My watch list
my.chemeurope.com  
Login  

Pyrochlore



Pyrochlore
CategoryOxide mineral
Chemical formula(Na,Ca)2Nb2O6(OH,F)
Identification
ColorBrown, yellow-brown, reddish brown, orange, black
Crystal habitdisseminated granular - subhedral
Crystal systemIsometric
Twinning111 rare
Cleavage111 indestinct
FractureSubconchoidal to uneven, splintery
Mohs Scale hardness5.0 - 5.5
Lustervitreous to resinous
Refractive indexn = 1.9–2.2
Optical PropertiesIsotropic, weak anomalous anisotropism
StreakWhite
Specific gravity4.2 - 6.4
DiaphaneitySubtranslucent to opaque
Other CharacteristicsVariably radioactive

Pyrochlore (Na,Ca)2Nb2O6(OH,F) is a solid solution between the niobium end member (pyrochlore), and the tatntalum 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.

Additional recommended knowledge

Pyrochlore occurs in pegmatites associated with nepheline syenites and other alkalic rocks. It also in granite pegmatites and greisens. It characteristically is 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.

See also

References

  • Webmineral - Pyrochlore
  • Mineral galleries
  • Mindat
  • Handbook of Mineralogy
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Pyrochlore". A list of authors is available in Wikipedia.
Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE