberofBcations(2apfu).Seethesectionentitled“Theformula”foralistoftypicalB-sitecationstobeusedinthenormalization.

The Si content

Pyrochlore-supergroupmineralsthatexhibithighSicontentsarefairlycommoningeochemicallyevolvedparageneses.The presence and structural role of Siin the structure of pyrochlore-supergroupmineralshave been longdebated but have beenonly partiallyresolved.DifferentexplanationshavebeeninvokedtoclarifythewayinwhichSiisincorporatedintonaturalpyrochlores,includingthepresenceofSiasadispersedcrystallineoramorphoussilicatephase(Hogarth1977,Hogarth&Horne1989,Voloshinet al.1989),anditspresenceasanessentialpartofthestructure.DespitetheabsenceoftetrahedralsitessuitableforSiincorporationin the pyrochlore structure, octahedralSi is possible:Si(OH)62–isstableatlowpressureandtemperatureinthaumasite,Ca3[Si(OH)6][SO4][CO3]•12H2O(Edge&

Taylor 1971).The real restriction on the occurrenceof[6]Siincrystalstructuresisthecrowdingofcationsaroundoxygen ions (O’Keeffe&Hyde1981).UsingTEM–EDX investigations combinedwith crystal-chemicalconsiderations,Bonazziet al.(2006)showedthatasignificantfraction(30–50%)oftheSidetectedbyEMPAdoes in fact occupy theoctahedral sites ofthe pyrochlore structure,whereas a larger fraction(50–70%)ofSi is concentrated in radiation-damagedportionsofthesample.Onthebasisofthisobservation,wecouldperhapsrecommendthatinthecalculationofaformula,nomorethan50%SibeattributedtoB.Never-theless,weprefernorecommendationonhowtoallotSi.TheincorporationornotofSiintothepyrochlore-supergroupmineral structure should be investigated,butlowSicontentscanbeincludedasaB-sitecationorassumedtobeduetocontaminantphases,andthisprobablywill notmodify the name of themineral.Syntheticpyrochlore-likephaseshavealsobeenshowntocontainSi at theB site (Reidet al. 1977).Resultsof two chemical analyses of pyrochlore-supergroupminerals presented byUheret al. (1998) showSi asthedominantcationofthedominantvalenceatB.Ifitisprovedthatall theanalyzedSiisreallyat thissite,thenanewpyrochloregroupwillexistandanewrootnamewillhavetobecreated.

The content of Cs, Rb and K

For stereochemical reasons, thevery largeCs,RbandKcationsprefer the8b (Y) site.TheyshouldnotbeassignedtotheA positionoftheformula.Chemistsrefertopyrochlore-supergroupmineralswithveryhighnumbersofvacanciesatAandabundantCs,RbandKatY as “inverse pyrochlores” (Ercitet al. 1993).NomineralwithapredominanceofthesecationsatYhasbeendescribed.

The content of F, OH and H2O

Themaximum amount ofH2O in the pyrochlorestructure iscontrolledby thecationoccupancyof theA site;themaximumcontentofH2Orangesfrom1.00H2Opfuforidealpyrochlores(twoAcationspfu, i.e., m =0)to1.75H2OpfuforA-deficientpyrochlores(noAcations,i.e.,m=2;Ercitet al.1994).LowA-sitecationcontent, high displacement-parameters for theY-siteconstituents, and the site splitting observed in somecasesfortheYsiteindicatethatthe“O”attheY sitescanbeH2O.Ercitet al.(1994)foundthatH2Omoleculeswereactuallydisplacedawayfromtheideal8bY sites,and partially occupied higher-multiplicity positionsnearby.Displacementsattained0.57Åalongapproxi-mate<112>directionsto96gY’,orasimilardistancealong<111>to32eY”positions.A192iposition(Y’’’)very close toY’was also located by Philippo et al.


(1995). Such displacements allow optimal distancesbetweenA-andY-sitespeciestobemaintained.

