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Pyrochlore Group

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Formula:
A2Nb2(O,OH)6Z
A is Na, Ca, Sn2+, Sr, Pb2+, Sb3+, Y, U4+, H2O or ◻.

Z is OH, F, O, H2O or ◻
System:
Isometric
Colour:
Brown, yellow-brown, ...
Hardness:
5 - 5½
Name:
From the Greek πΰρ, fire, and χλωρός, green in allusion to the fact that the mineral usually turns green on ignition.
The nomenclature was recently revised by Atencio et al. (2010) and Christy and Atencio (2013).

Classification of Pyrochlore Group

Redefined Approved 2010
4.00.

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
0 :
0 :
8.2.1.1

8 : MULTIPLE OXIDES CONTAINING NIOBIUM,TANTALUM OR TITANIUM
2 : A2B2O6(O,OH,F)
18.2.8

18 : Niobates and Tantalates
2 : Niobates and tantalates containing rare earths but not U
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Type Occurrence of Pyrochlore Group

Year of Discovery:
1826

Occurrences of Pyrochlore Group

Geological Setting:
Pegmatites in nepheline syenites, granitic pegmatites and greisens, carbonatites.

Physical Properties of Pyrochlore Group

Vitreous, Resinous
Diaphaneity (Transparency):
Transparent
Colour:
Brown, yellow-brown, reddish brown, orange, black
Streak:
Light brown, yellow-brown
Hardness (Mohs):
5 - 5½
Hardness (Vickers):
VHN100=542 - 665 kg/mm2
Tenacity:
Brittle
Cleavage:
Distinct/Good
Octahedral {111} (may be a parting), sometimes distinct but usually not distinguishable.
Fracture:
Irregular/Uneven, Splintery, Sub-Conchoidal
Density:
4.45 - 4.9 g/cm3 (Measured)    4.33 g/cm3 (Calculated)
Comment:
Density increases with uranium content.

Crystallography of Pyrochlore Group

Crystal System:
Isometric
Class (H-M):
m3m (4/m 3 2/m) - Hexoctahedral
Space Group:
Fd3m
Cell Parameters:
a = 10.41(6) Å
Unit Cell Volume:
V 1,128.11 ų (Calculated from Unit Cell)
Z:
8
Morphology:
Crystals octahedral, often with subordinate {011}, {113} or {001}. Irregular masses and embedded grains.
Twinning:
Twin plane {111} (spinel law twins), rare.
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Chemical Properties of Pyrochlore Group

Formula:
A2Nb2(O,OH)6Z

A is Na, Ca, Sn2+, Sr, Pb2+, Sb3+, Y, U4+, H2O or ◻.

