Pyrochlore

Pyrochlore

Infobox mineral
name = Pyrochlore
category = Oxide mineral
boxwidth =
boxbgcolor =


caption =
formula = (Na,Ca)2Nb2O6(OH,F)
molweight =
color = Brown, yellow-brown, reddish brown, orange, black
habit = disseminated granular - subhedral
system = Isometric
twinning = 111 rare
cleavage = 111 indestinct
fracture = Subconchoidal to uneven, splintery
mohs = 5.0 - 5.5
luster = vitreous to resinous
polish =
refractive = n = 1.9–2.2
opticalprop = Isotropic, weak anomalous anisotropism
birefringence =
pleochroism =
streak = White
gravity = 4.2 - 6.4
melt =
fusibility =
diagnostic =
solubility =
diaphaneity = Subtranslucent to opaque
other = Variably radioactive

Pyrochlore (Na,Ca)2Nb2O6(OH,F) is a solid solution between the niobium end member (pyrochlore), and the tantalum end member (microlite). The mineral is associated with the metasomatic end stages of magmatic intrusions. Pyrochlore crystals are usually well formed (Euhedral), occurring usually as octahedra of a yellowish or brownish color and resinous luster. It is commonly metamict due to radiation damage from included radioactive elements.

Pyrochlore occurs in pegmatites associated with nepheline syenites and other alkalic rocks. It is also found in granite pegmatitesand greisens. It is characteristically found in carbonatites. Associated minerals include: zircon, aegirine, apatite, perovskite and columbite.

The name is from the Greek πΰρ, "fire", and χλωρός, "green" because it typically turns green on ignition in classic blowpipe analysis.

Pyrochlore is also a more generic term for the pyrochlore crystal structure (Fd-3m). The more general crystal structure describes materials of the type A2B2O6 and A2B2O7 where the A and B species are generally rare-earth or transition metal species; e.g. Y2Ti2O7.The pyrochlore structure is a super structure derivative of the simple fluorite structure (AO2 = A4O8, where the A and B cations are ordered along the <110> direction. The additional anion vacancy resides in the tetrahedral intersticy between adjacent B-site cations. These systems are particularly susceptible to geometrical frustration and novel magnetic effects.

The pyrochlore structure shows varied physical properties ranging from electronic insulators, La2Zr2O7, ionic conductors, Gd1.9Ca0.1Ti2O6.9, metallic conductivity, Bi2Ru2O7-y, Mixed Ionic and Electronic Conductivity, spin ice systems Dy2Ti2O7, spin glass systems Y2Mo2O7 and superconducting materials Cd2Re2O7.

Niobium mining

The three largest producers of niobium ore are mining pyrochlore deposites. The largest deposites in Brazil is the CBMM mine located south of Araxá, Minas Gerais the other deposite is the Catalão mine east of Catalão, Goiás. The other third largest deposite of niobium ore is Saint-Honore mine west of Saint-Honore near Chicoutimi, Quebec.cite web | url = http://tesla.desy.de/new_pages/TESLA_Reports/2001/pdf_files/tesla2001-27.pdf | title = Niob für TESLA | accessdate = 2008-09-02 | author = J. Kouptsidis, F. Peters, D. Proch, W. Singer]

ee also

* List of minerals

References

* [http://webmineral.com/data/Pyrochlore.shtml Webmineral - Pyrochlore]
* [http://mineral.galleries.com/minerals/oxides/pyrochlo/pyrochlo.htm Mineral galleries]
* [http://www.mindat.org/min-3316.html Mindat]
* [http://rruff.geo.arizona.edu/doclib/hom/pyrochlore.pdf Handbook of Mineralogy]
*"Oxide Pyrochlores - A Review", M.A. Subramanian, G. Aravamudan and G. V. Subba Rao, Progress in Solid State Chemistry, Volume 15 (1983) pp. 55-143


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Look at other dictionaries:

  • Pyrochlore — Pyr o*chlore, n. [Pyro + Gr. ? pale green.] (Min.) A niobate of calcium, cerium, and other bases, occurring usually in octahedrons of a yellowish or brownish color and resinous luster; so called from its becoming grass green on being subjected to …   The Collaborative International Dictionary of English

  • pyrochlore — /puy reuh klawr , klohr /, n. a mineral, chiefly composed of niobates of the cerium metals, occurring in syenites in the form of brown crystals. [1820 30; < G Pyrochlor. See PYRO , CHLOR 1] * * * ▪ mineral       a complex oxide mineral [(Na,… …   Universalium

  • pyrochlore — pirochloras statusas T sritis chemija apibrėžtis Mineralas. formulė (Na,Ca)₂(Nb,Ti,Ta)₂O₆(OH,F,O) atitikmenys: angl. pyrochlore rus. пирохлор …   Chemijos terminų aiškinamasis žodynas

  • pyrochlore — ˈpīrəˌklō(ə)r noun ( s) Etymology: German pyrochlor, from pyr + Greek chlōros greenish yellow more at yellow : a brown or dark reddish mineral NaCaCb2O6F that is isomorphous with microlite and is an oxide and fluoride of sodium, calcium, and… …   Useful english dictionary

  • pyrochlore — noun A mineral whose composition is that of a mixed niobate mostly of sodium, calcium and cerium, (Na,Ca)NbO(OH,F) …   Wiktionary

  • pyrochlore — (pi ro klo r ) s. m. Titanate de chaux engagé dans la syénite de Norwége …   Dictionnaire de la Langue Française d'Émile Littré

  • pyrochlore — py·ro·chlore …   English syllables

  • Niobium — zirconium ← niobium → molybdenum V ↑ Nb ↓ Ta …   Wikipedia

  • List of minerals (complete) — It is currently not possible to have a complete list of minerals . The International Mineralogical Association (IMA) is the international group that recognises new minerals and new mineral names. However, minerals discovered before 1959 did not… …   Wikipedia

  • Pyrochlor — Chemische Formel Ca2Nb2O7 [1] Mineralklasse Oxide und Hydroxide 4.DH.15 (8. Auflage: I …   Deutsch Wikipedia

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