ForanormalpyrochloreAB2X6Y,inwhichAandBarecations,andXandYareanions,therearenostereo-chemicalconstraintsonthemaximumoccupanciesoftheAandYsites.However,forpyrochlore-supergroupminerals with H2O at both theA andY sites, themaximumoccupanciesofbothsitesarelimitedowingtotheshortseparationbetweentheidealAandY sites,which is in the neighborhood of 2.3Å (Ercit et al.1994). Partial occupancyof theA site andpositionaldisorder ofH2OatA and Y sites permit stableO...OseparationsforneighboringH2Ogroupsinpyrochlore.Ercitet al.(1994)foundthatpositionaldisorderresultedin eight fractionally occupiedA’ sites around eachA site,displacedfromtheidealsitebyabout0.11Åalong<111>directions.FiveoftheeightaretooclosetotheoffsetY’ andY” positions to represent stableO...OseparationsforH2Ogroups;however,threeoftheeightaresufficientlydistanttorepresentstableintermoleculardistances (averaging 2.74Å). Philippo et al. (1995)reportedadifferentschemeofdisplacement,inwhichH2Opartially occupiesA” sites displaced fromA by0.75Åalong<100>.ForsyntheticA-cation-freepyro-chlore,themaximumH2Ocontentpfumaybelimitedby the need to avoid closeH2O ...H2Odistances: ifthereisoneH2OgrouppfuattheY site,thentherecanbeonly3/8H2Ogroupsat theA site.Thisconstrainttranslatestoamaximumof1.75H2OpfuforA-cation-freepyrochlore.PreviousrefinementsofthestructuresofH2O-bearing pyrochlore have shownH2Oonly inthevicinityoftheY site(e.g.,Groultet al.1982).AsnosyntheticornaturalpyrochlorehasbeenfoundwithallH2OorderedatA,wepresumethattheY siteanditsdisplacedvariantsarethepreferredlocationsforH2O,andthatH2OonlyenterstheA sitesifY cannotaccom-modatemoreH2O.ThemaximumamountofH2Opfuinthepyrochlorestructureisthusgivenas1+(3m/8).ForanidealpyrochlorewithfullA-siteoccupancies(m=0),therecanbenomorethan1H2Opfu;asdescribedabove, the limit for A-deficientpyrochlore (m=2) is1.75H2Opfu(Ercitet al.1994).

If there is a large deficit of cations atA and theanalyticaltotalisverylow,wecouldsuspectthepres-enceofH2OatAsitesofthemineral.Wecancalculatethemaximumpossible amount of structuralH2O inthemineralandcompareitwiththeanalyticaldeficitsinEPMAdata.ButoneshouldneitherassumethatallH2Oinactinide-bearing,radiation-damagedpyrochlore-supergroupminerals is structural, nor that analyticaldeficits in EPMA data for pyrochlore-supergroupminerals are attributable to structuralH2O.Much oftheH2O inmetamict or semi-metamict pyrochlore-supergroupmineralsisadsorbed,andthusnotstructural.Inthisregard,itisinterestingtonotethatchemicaldata

ongeologicallyyoung,non-metamictU-richpyrochlore(Hogarth&Horne1989) indicate lowH2Ocontents.If theH2O content has been established directly andaccurately,e.g.,byTGA,thenitmayindeedbeshownthatsomeH2OmustoccupytheA sites.Unfortunately,wecannotmonitorthecontentofaneutralspeciesotherthanbydensitymeasurements,or fromdeterminationoftheelectrondensityinastructure,neitherofwhichwouldbevery accurate in thepresenceof significantheavy atoms. For nomenclature purposes, itwill beimportant to know theH2O content inA only if thetotalnumberofanyvalencegroupofA-sitecationsisexceededby the zero-chargegroup.Twopossibilitiesexist:(1)thecationdeficitiscomprisedmainlyofH2O,and(2)thedeficitmainlyinvolvesactualsite-vacancies.Ifitisnotpossibletoprovewhichofthetwoscenariosis correct, the expression “zero-valence-dominantspecies”canbeused.

naMeSOfPYrOCHlOre-SuPerGrOuPSPeCieS

The new names are presented below, in groupsdistinguished by the dominantB cation. For eachgroup, a table is shown indicating the combinationsof dominant species of the dominant-valence groupat theA site and dominant species of the dominant-valencegroupattheY siteforwhichthereisevidenceof amineral.With each table, a series of referencesis given for the corresponding species or potentialspecies. Complete descriptions aremissing for themajority of the pyrochlore-supergroup species.Thesevennamesmarkedwithanasterisk(*)refertovalidmineralspeciesbecauseoftheircompletedescriptions.Fluornatromicrolite is an IMA-approvedmineral, butthe complete description has not yet been published.Theother20names refer tominerals thatneed tobecompletelydescribedinordertobeapprovedasvalidspecies.For these, thereareonlychemicalorcrystal-structuredata.Typespecimensneedtobedefinedanddeposited inpublicmineralogicalmuseums.Potentialcandidates for several other species exist, but arenot characterizedwell enough for anyofficial status.Ancientchemicaldataderivedbywet-chemicalanal-ysescommonlyrepresentamixtureofminerals.Thesedatawerenotusedhere.Alldatausedwereacquiredby electron-microprobe analysis or were obtainedby crystal-structure refinements.We also verifiedthe scarcity of crystal-chemical data in the literature.Crystal-structure determinationweremade for onlynine pyrochlore-supergroupminerals.The names ofthesespeciesaremarkedwithadagger(†)inthetables.Aseriousproblemisidentifiedwiththeroméite-groupminerals,becauseofanerroneousassumptionthatalltheSbispentavalent.


Minerals of the pyrochlore group (Table 1)

In the listings that follow, the name attributedby the author or authors isshownissquarebrackets.

fluornatropyrochloreP.M.Kartashov(unpublisheddata)

oxynatropyrochloreHogarth&Horne(1989):anal.3[uranpyrochlore]isoxynatropyrochlore;anal.1,2and4[uranpyrochlore],5and6[uranoanpyrochlore]are“natropyrochlore”.Knudsen (1989): at least three reported compositions are oxynatropyrochlore[pyrochlore].Chukanovet al.(1999):theformulaonpage41[bismutopyrochlore].

hydroxycalciopyrochloreBonazziet al.(2006)[pyrochlore]:onlybycrystal-structurestudywasitpossibletoconfirmahydroxycalciopyrochlorecomposition.

fluorcalciopyrochloreThereareseveralexamplesofanalyzedfluorcalciopyrochlore[pyrochlore]intheliterature,e.g.,Hogarth(1961),Ohnenstetter&Piantone(1992),Nasraouiet al.(1999),Nasraoui&Bilal(2000),Seifertet al.(2000),Thompsonet al.(2002),Leeet al.(2006).ThecrystalstructureoffluorcalciopyrochlorewasdeterminedbyBonazziet al.(2006).

oxycalciopyrochloreThereareseveralexamplesofanalyzedoxycalciopyrochloreintheliterature,e.g.,Hogarth(1961),Černýet al.(1979)[thetype“stibiobetafite”],Williams(1996),Chukanovet al. (1999) [formulaonpage40],Mokhovet al. (2008) [Moon].Thetypespecimenof“stibiobetafite”describedbyČernýet al.(1979)shouldbeconsideredasthetypespecimenofoxycalciopyrochlore.


fluorstrontiopyrochloreFranchini et al. (2005): The “strontiopyrochlore” Ja–13 (first point) isfluorstrontiopyrochlore.

oxyplumbopyrochloreVoloshin&Pakhomovskiy(1986),theiranal.1,Table3.1.

kenoplumbopyrochloreVoloshin&Pakhomovskiy(1986),theiranal.20,Table3.1.

oxyyttropyrochlore-(Y)Tindle&Breaks(1998):sample96–29.

fluorkenopyrochloreKartashovet al.(1998):“strontiopyrochlore”4,and“ceriopyrochlore”8.Schmittet al.(2002):AM206Pclg1–s2rim.

hydropyrochloreThetypesampleof“kalipyrochlore”ofvanWambeke(1978)andthatofErcitet al. (1994)[crystalstructuredetermined]arehydropyrochlore.Thetypespecimenof“kalipyrochlore”describedbyvanWambeke(1978)shouldbeconsideredasthetypespecimenofhydropyrochlore.

Notethatpotentialcandidatesfor“fluorhydropyrochlore”exist[Nasraoui&Bilal(2000),thefirst“kalipyrochlore”andthefirst“ceriopyrochlore”samplesoftheirTable4;Xieet al.(2006),grain1Pyc–Iandgrain3Pyc–I)]

Minerals of the microlite group (Table 2)


fluornatromicroliteThe IMAproposal 98–018 for fluornatromicrolite (Witzke et al. 1998)wasapproved,butthecompletepaperisonlynowinpress.SomedatawerepublishedbyAtencio(2000).ChemicalcompositionsthatcorrespondtofluornatromicrolitefromotheroccurrencesareavailableinthepapersbyOhnenstetter&Piantone(1992),Belkasmiet al.(2000),Huanget al.(2002)andBaldwinet al.(2005).

fluorcalciomicroliteThere are several compositions of fluorcalciomicrolite in the literature, e.g.,Lumpkinet al.(1986),Baldwin(1989),Ohnenstetter&Piantone(1992),Tindle&Breaks(1998),Huanget al.(2002),Geisleret al.(2004),Tindleet al.(2005).

oxycalciomicroliteČernýet al.(2004)[stibiomicrolite];Guastoniet al.(2008)[microlite].

oxystannomicroliteVorma&Siivola(1967)[sukulaite];Ercitet al. (1987)[stannomicrolite].Thetypespecimenof“sukulaite”describedbyVorma&Siivola(1967)shouldbeconsideredasthetypeforoxystannomicrolite.

kenoplumbomicroliteBindiet al.(2006b):crystal-structurestudyofkenoplumbomicrolite.

oxystibiomicroliteGroatet al.(1987):thetypesampleof“stibiomicrolite”;Novák&Černý(1998).Thetypespecimenof“stibiomicrolite”describedbyGroatet al.(1987)shouldbeconsideredasthetypespecimenofoxystibiomicrolite.

hydrokenomicroliteM.B.Andrade&D.Atencio(unpublisheddata).

hydromicroliteM.B.Andrade&D.Atencio(unpublisheddata).

hydroxykenomicroliteErcitet al.(1993):crystal-structurestudyof“cesstibtantite”.Thetypespecimenof“cesstibtantite”describedbyVoloshinet al.(1981)shouldbeconsideredasthetypespecimenofhydroxykenomicrolite.


Minerals of the betafite group (Table 3)

oxycalciobetafiteMeyer&Yang (1988) [yttrobetafite-(Y)]: noH2O reported in the analyticalresults,asthisisalunarmineral;Brugger&Gieré(1999);Cámaraet al.(2004):crystalstructuredetermined.

oxyuranobetafiteMokhovet al.(2008),fromtheMoon.

Minerals of the roméite group (Table 4)


fluornatroroméiteMatsubaraet al.(1996):crystalstructuredetermined.

hydroxycalcioroméiteRouseet al. (1998) andZubkova et al. (2000): crystal structure determined[“lewisite”].Thetypespecimenof“lewisite”describedbyHussak&Prior(1895)shouldbeconsideredasthetypespecimenofhydroxycalcioroméite.

fluorcalcioroméiteBruggeret al.(1997),Uheret al.(1998),Brugger&Gieré(1999).

oxycalcioroméiteChristy&Gatedal(2005).

oxyplumboroméiteChristy&Gatedal(2005)[bindheimite].

