Hydropyrochlore

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Hydropyrochlore
Hydropyrochlore.jpg
Hydropyrochlore from the Lueshe Mine, Kivu , Democratic Republic of the Congo
General and classification
other names
  • Kalipyrochlore
  • "Weathered pyrochlore" (weathered pyrochlore)
chemical formula
  • (H 2 O, □) 2 Nb 2 (O, OH) 6 (H 2 O)
  • (H 2 O) (Nb, Ti) 2 (O, OH) 6 • H 2 O
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.15 ( 8th edition : IV / C.17)
02/08/01. ??
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fd 3 m (No. 227)Template: room group / 227
Lattice parameters a  = 10.570 to 10.584  Å
Formula units Z  = 8
Frequent crystal faces {111}
Physical Properties
Mohs hardness 4 to 4.5; VHN = 315–366 kg / mm² (mean value 351 kg / mm²)
Density (g / cm 3 ) 3.40 to 3.48 (measured); 3.48 to 3.42 (calculated)
Cleavage not given
Break ; Tenacity uneven; brittle
colour greenish, greenish white to greenish gray
Line color not given, probably white to very light green
transparency transparent
shine Glass to resin gloss
Crystal optics
Refractive index n  = 1.950 to 1.985
Optical character isotropic

Hydropyrochlore is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition (H 2 O, □) 2 Nb 2 (O, OH) 6 (H 2 O), i.e. it is a water-containing niobate , with H 2 O on both the A and the Y Position dominates.

Hydropyrochlore occurs at its type locality in the form of idiomorphic crystals with a maximum size of 1 cm, which show the octahedron as the supporting crystal form.

The type locality of the hydropyrochloride is the "Lueshe Mine" ( coordinates of the "Lueshe Mine" deposit ) in the Cancrinite - Syenite / Carbonatite complex of the same name , North Kivu Province , Democratic Republic of the Congo (formerly Zaire).

Etymology and history

As early as 1965, Leopold van Wambeke described a “weathered pyrochlore” from the “Lueshe Mine” in what was then Zaire . The mineral was not submitted to the International Mineralogical Association (IMA). In the first definition of the nomenclature of the pyrochlore group, this mineral was renamed Kalipyrochlore by Donald David Hogarth and colleagues in 1977 , whereupon Leopold van Wambeke published the first description of the potassium pyrochloride in 1978 . The name Kalipyrochlore was chosen because of its belonging to the pyrochlore group and the dominance of potassium over all other cations.

The type of material for Kalipyrochlor is in the collection of the catalog number 136440 Smithsonian Institution belonging to National Museum of Natural History , Washington, DC kept. The holotype stage is in the private collection of Leopold van Wambeke.

In 2010, the IMA presented a new nomenclature for the minerals of the newly defined pyrochlore upper group (pyrochlore supergroup). In it, potassium pyrochlore was redefined to hydropyrochlore ( English hydropyrochlore ), whereby the type material of potassium pyrochlore defined by L. van Wambeke is now considered the type material (including the holotype) for hydropyrochlore. The name Kalipyrochlore has been discredited. In accordance with the nomenclature of the pyrochlore upper group, the choice of the new name Hydropyrochlor occurred due to the chemical composition of the mineral with a through H 2 -dominated O A position, by Nb dominated B position, as well as H 2 -dominated O Y position. Potassium is one of the very large monovalent cations (K, Cs, Rb) that sit on the Y position, but its content in the hydropyrochlore is much lower than that of H 2 O. Since H 2 O is present on both the A - As well as dominating on the Y position, the mineral should actually be called hydrohydropyrochlore, but the nomenclature of the pyrochlore upper group requires the use of only one prefix if the first and second prefix are identical. For this reason, the mineral is not called "hydrohydropyrochlore" but "hydropyrochlore".

Pyrochlore was originally found by Nils Otto Tank (1800–1864) near Stavern in the Norwegian province of Vestfold and described in 1826 by Friedrich Wöhler . Wöhler named the mineral based on a suggestion by Jöns Jakob Berzelius after the Greek words πῦς [ pyr ] and χλωρός [ chlorós ] for "fire" and "green" because of its property, after melting with phosphorus salt (sodium ammonium hydrogen phosphate) before Solder tube to solidify to a grass-green glass. Over the decades, the term pyrochlore has often been used unspecifically and often without the background of chemical analysis. The mineral pyrochlore was discredited in 2010.

