Pyrochlore

Infobox mineral
name = Pyrochlore
category = Oxide mineral
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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, Gd_1.9Ca_0.1Ti₂O_6.9, metallic conductivity, Bi₂Ru₂O_7-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