Minerals of the elsmoreite group (Table 5)

hydrokenoelsmoreiteSchaller (1911) [“ferritungstite”]; Sahama (1981) [“alumotungstite”];Ercit&Robinson(1994)[“ferritungstite”]:crystalstructuredetermined;Williamset al.(2005)[“elsmoreite”].Thetypespecimenof“elsmoreite”describedbyWilliamset al.(2005)shouldbeconsideredasthetypespecimenofhydrokenoelsmoreite.

COrreSPOnDenCeBeTweenOlDanDnewnaMeS

Allthefollowingmineralnamesshowninitalicsshouldbediscarded,astheydonotcorrespondtodistinctspeciesinthenewclassification.Notethatthereisnotaone-to-onecorrelationbetweenthenewnamesandthetraditionalnamesintheliterature.


Kalipyrochlore

KalipyrochloreofvanWambeke(1978) is insufficientlyK-rich towarrant thename “kalipyrochlore”.The type sample and that of Ercit et al. (1994) areexamplesofhydropyrochlore,withH2OdominantatboththeAandY sites.Addi-tionaldataforsamplesfromthetypeoccurrencearegivenbyWallet al.(1996).

Strontiopyrochlore

Strontiopyrochlore of Lapin et al. (1986), Lottermoser&England (1988),Voloshinet al.(1989),Wallet al.(1996),Kartashovet al.(1998),Chakhmou-radian&Mitchell(1998,2002),andFranchiniet al.(2005)[exceptfluorstron-tiopyrochlore]areCa-orzero-valent-dominantpyrochlore.

Bariopyrochlore

BariopyrochloreofJägeret al.(1959)[“pandaite”],Knudsen(1989),Wallet al.(1996),Williamset al.(1997),Subbotin&Subbotina(2000),andBindiet al.(2006a)areallzero-valent-dominantpyrochlore.

Plumbopyrochlore

Plumbopyrochlore of Skorobogatova et al. (1966),Kartashov et al. (1992),Voloshinet al.(1993),Kovalenkoet al.(1995),andXieet al.(2006)is“plum-bopyrochlore”. Plumbopyrochlore of Chakhmouradian&Mitchell (2002),Wanget al. (2003), andBeurlenet al. (2005) is zero-valent-dominant pyro-chlore.PlumbopyrochloreofVoloshin&Pakhomovskiy(1986)correspondstooxyplumbopyrochlore [their anal. 1,Table 3.1], kenoplumbopyrochlore [theiranal.20,Table3.1]and“plumbopyrochlore”[severalcompositions].

Bismutopyrochlore

BismutopyrochloreofChukanovet al. (1999)andErcitet al. (2003) is zero-valent-dominantpyrochlore.

Ceriopyrochlore-(Ce)

Ceriopyrochlore-(Ce) ofWeidmann&Lenher (1907), vanWambeke (1980),Wallet al.(1996),Chakhmouradian(1996),andZurevinski&Mitchell(2004)isCa-orzero-valent-dominantpyrochlore.

Yttropyrochlore-(Y)

Yttropyrochlore-(Y)ofKalita(1957)[“obruchevite”],andErcitet al.(2003)isazero-valent-dominantmineral.Yttropyrochlore-(Y)ofTindle&Breaks(1998)isoxyyttropyrochlore-(Y).

Uranpyrochlore

Forall recordedcasesofuranpyrochlore,U isnot thedominantcationof thedominantvalenceatA,exceptforsample9fromKhibinastudiedbyChakhmou-radian&Mitchell (2002).Nevertheless, it is not possible to know the domi-nant anionof thedominantvalenceat theY siteof thismineral. It shouldbereferredas“uranopyrochlore”.UranpyrochloreofHogarth&Horne (1989) is“natropyrochlore”.