Z is OH, F, O, H2O or ◻
Common Impurities:
Fe,Mg,Mn,U,Ta,Ti

Relationship of Pyrochlore Group to other Species

Group Members:
Fluorcalciopyrochlore (Ca,Na)2(Nb, Ti)2O6F
Fluorkenopyrochlore (□,Sr,Ce,Ca,Na)2(Nb,Ti)2O6F
Fluornatropyrochlore (Na,REE,Ca)2Nb2(O,OH)6F
Fluorplumbopyrochlore (Pb,Y,Th,U,Na,Ca)2-x(Nb,Ti)2O6F
Fluorstrontiopyrochlore (Sr,□)2Nb2(O,OH)6F
Hydropyrochlore (H2O,□)2Nb2(O,OH)6(H2O)
Hydroxycalciopyrochlore (Ca,Na,U,□)2(Nb,Ti)2O6(OH)
Hydroxymanganopyrochlore (Mn2+,Th,Na,Ca,REE)2(Nb,Ti)2O6(OH)
Hydroxyplumbopyrochlore (Pb,Ca)2-x(Nb,Ti,Ta)2O6(OH)
Kenoplumbopyrochlore (Pb,□)Nb2O6(□,O)
Oxycalciopyrochlore Ca2Nb2O6O
Oxynatropyrochlore (Na,Ca,U)2Nb2O6(O,OH)
Oxyplumbopyrochlore Pb2Nb2O6O
Oxyyttropyrochlore-(Y) (Y,◻)2Nb2O6O
4.00.Goethiteα-Fe3+O(OH)
4.00.Microlite Group
4.00.Roméite Group
4.00.Písekite-(Y)(Y,As,Ca,Fe,U)(Nb,Ti,Ta)O4
4.00.UM2004-19-O:AlCeGdZr(Gd,Ce)4Al2Zr4O17
4.00.UM2004-21-O:CaFeGdZrCa2Gd4Fe5ZrO15
4.00.UM2004-27-O:GdTiGd2Ti4O11
18.2.1Fergusonite-(Y)YNbO4
18.2.2Fergusonite-(Y)-βYNbO4
18.2.3Fergusonite-(Ce)(Ce,La,Nd)NbO4
18.2.4Fergusonite-(Ce)-β(Ce,La,Nd)NbO4
18.2.5Fergusonite-(Nd)(Nd,Ce)(Nb,Ti)O4
18.2.6Fergusonite-(Nd)-β(Nd,Ce)NbO4
18.2.7Formanite-(Y)YTaO4
18.2.9Ceriopyrochlore (of Hogarth 1977)
18.2.10Strontiopyrochlore (of Hogarth 1977)
18.2.11Loparite-(Ce)(Na,Ce,Ca,Sr,Th)(Ti,Nb,Fe)O3
18.2.12Fersmite(Ca,Y)(Nb,Ta,Ti)2(O,OH)6
18.2.13Aeschynite-(Ce)(Ce,Ca,Fe,Th)(Ti,Nb)2(O,OH)6
18.2.14Aeschynite-(Nd)(Nd,Ce,Ca)(Ti,Nb)2(O,OH)6
18.2.15Aeschynite-(Y)(Y,Ca,Fe,Th)(Ti,Nb)2(O,OH)6
18.2.16Nioboaeschynite-(Ce)(Ce,Ca,Th)(Nb,Ti)2(O,OH)6
18.2.17Nioboaeschynite-(Nd)(Nd,Ce,Ca,Th)(Nb,Ti,Fe,Ta)2(O,OH)6
18.2.18Tantalaeschynite-(Y)(Y,Ce,Ca)(Ta,Ti,Nb)2O6
18.2.19Vigezzite(Ca,Ce)(Nb,Ti)2O6
18.2.20Murataite-(Y)(Y,Na)6Zn(Zn,Fe3+)4(Ti,Nb,Na)12O29(O,F,OH)10F4

Other Names for Pyrochlore Group

Other Information

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

References for Pyrochlore Group

Reference List:
Wöhler (1826), Ann. Pys.: 7: 417.

Rose (1840), Ann. Phys.: 48: 562 (as Pyrrhit).

Knop (1875), Jb. Min.: 67.

Allen (1877), American Journal of Science: 14: 128 (as Hatchettolite).

Smith (1877), American Journal of Science: 13: 365 (as Hatchettolite).

Hubbard (1886), Verh. natur-hist. Ver. preuss. Rheinland, Sitzber.: 43: 217 (as Azor-pyrrhit).

Holmqist (1896), Geological Institute Upsala, Bulletin: 3: 181 (as uranpyrochlore).

Flink (1898), Meddelelser om Grønland: 14: 234 (as chalcolamprite).

Flink (1901), Meddelelser om Grønland: 24: 166 (as Endeiolite).

Gaertner (1930), Jb. Min., Beil.-Bd.: 61: 1.

Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged: 748-756.

Hogarth, D.D. (1961) A study of pyrochlore and betafite. Canadian Mineralogist: 6: 610-633.

American Mineralogist (1977): 62: 403-410.

Hogarth, D.D. (1989) Pyrochlore, apatite and amphibole: distinctive minerals in carbonatite. In K. Bell, Ed., Carbonatites: Genesis and Evolution: 105-148. Unwin Hyman Ltd., London.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (1997) Handbook of Mineralogy, Volume III. Halides, Hydroxides, Oxides. Mineral Data Publishing, Tucson, AZ, 628pp.: 457.

Bonazzi, P., Bindi, L., Zoppi, M., Capitani, G.C., and Olmi, F. (2006) Single-crystal diffraction and transmission electron microscopy studies of "silicified" pyrochlore from Narssârssuk, Julianehaab district, Greenland. American Mineralogist: 91: 794-801.

Birch, W.D., Grey, I.E., Mills, S.J., Bougerol, C., Pring, A., Ansermet, S. (2007): Pittongite, a new secondary tungstate from Pittong, Victoria, Australia. Canadian Mineralogist, 45, 857-864.

Atencio D., Andrade M.B., Christy A.G., Giere R., Kartashov P.M. (2010): The pyrochlore supergroup of minerals: nomenclature. Canadian Mineralogist, 48, 569-594.

Christy, A. G. and Atencio, D. (2013): Clarification of status of species in the pyrochlore supergroup. Mineralogical Magazine, 77, 13-20.

Internet Links for Pyrochlore Group

Localities for Pyrochlore Group

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