classification

The current classification of the International Mineralogical Association (IMA) counts the potassium pyrochlore (today's hydropyrochlore) to the pyrochlore upper group with the general formula A 2– m B 2 X 6– w Y 1– n , in which A , B , X and Y different positions in the structure of the minerals of the pyrochlore upper group with A  = Na, Ca, Sr, Pb 2+ , Sn 2+ , Sb 3+ , Y, U, □, or H 2 O; B = Ta, Nb, Ti, Sb 5+ or W; X = O, OH or F and Y = OH - , F, O, □, H 2 O or very large (>> 1.0 Å) monovalent cations such as K, Cs or Rb. To pyrochlore supergroup include not only Hydropyrochlor still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydroxycalciomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Hydropyrochlor forms together with Cesiokenopyrochlor, Fluorcalciopyrochlor, Fluornatropyrochl, Hydrokenopyrochl, Hydroxycalciopyrochlor, Hydroxykenopyrochl, Hydroxymanganopyrochlor, Hydroxynatropyrochl and Oxycalciopyrochlor within the pyrochlore upper group the pyrochlore group .

In the meanwhile outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the potassium pyrochlore, which was redefined as hydropyrochlore in 2010, belonged to the mineral class of "oxides and hydroxides" and there to the general section of "oxides with a metal: oxygen ratio = 2: 3 ( M 2 O 3 and related compounds) ”, where it together with bariopyrochlor (discredited 2010, possibly“ zero-valent dominant pyrochlore ”), bismuthopyrochlore (discredited 2010, possibly“ oxynatropyrochlore ”), calciobetafit (discredited 2010), ceriopyrochlor- ( Ce) (discredited 2010, possibly "Fluorkenopyrochlor"), Plumbopyrochlor (discredited 2010, possibly "Oxyplumbopyrochlor" or "Kenoplumbopyrochlor"), Pyrochlore (discredited 2010, since then group and main group name; this includes the possibly new species "Oxynatropyrochlor", "Hydroxycalciopyrochlor", "Fluorcalciopyrochlor" and "Fluorkenopyrochlor"), Uranpyrochlor (discredited 2010, poss Usually “Oxynatropyrochlore”), Strontiopyrochlore (discredited 2010, possibly “Fluorstrontiopyrochlore” or “Fluorkenopyrochlore”) and Yttropyrochlor- (Y) (discredited 2010, possibly “Oxyttropyrochlore- (Y)”) with the “Pyrochlore Group, Pyrochlore Subgroup” the system no. IV / C.17 formed.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns potassium pyrochlore (today's hydropyrochlore) to the division of "oxides with the molar ratio of metal: oxygen = 1: 2 and comparable" a. However, this section is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “With large (± medium-sized) cations; Layers of edge-linked octahedra ”can be found, where together with all representatives of the pyrochlore, microlith, Betafit, Roméit and Elsmoreit groups, the pyrochlore supergroup with the system no. 4.DH.15 forms. Hydropyrochlor is together with Fluorcalciopyrochlor , Fluornatropyrochlor , Fluorkenopyrochlor , Fluorstrontiopyrochlor , Hydroxycalciopyrochlor , Kenoplumbopyrochlor , Oxycalciopyrochlor (formerly Stibiobetafit ) Oxynatropyrochlor , Oxyplumbopyrochlor and Oxyyttropyrochlor- (Y) to be found in the Pyrochlorgruppe.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns hydropyrochlore (formerly potassium pyrochlore ) to the class of "oxides and hydroxides", but there in the category of "multiple oxides with Nb, Ta and Ti". Here it is together with pyrochlore , bariopyrochlore , yttropyrochlore (Y) , ceriopyrochlore (Ce) , plumbopyrochlore , uranium pyrochlore , strontiopyrochlore and bismuthopyrochlore (all discredited since 2010, see under Systematics of minerals according to Strunz, 8th edition) in the " Pyrochlore subgroup; Nb> Ta; (Nb + Ta)> 2 (Ti) “with the system no. 08.02.01 to be found within the subsection of " Multiple oxides with Nb, Ta and Ti with the formula A 2 (B 2 O 6 ) (O, OH, F) ".

Chemism

A microprobe analysis gave values ​​of 2.12% K 2 O; 0.12% CaO; 1.75% SrO; 65.69% Nb 2 O 5 ; 5.01% TiO 2 and 16.05% H 2 O (calculated from the crystal structure analysis). On the basis of two cations per formula unit in the B position, the empirical formula [(H 2 O) 0.99 Sr 0.05 Ca 0.01 ] Σ = 1.05 (Nb 1.80 Ti 0.20 ) Σ = 2.00 [O 4.06 (OH) 1.94 ] Σ = 6.00 [(H 2 O) 0.86 K 0.14 ] Σ = 1.00 , which leads to Nb 2 (O , OH) 6 · p H 2 O (with p  ≤ 1.75). The official notation of the IMA for the formula of hydropyrochloride is (H 2 O, ◻) 2 Nb 2 (O, OH) 6 (H 2 O).

