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Pyrochlore Supergroup

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About Pyrochlore SupergroupHide

Formula:
A2-mD2X6-wZ1-n
A typically is a large [8]-coordinated cation with a radius of ~1.0 Å or a vacancy (□), but can also be H2O.

The A site, therefore, may host Na, Ca, Sr, Pb2+, Sn2+, Sb3+, Y, U, □, or H2O or, less frequently Ag, Mn, Ba, Fe2+, Bi3+, Ce (and other REE), Sc or Th.

D is a [6]-coordinated cation typically of high field-strength. This site thus may contain Ta, Nb, Ti, Sb5+ or W, but also V5+, Sn4+, Zr, Hf, Fe3+, Mg, Al and Si. DX6 edge-sharing octahedra form a framework, in which the cavities host the A cations.

X typically is O but can include subordinate OH and F.

Z typically is an anion, but can also be a vacancy, H2O, or a very large (>> 1.0 Å) monovalent cation (site 8b). Examples are OH, F, O, □, H2O, K, Cs, Rb.

The symbols m, w, and n represent parameters that indicate incomplete occupancy of the A, X and Z sites, respectively. Vacancies have not been found to occur at the D site (Atencio et al. 2010).

Note: the D group is named as B in the paper above, and the Z group is named as Y. These are renamed here to avoid confusion with Boron and Yttrium respectively.
Name:
The supergroup has its name after the generic name pyrochlore. The name was first introduced by J. J. Berzelius for a cubic mineral found by N.O.Tank in the 1820s in a syenite pegmatite at Stavern (formerly Fredriksvärn), Norway (Wöhler 1826). It is derived from the Greek πΰρ, fire, and χλωρός, green in allusion to the fact that the mineral usually turns green on ignition.
In 1977 Hogarth introduced a new classification of the "pyrochlore group". This system did not entirely fit the current IMA rules for mineralogical nomenclature. The nomenclature was therefore revised by Atencio et al. (2010); see also Christy & Atencio (2013), and approved by IMA.
The pyrochlore supergroup is a group of chemically complex cubic oxides. The classification of the pyrochlore supergroup is based on the ions at the A, B and Y sites.
A correct identification of individual members is only possible using a combination of several analytical methods.
The pyrochlore supergroup is divided into five groups based on the atomic proportions of the B-site atoms, Nb, Ta, Sb, Ti and W: Pyrochlore Group, Microlite Group, Roméite Group, Betafite Group and Elsmoreite Group. Additional groups (Ralstonite Group, Coulsellite Group) were established subsequently (Atencio et al., 2017).

NB: The pyrochlore supergroup is broader and includes more minerals than the historically "pyrochlore group". The later is also not identical with the new subgroup, pyrochlore group.

00503700014946348649806.jpg
Fluornatropyrochlore, Pyrochlore Group
07893700014946348641745.jpg
Cuproroméite, Roméite Group
00255800014946348654351.jpg
Oxyuranobetafite, Betafite Group
01862050014946348659332.jpg
Hydrokenoelsmoreite, Elsmoreite Group
09554760015037224014712.jpg
Fluornatropyrochlore, Pyrochlore Group
04704390014954282913276.jpg
Cuproroméite, Roméite Group
01302400014968640542874.jpg
Oxyuranobetafite, Betafite Group
01590760014962761733797.jpg
Hydrokenoelsmoreite, Elsmoreite Group
04008780014946348651863.jpg
Fluornatropyrochlore, Pyrochlore Group
02260370014946348662384.jpg
Cuproroméite, Roméite Group
00984100014946348801635.jpg
Oxyuranobetafite, Betafite Group
07409870014960843015299.jpg
Hydrokenoelsmoreite, Elsmoreite Group


The names of each member of the pyrochlore supergroup are composed of the group name plus two prefixes:
1. The first prefix refers to the dominant cation or anion of the dominent valance or H2O or vacancy at the Y site: OH = hydroxy-, F = fluor-, O = oxy-, H2O = hydro- and vacancy = □.

2. The second prefix refers to the dominant cation of the dominant valance or H2O or vacancy at the A site. Examples: Sr = strontio, Na = natro, Pb = plumbo.
When the first and second prefixes are equal, only one prefix is applied (Atencio et al., 2010).


Classification of Pyrochlore SupergroupHide

Notes:
IMA Approved Group Name

Chemical Properties of Pyrochlore SupergroupHide

Formula:
A2-mD2X6-wZ1-n

A typically is a large [8]-coordinated cation with a radius of ~1.0 Å or a vacancy (□), but can also be H2O.

The A site, therefore, may host Na, Ca, Sr, Pb2+, Sn2+, Sb3+, Y, U, □, or H2O or, less frequently Ag, Mn, Ba, Fe2+, Bi3+, Ce (and other REE), Sc or Th.

D is a [6]-coordinated cation typically of high field-strength. This site thus may contain Ta, Nb, Ti, Sb5+ or W, but also V5+, Sn4+, Zr, Hf, Fe3+, Mg, Al and Si. DX6 edge-sharing octahedra form a framework, in which the cavities host the A cations.

X typically is O but can include subordinate OH and F.

Z typically is an anion, but can also be a vacancy, H2O, or a very large (>> 1.0 Å) monovalent cation (site 8b). Examples are OH, F, O, □, H2O, K, Cs, Rb.

The symbols m, w, and n represent parameters that indicate incomplete occupancy of the A, X and Z sites, respectively. Vacancies have not been found to occur at the D site (Atencio et al. 2010).

Note: the D group is named as B in the paper above, and the Z group is named as Y. These are renamed here to avoid confusion with Boron and Yttrium respectively.

Synonyms of Pyrochlore SupergroupHide

Varieties of Pyrochlore SupergroupHide

Betafite (of Hogarth 1977)True "Betafite" samples are structurally members of the pyrochlore supergroup. Hogarth (1977) stated that the betafite group has 2Ti ≥ (Nb + Ta), however the formulae of most betafites do not exactly correspond to pyrochlores and that difference has del...
Mendeleevite (of Vernadsky 1914)Regarded by Hogarth (1977) as synonymous with betafite (of Hogarth 1977), but more recent analysis (see https://www.mindat.org/mesg-494971.html) classified it as Uranpyrochlore (of Hogarth 1977). However in the newer classification (Atencio, et al. 2017) ...
Plumbobetafite (of Hogarth 1977)Plumbobetafite of Ganzeev et al. (1969) is a Zero valent dominant member of the Pyrochlore Group. Plumbobetafite of Voloshin et al. (1993) is a "plumbobetafite".
Stibiobetafite (of Černý et al.)Černý et al. (1979) defined stibiobetafite as the Sb3+ analogue of betafite; however, the type sample has Nb + Ta > Ti apfu, and Ca is the dominant species of the dominant-valence group at the A site. The type sample is now to be classified as oxycalcio...
TangeniteAn impure "betafite" (s.l.) enriched with TiO2. Probably a mixture of several phases.

Relationship of Pyrochlore Supergroup to other SpeciesHide

Group Members:
Betafite Group A2(Ti,Nb)2O6Z
  Oxycalciobetafite Ca2(Ti,Nb)2O6O
  Oxyuranobetafite (U,Ca,◻)2(Ti,Nb)2O6O
Coulsellite Group A2-mMg2F6-wF1-n
  Fluornatrocoulsellite CaNa3AlMg3F14Trig. 3m (3 2/m) : R3m
Elsmoreite Group 
  Hydrokenoelsmoreite 2W2O6(H2O)Iso. m3m (4/m 3 2/m) : Fd3m
  Hydroxykenoelsmoreite (□,Pb)2(W,Fe3+,Al)2(O,OH)6(OH)Trig. 3 : R3
Microlite Group A2-mTa2X6-wZ-nIso. m3m (4/m 3 2/m) : Fd3m
  Fluorcalciomicrolite (Ca,Na)2(Ta,Nb)2O6FIso. m3m (4/m 3 2/m) : Fd3m
  Fluornatromicrolite (Na1.5Bi0.5)Ta2O6FIso. m3m (4/m 3 2/m) : Fd3m
  Hydrokenomicrolite (◻,H2O)2Ta2(O,OH)6(H2O)Iso. m3m (4/m 3 2/m)
  Hydromicrolite (H2O,◻)2Ta2(O,OH)6(H2O)
  Hydroxycalciomicrolite Ca1.5Ta2O6(OH)Iso. 4 3 2 : P42 3 2
  Hydroxykenomicrolite (◻,Na,Sb3+)2Ta2O6(OH)Iso.
  Hydroxynatromicrolite (Na,Bi3+,◻)2Ta2O6(OH)Iso. m3m (4/m 3 2/m) : Fd3m
  Kenoplumbomicrolite (Pb,◻)2Ta2O6(◻,OH,O)Iso.
  Oxycalciomicrolite Ca2Ta2O6O
  Oxystannomicrolite Sn2Ta2O6O
  Oxystibiomicrolite (Sb3+,Ca)2Ta2O6O
  Yttromicrolite (of Hogarth) (Ca,Y3+,U,Na)2-x(Ta,Nb,Ti,Fe3+)2O7Iso. m3m (4/m 3 2/m) : Fd3m
Oxybismutomicrolite (Bi1.330.67)Σ2Ta2O6OIso. m3m (4/m 3 2/m) : Fd3m
Pyrochlore Group A2Nb2(O,OH)6Z
  Cesiokenopyrochlore □Nb2(O,OH)6Cs1−x (x ∼ 0.20)Iso. m3m (4/m 3 2/m) : Fd3m
  Fluorcalciopyrochlore (Ca,Na)2(Nb, Ti)2O6FIso.
  Fluorhydropyrochlore 
  Fluorkenopyrochlore (□,Sr,Ce,Ca,Na)2(Nb,Ti)2O6F
  Fluornatropyrochlore (Na,Pb,Ca,REE,U)2Nb2O6FIso. m3m (4/m 3 2/m)
  Fluorplumbopyrochlore (Pb,Y,Th,U,Na,Ca)2-x(Nb,Ti)2O6FIso.
  Fluorstrontiopyrochlore (Sr,□)2Nb2(O,OH)6F
  Hydrokenopyrochlore (□,□)2Nb2O6·H2OIso. m3m (4/m 3 2/m) : Fd3m
  Hydropyrochlore (H2O,□)2Nb2(O,OH)6(H2O)Iso. m3m (4/m 3 2/m) : Fd3m
  Hydroxycalciopyrochlore (Ca,Na,U,□)2(Nb,Ti)2O6(OH)Iso. m3m (4/m 3 2/m) : Fd3m
  Hydroxykenopyrochlore (□,Ce,Ba)2(Nb,Ti)2O6(OH,F)Iso. m3m (4/m 3 2/m) : Fd3m
  Hydroxymanganopyrochlore (Mn2+,Th,Na,Ca,REE)2(Nb,Ti)2O6(OH) Iso. m3 (2/m 3)
  Hydroxynatropyrochlore (Na,Сa,Ce)2Nb2O6(OH)Iso. m3m (4/m 3 2/m) : Fd3m
  Hydroxyplumbopyrochlore (Pb,Ca)2-x(Nb,Ti,Ta)2O6(OH)
  Kenoplumbopyrochlore (Pb,□)Nb2O6(□,O)
  Oxycalciopyrochlore Ca2Nb2O6OIso. m3m (4/m 3 2/m) : Fd3m
  Oxynatropyrochlore (Na,Ca,U)2Nb2O6(O,OH)
  Oxyplumbopyrochlore Pb2Nb2O6O
  Oxyyttropyrochlore-(Y) (Y,◻)2Nb2O6O
  Unnamed (Sb-analogue of Hydroxymanganopyrochlor) (Mn,Ca,Y)2(Sb,Ti)2O6(OH)
Ralstonite Group 
  Hydrokenoralstonite  Na0.5(Al,Mg)2(F,OH)6•H2O Iso. m3m (4/m 3 2/m) : Fd3m
Roméite Group A2(Sb5+)2O6Z
  Cuproroméite Cu2Sb2(O,OH)7Iso.
  Fluorcalcioroméite (Ca,Na,◻)2Sb5+2(O,OH)6FIso. m3m (4/m 3 2/m) : Fd3m
  Hydroxycalcioroméite (Ca,Sb3+)2(Sb5+,Ti)2O6(OH)Iso. m3m (4/m 3 2/m) : Fd3m
  Hydroxyferroroméite (Fe2+1.50.5)Sb5+2O6(OH)Iso. m3m (4/m 3 2/m) : Fd3m
  Oxycalcioroméite Ca2Sb2O6OIso. m3m (4/m 3 2/m) : Fd3m
  Oxyplumboroméite Pb2Sb2O6OIso. m3m (4/m 3 2/m) : Fd3m

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Pyrochlore Supergroup in petrologyHide

An essential component of rock names highlighted in red, an accessory component in rock names highlighted in green.