Stannomicrolite

ThestannomicrolitespeciesofErcitet al. (1987)[“sukulaite”ofVorma&Siivola(1967)]isoxystannomicrolite.ThestannomicroliteofUheret al.(2008)isCa-orzero-valent-dominantmicrolite.


Plumbomicrolite

The plumbomicrolite of Safiannikoff& vanWambeke (1961), Beurlen et al. (2005) andUher et al. (2008) is zero-valent-dominantmicrolite. Theplumbomicrolite ofBindi et al. (2006b) is, by crystal-structure refinement,kenoplumbomicrolite.

Stibiomicrolite

The type sample for stibiomicrolite (Groatet al. 1987) and also the sampleofNovák&Černý(1998)arenowtobeclassifiedasoxystibiomicrolite.TwocompositionsbyČernýet al.(2004)areoxycalciomicrolite,andoneis“calcio-microlite”.ThestibiomicroliteofBeurlenet al.(2005)iszero-valent-dominantmicrolite.

Bismutomicrolite

Thecompositionclaimedfortheoriginalbismutomicrolite[“westgrenite”](vonKnorring&Mrose 1963) probably refers to amixture.Thebismutomicrolitestudied byErichsendeOliveiraet al. (1970) andTindle&Breaks (1998) iszero-valent-dominantmicrolite.

Bariomicrolite

ThebariomicrolitespeciesofHogarth(1977),the“rijkeboerite”ofvanderVeen(1963),istoopoorinBatowarrantthisname.Thetypesampleapparentlyhas□dominantattheApositionandH2OattheYposition,andassuchisprob-ablyhydrokenomicrolite.ThebariomicrolitestudiedbyBeurlenet al.(2005)isprobablyalsohydrokenomicrolite.

Uranmicrolite

Nosamplesdescribedasuranmicrolite(“djalmaite”ofGuimarães1939)(e.g.,Baldwin1989,Rubet al.1998,Tindle&Breaks1998,Novák&Černý1998,Zhanget al.2004,Breiteret al.2007,vanLichterveldeet al.2007,Uheret al.2007)arerichenoughinUtowarrantastatusasaseparatespecies.

Cesstibtantite

Cesstibtantitewas described originally atVasinMyl’kMountain inVoronieTundry,theKolaPeninsula,Russia,byVoloshinet al.(1981).Otheroccurrenceswere described inManitoba,Canada, byErcitet al. (1985), atMt.Holland,Australia,byNickel&Robinson(1985),andatUtö,Sweden,bySmedset al.(1999).ThecrystalstructureofcesstibtantitefromVasinMyl’kMountainandManitobawas solvedbyErcitet al. (1993).Both arenow tobe classified ashydroxykenomicrolite.The two other samples are also zero-valent-dominantmicrolite,butitisnotpossibleprovethattheyarehydroxykenomicrolite.

Natrobistantite

NatrobistantitestudiedbyVoloshinet al.(1983)andbyBeurlenet al.(2005)arebothzero-valent-dominantmicrolite.

Calciobetafite

Hogarth(1977)definedbetafiteasauranium-richTi-dominantpyrochlore,hencethe origin of calciobetafite, a calcium-dominantTi-rich pyrochlore (Mazzi&Munno1983).However, all publishedanalyticaldataon (non-defect) betafitehaveCainexcessofU[exceptthemineralfromtheMoonstudiedbyMokhovet al.(2008)(oxyuranobetafite)];consequently,bycurrentstandards,betafiteisdefinedas a calcium-richandTi-dominantpyrochlore.This renders thename


calciobetafite redundant,andhas theaddedeffectofbringingmembersof thebetafitegroupinlinewiththeothergroups(furthermore,typecalciobetafiteisNb-dominant,notTi-dominant,andbelongstothepyrochloregroup).

