Pyrochlore () is a mineral group of the

niobium Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...

end member of the pyrochlore supergroup. Pyrochlore is also a term for the crystal structure ''F''dm. The name is from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

, ''fire'', and , ''green'' because it typically turns green on ignition in classic blowpipe analysis.

Mineral

The general formula, (where A and B are metals), represent a family of phases isostructural to the mineral pyrochlore. Pyrochlores are an important class of materials in diverse technological applications such as luminescence, ionic conductivity, nuclear waste immobilization, high-temperature thermal barrier coatings, automobile

exhaust gas Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through ...

control, catalysts, solid oxide fuel cell, ionic/electrical conductors etc. The mineral is associated with the

metasomatic Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical com ...

end stages of magmatic intrusions. Pyrochlore crystals are usually well-formed (euhedral), occurring usually as octahedra of a yellowish or brownish color and

resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

ous luster. It is commonly metamict due to radiation damage from included radioactive elements. Pyrochlore occurs in

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

s associated with

nepheline syenite Nepheline syenite is a holocrystalline Intrusion, plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, but dark green varie ...

s and other alkalic rocks. It is also found in

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

pegmatites and greisens. It is characteristically found in

carbonatite Carbonatite () is a type of intrusive rock, intrusive or extrusive rock, extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geoche ...

s. Associated minerals include

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

, aegirine,

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

perovskite Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as , known as the perovskite (stru ...

and columbite.

History

It was first described in 1826 for an occurrence in Stavern (Fredriksvärn),

Larvik Larvik () is a List of municipalities of Norway, municipality in Vestfold county, Norway. It is located in the Traditional districts of Norway, traditional district of Vestfold. The administrative centre of the municipality is the Larvik (town) ...

, Vestfold, Norway.

Niobium mining

The three largest producers of niobium ore are mining pyrochlore deposits. The largest deposit in

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

is the CBMM mine located south of Araxá, Minas Gerais, followed by the deposit of the Catalão mine east of

Catalão Catalão () is a city and municipality located in the south of the state of Goiás, in Brazil. It is a large producer of grains, cattle, and phosphates and has a John Deere and Mitsubishi factory. Demographics *Population density: 17.85 inhab ...

, Goiás. The third largest deposit of niobium ore is Niobec mine west of Saint-Honoré near

Chicoutimi Chicoutimi ( , ) is the most populous borough (arrondissement) of the city of Saguenay in Quebec, Canada. It is situated at the confluence of the Saguenay and Chicoutimi rivers. During the 20th century, it became the main administrative and ...

, Quebec. Pyrochlore ore typically contains greater than 0.05% of naturally occurring radioactive

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

and

thorium Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and ha ...

. Lueshe in

North Kivu North Kivu () is a Provinces of the Democratic Republic of the Congo, province bordering Lake Kivu in the eastern Democratic Republic of the Congo. The capital city is Goma. Spanning approximately 59,483 square kilometers with a population esti ...

, Democratic Republic of Congo, has substantial deposits of pyrochlore.

Crystal structure

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 direction. The additional anion vacancy resides in the tetrahedral interstice between adjacent B-site cations. These systems are particularly susceptible to

geometrical frustration In condensed matter physics, geometrical frustration (or in short, frustration) is a phenomenon where the combination of conflicting inter-atomic forces leads to complex structures. Frustration can imply a plenitude of distinct ground states at ab ...

and novel magnetic effects. The pyrochlore structure shows varied physical properties spanning electronic

insulators Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work ...

(e.g. La₂Zr₂O₇), ionic conductors (Gd_1.9Ca_0.1Ti₂O_6.9), metallic conductors (Bi₂Ru₂O_7−''y''), mixed ionic and electronic conductors,

spin ice A spin ice is a magnetic substance that does not have a single minimal-energy state. It has magnetic moments (i.e. "spin") as elementary degrees of freedom which are subject to frustrated interactions. By their nature, these interactions preve ...

systems (Dy₂Ti₂O₇), spin glass systems (Y₂Mo₂O₇), haldane chain systems (Tl₂Ru₂O₇) and superconducting materials (Cd₂Re₂O₇). More disordered structures, such as the bismuth pyrochlores, have also been investigated due to interesting high-frequency dielectric properties. The crystal structure has been investigated for use in solid electrolytes for lithium iron batteries. It is alleged to provide high conductivity while inhibiting dendrite growth.

References

*{{cite journal, last2= Andrade, first2= M. B. , date=2022 , title=Prospection of pyrochlore and microlite mineral groups through Raman spectroscopy coupled with artificial neural networks , journal=Journal of Raman Spectroscopy , doi=10.1002/jrs.6433, last1=Queiroz, first1= A. A. A. E., volume= 53 , issue= 11 , pages= 1924–1930 , bibcode= 2022JRSp...53.1924E , s2cid= 251463725 Sodium minerals Calcium minerals Niobium minerals Radioactive gemstones Oxide minerals Cubic minerals Minerals in space group 227 Minerals described in 1826

Mineral

History

Niobium mining

Crystal structure

See also

References