Pyrochlore
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| Pyrochlore | |
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| General and classification | |
| chemical formula | Ca 2 Nb 2 O 7 |
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Mineral class (and possibly department) |
Oxides and hydroxides |
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System no. to Strunz and to Dana |
4.DH.15 ( 8th edition : IV / C.17) 02/08/01/01 |
| Similar minerals | Zirconolite , calcirtite |
| Crystallographic Data | |
| Crystal system | cubic |
| Crystal class ; symbol | cubic hexakisoctahedral; 4 / m 3 2 / m |
| Room group (no.) | Fd 3 m (No. 227) |
| Lattice parameters | a = 10.4 Å |
| Formula units | Z = 8 |
| Frequent crystal faces | {001}, {011}, {112}, {113} |
| Twinning | rarely after {111} |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | measured: 4.45 to 4.90 |
| Cleavage | indistinct after {111} |
| Break ; Tenacity | shell-like |
| colour | brown, reddish brown to black; yellowish, red (Koppit). |
| Line color | brown to yellowish brown |
| transparency | translucent to opaque |
| shine | Greasy shine |
| radioactivity | often radioactive |
| Crystal optics | |
| Refractive index | n = 1.9 to 2.2 |
Pyrochlore is a frequently occurring mineral from the mineral class of " oxides and hydroxides " with the idealized chemical composition Ca 2 Nb 2 O 7 . It crystallizes in the cubic crystal system and often forms octahedral crystals with brown, red, greenish, orange, yellowish or black color.
Special properties
Numerous other elements can be incorporated into the crystal structure through substitution . The mineral can contain a large amount of rare earths , uranium and thorium . The radioactivity of uranium and thorium can destroy the crystal lattice, "isotropic" the mineral and turn it into an amorphous metamict . However , it can be recrystallized again by heating it out.
Etymology and history
The name pyrochlore (Greek πυρ pyr = fire, χλωρός chlorós = green) goes back to the property of the mineral to solidify after melting with phosphorus salt (sodium ammonium hydrogen phosphate) before the soldering tube to a green glass.
Pyrochlore was first found in 1826 near Stavern in the Norwegian province of Vestfold and described by Friedrich Wöhler .
classification
In the now outdated system of minerals according to Strunz (8th edition) , pyrochlore still belongs to the oxides division with the molar ratio of metal: oxygen = 2: 3.
With the revision of Strunz's mineral system in the 9th edition , however, the departments were partially redefined and subdivided more precisely. The pyrochlore can therefore now be found in the subdivision of "Oxides with the molar ratio metal: oxygen = 1: 2 and comparable, with large (± medium-sized) cations and layers of edge-linked octahedra".
The systematics of minerals according to Dana , which is common in the English-speaking world , also assigns pyrochlore to the class of oxides and hydroxides, but there in the subdivision of multiple oxides with Nb, Ta and Ti; with the formula A 2 (B 2 O 6 ) (O, OH, F) . There it is the eponymous mineral of the "pyrochlore group (pyrochlore subgroup; Nb> Ta; (Nb + Ta)> 2 (Ti))".
Modifications and varieties
Numerous modifications and varieties of pyrochloride have been described due to the wide variety of substitution possibilities. Koppit is cherry-red in color and contains Ce , the black mutaraite contains large amounts of Zn and Fe , in the greenish- brown betafit , in addition to U, there are significant proportions of rare earth elements and Pb .
Education and Locations
Pyrochlore is often associated with apatite , Aegirin , zirconium and rare earth minerals associated . It mostly occurs in alkali pegmatites and in carbonatites (Koppit e.g. in Kaiserstuhl / Baden-Württemberg).
As a frequent mineral formation, pyrochlore can be found in many localities, whereby so far (as of 2013) over 2300 localities are known.
In Germany, the mineral occurred in many places in the Black Forest (Münstertal, Oberwolfach, Sulzburg) in Baden-Württemberg, in some places in the Bavarian Forest , in the Taunus (Silbergaut and Phillipseck pit) in Hesse, in several places in the Harz (Bad Lauterberg, Clausthal -Zellerfeld, St Andreasberg, Harzgerode) from Lower Saxony to Saxony-Anhalt, in the Sauerland and Siegerland in North Rhine-Westphalia, in many places in the Eifel (Laacher See, Rieden, Westerwald) and in some places in Saxony and Thuringia .
In Austria, pyrochlore has so far been found mainly in Carinthia , including in the Friesach - Hüttenberg area and the Gurktal Alps , but also in several places in Lower Austria (Bucklige Welt), Salzburg (Lungau), Styria and in the Tyrolean Inn Valley .
In Switzerland, the mineral is so far only known from the Hinterrheintal , from the Chlitobel and the Murettopass in the canton of Graubünden, from the Weisstannental in St Gallen and from Malcantone in Ticino.
Other sites are in Afghanistan, Egypt, Algeria, Angola, Argentina, Ethiopia, Australia, Bolivia, Brazil, Chile, China, the Democratic Republic of the Congo, Finland, France, French Guiana, French Polynesia, Gabon, Greece, Greenland , Guatemala, Guinea, Guyana, India, Iran, Ireland, Italy, Japan, Cameroon, Canada, Kazakhstan, Kenya, Kyrgyzstan, Luxembourg, Madagascar, Malawi, Malaysia, Mali, Morocco, Macedonia, Mexico, Mongolia, Mozambique, Myanmar, Namibia, New Zealand, Niger, Nigeria, North and South Korea, Norway, Pakistan, Paraguay, Peru, Poland, Portugal, Rwanda, Romania, Russia, Zambia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Somalia and Somaliland, Spain, South Africa , Swaziland, Tajikistan, Tanzania, Thailand, the Czech Republic, Turkey, Uganda, Ukraine, Hungary, Uzbekistan, Venezuela, the United Kingdom (Great Britain), the United States of America (USA) and Vietnam.
Pyrochlore could also be detected on the moon , more precisely in the rock samples brought by the Luna 24 probe from the Mare Crisium and the Apollo 14 mission from the Fra Mauro highlands .
Crystal structure
Pyrochlore crystallizes cubically in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.4 Å and eight formula units per unit cell .
use
Since the mineral contains a high proportion of niobium, it is of interest to the aerospace industry. Niobium alloys are considered to be wear and corrosion resistant. The mineral is also required for the production of superconductors.
See also
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 520 .
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 86 .
Web links
- Mineral Atlas: Pyrochlore (Wiki)
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names - Pyrochlore (English, PDF 1.8 MB; p. 235)
- ↑ Webmineral - Pyrochlore (English)
- ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 222 .
- ↑ a b c d Pyrochlore , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 69.6 kB )
- ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 407 .
- ↑ Mindat - Pyrochlore
- ↑ a b Mindat - Localities for Pyrochlore