References for Pyrochlore SupergroupHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Pyatenko, Y.A. (1959) Crystal chemistry and characteristics of minerals of pyrochlore group. Kristallografiya: 4: 204-208 (English abstract).
Hogarth, D.D. (1977) Classification and nomenclature of the pyrochlore group. American Mineralogist: 62: 403-410.
Chakoumakos, B.C. (1984) Systematics of the pyrochlore structure type, ideal A2B2X6Y. Journal of Solid State Chemistry: 53: 120-129.
Greegor, R.B., Lytle, F.W., Chakoumakos, B.C., Lumpkin, G.R., and Ewing, R.C. (1985) An investigation of metamict and annealed pyrochlores by X-ray absorption spectroscopy. In C.M. Jantzen, J.A. Stone, and R.C. Ewing, Eds., Scientific Basis for Nuclear Waste Management VIII: 655-662. Materials Research Society, Pittsburgh.
Lumpkin, G.R., Foltyn, E.M., and Ewing, R.C. (1986) Thermal recrystallization of alpha-recoil damaged minerals of the pyrochlore structure type. Journal of Nuclear Materials: 139: 113-120.
Lumpkin, G.R. and Ewing, R.C. (1988) Alpha-decay damage in minerals of the pyrochlore group. Physics and Chemistry of Minerals: 16: 220.
Lumpkin, G.R. and Ewing, R.C. (1992) Geochemical alteration of pyrochlore group minerals: Microlite subgroup. American Mineralogist: 77: 179-188.
Johan, V. and Johan, Z. (1994) Accessory minerals of the Cinovec (Zinnwald) granite cupola, Czech Republic Part 1: Nb-, Ta-, and Ti-bearing oxides. Mineralogy and Petrology: 51: 323-343.
Lumpkin, G.R. and Ewing, R.C. (1995) Geochemical alteration of pyrochlore group minerals: Pyrochlore subgroup. American Mineralogist: 80: 732-743.
Lumpkin, G.R. and Ewing, R.C. (1996) Geochemical alteration of pyrochlore group minerals: Betafite subgroup. American Mineralogist: 81: 1237-1248.
Hogarth, D.D., Williams, C.T., and Jones, P. (2000) Primary zoning in pyrochlore group minerals from carbonatites. Mineralogical Magazine: 64: 683-697.
Nasraoui, M. and Waerenborgh, J.C. (2001) Fe speciation in weathered pyrochlore-group minerals from the Lueshe and Araxá (Barreiro) carbonatites by 57Fe Mössbauer spectroscopy. The Canadian Mineralogist: 39: 1073-1080.
Chakhmouradian, A.R. and Mitchell, R.H. (2002) New data on pyrochlore- and perovskite-group minerals from the Lovozero alkaline complex, Russia. European Journal of Mineralogy: 14: 821-836.
Atencio, D., Andrade, M.B., Christy, A.G., Gieré, R., and Kartashov, P.M. (2010) The pyrochlore supergroup of minerals: nomenclature. The Canadian Mineralogist: 48: 673-698.
Brik, M.G. and Srivastava, A.M. (2012) Pyrochlore structural chemistry: predicting the lattice constant by the ionic radii and electronegativities of the constituting ions. J. Am. Ceram. Soc. 95, 1454-1460.
Christy, A.G. and Atencio, D. (2013) Clarification of status of species in the pyrochlore supergroup. Mineralogical Magazine: 77: 13-20.
Atencio, D., Andrade, M.B., Bastos Neto, A.C., and Pereira, V.P. (2017) Ralstonite renamed hydrokenoralstonite, coulsellite renamed fluornatrocoulsellite, and their incorporation into the pyrochlore supergroup. Can. Mineral. 55, 115-120.

Internet Links for Pyrochlore SupergroupHide

Localities for Pyrochlore SupergroupHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

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