Stibiobetafite

Černý et al. (1979) defined stibiobetafite as the Sb3+ analogue of betafite;however,thetypesamplehasNb+Ta>Tiapfu,andCaisthedominantspeciesofthedominant-valencegroupattheAsite.Thetypesampleisnowtobeclassifiedasoxycalciopyrochlore.ItisnotpossibletocalculatetheformulaofstibiobetafitestudiedbyTindle&Breaks(1998)owingtoerrorsinthetableofanalyticaldata.

Plumbobetafite

Plumbobetafite ofGanzeevet al. (1969) is zero-valent-dominant pyrochlore.PlumbobetafiteofVoloshinet al.(1993)is“plumbobetafite”.

Yttrobetafite-(Y)

Yttrobetafite-(Y)ofKalita (1959)andLiferovich&Mitchell (2005)arezero-valent-dominantpyrochlore.Yttrobetafite-(Y) fromtheMoon(Meyer&Yang1988)isoxycalciobetafite.

Lewisite

Crystal-structure studies (Rouse et al. 1998, Zubkova et al. 2000) proved“lewisite”tobehydroxycalcioroméite.

Stetefeldtite

Veryoldreferences(Riotte1867,Mason&Vitaliano1953).Probably“argento-roméite”.Thismaterialneedstobeexaminedchemicallyandstructurally.

Stibiconite

Originalmaterial describedbyBeudant (1837).Probably “stibioroméite”.Noelectron-microprobe data are available.Thismaterial needs to be examinedchemicallyandstructurally.

Bindheimite

OriginalmaterialdescribedbyDana (1868).Onlywith thedataofChristy&Gatedal(2005)isitpossibletocorrelatethismineralwithoxyplumboroméite.

Monimolite

Theproblematicalspeciesmonimolite(Igelström1865,Mason&Vitaliano1953)isalmostcertainlyidenticalwithoxyplumboroméite,butneedsre-examination.

Bismutostibiconite

ThemineralwasdescribedbyWalenta (1983).Thechemicaldataareconsid-eredinadequateowingtoastandardlessenergy-dispersionspectroscopy(EDS),withallSbassumedtobe5+,andresultsoftheanalysisnormalizedto100%.Itprobablyis“bismutoroméite”.Needsachemicalandstructuralinvestigation.

Partzite

Arents (1867). Probably “cuproroméite”.No electron-microprobe data.Thismaterialneedstobeexaminedchemicallyandstructurally.


Ferritungstite and alumotungstite

Ferritungstite (Schaller 1911, Ercit&Robinson 1994) and alumotungstite(Sahama1981)arehydrokenoelsmoreite.

Jixianite

Jixianite(Liu1979)is“plumboelsmoreite”.Intheabsenceofacrystal-structurestudy,itisnotpossibletoknowthedominantanionofthedominantvalenceattheYsiteofjixianite.

THefOrMulaOfSeleCTeDSPeCieS

Formulae are given inTable 6 for all 28 pyrochlorespecies forwhichwehave analytical evidence.Notethat subordinatecomponentsat theA,B,XorY siteshavenonomenclaturalsignificance.Weshowspecificexamplesherethataretypicaloftheminorcomponentsobserved, but anyof these couldbe replacedby “#”,indicatinganunspecifiedheterovalentspeciesrequiredforchargebalance.

inDexOfMineralnaMeS

We show in Table 7 the correspondence betweenpublishednames(withreferences)andthenewnamesproposed,withanindicationoftherecommendedfateoftheoldname.

aCKnOwleDGeMenTS

WeacknowledgeStuartMills,DanaGriffen,BillBirch,FrédéricHatert,ErnstBurke,RobertF.Martin,AndreyBulakhandallmembersoftheIMACommis-sion onNewMinerals,Nomenclature andClassifi-cation for their helpful suggestions and comments,and FAPESP (Fundação deAmparo à Pesquisa doEstadodeSãoPaulo) forfinancialsupport (processes2008/04984–7and2009/09125–5).

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Received June 12, 2010.

Documents

the pyrochlore supergroup of minerals: nomenclature