Chemically similar to hydropyrochlore are hydrokenopyrochlore, □ 2 Nb 2 O 4 (OH) 2 (H 2 O); the “zero-valent dominant representatives of the pyrochlore group” with the general formula A 2 Nb 2 (O, OH) 6 Z ; and "UM1967-06-O: HNb", Nb 2 O 5 · 5H 2 O - a questionable alteration product of fergusonite in quartz - fluorite -Pegmatiten in the Hunger Steppe (Betpak-Dala), Karazhal, Province Karaganda , Kazakhstan .

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Hydropyrochlore is the H 2 O-dominant analogue of the vacancy-dominated hydrokenopyrochlore and of the "fluorohydropyrochlore" not yet described as a mineral, but also known from the "Lueshe Mine". Across all subgroups, hydropyrochlore is the Nb-dominant analogue of the Ta-dominated one, also not yet described as “hydromicrolite” as a mineral.

Crystal structure

Hydropyrochlore crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.570 - 10.584  Å and eight formula units per unit cell . R. Scott Ercit and colleagues determined a lattice parameter a = 10.604 Å on another crystal from the “Lueshe Mine”, which is also given by Hugo Strunz and Ernest Nickel. Template: room group / 227

The crystal structure of the Hydropyrochlors consists of a skeleton of B O 6 - octahedra with shared corners. The cations on the A position are extremely deficient (vacancies, □), so that the dominant constituents on the A position are water molecules H 2 O. At the X position, which normally only contains oxygen atoms in the representatives of the pyrochlore upper group , there are also (OH) groups, and the Y position also mainly contains H 2 O.

Hydropyrochlore is isotypic (isostructural) to all other representatives of the pyrochlore upper group that crystallize in space group Fd 3 m (space group no. 227) . Template: room group / 227

properties

morphology

Hydropyrochlore occurs at its type locality mostly in the form of idiomorphic, occasionally corroded crystals with a maximum size of 1 cm, which show the octahedron as the supporting form. Without exception, hydropyrochlore represents pseudomorphoses based on a primary precursor mineral from the pyrochlore upper group, whose formula is given by Frances Wall and colleagues as (Ca, Na) 2 Nb 2 O 6 (OH, F), i.e. corresponds to a hydroxycalciopyrochlore.

physical and chemical properties

The crystals of hydropyrochloride are greenish, greenish-white or greenish-gray at the type locality. There is no information about their line color - it should be gray-white to very light green. The surfaces of the transparent hydrochloride show a glass-like to resinous gloss , which is in good agreement with the high value for light refraction (n = 1.950 to 1.985). Hydropyrochlore is optically isotropic.

There is no information on cleavage and divisibility. Due to its brittleness , hydropyrochlore breaks like amblygonite , with the fracture surfaces being uneven. With a Mohs hardness of 4 to 4.5, the mineral is one of the medium-hard minerals, corresponds to the reference mineral fluorite (hardness 4) or lies between this and apatite (hardness 5) and can therefore be more or less easily scratched with a pocket knife. Its Vickers hardness VHS was determined to be 315-366 kg / mm² (mean value 351 kg / mm²). The measured density for hydropyrochlore is 3.40 to 3.48 g / cm³, the calculated density is 3.48 to 3.42 g / cm³.

Information on fluorescence in UV light or on cathodoluminescence under the electron beam for the mineral is missing, as is information on chemical behavior.

Education and Locations

The type locality for hydropyrochlore is the "Lueshe Mine" 150 km north of Goma in the Cancrinite - Syenite / Carbonatite complex of the same name , North Kivu Province , Democratic Republic of the Congo (formerly Zaire). The carbonatite is located in the Rwindibergen, about 70 km north of Lake Kivu and 40 km southwest of Eduard lake . This alluvial deposit (residual soils ) is a lateritically weathered Niberz, which comes from a calcite carbonatite intruded into a cancrinite syenite.

Hydropyrochlore was formed during the weathering of the carbonatite under tropical conditions. It was created by the action of potassium-rich solutions on a mineral (hydroxycalciopyrochlore?) Which also belongs to the pyrochlore upper group, which led to the removal of calcium , sodium and fluorine and an accumulation of potassium , strontium , barium and water.

Among the accompanying minerals of Hydropyrochlors include Na-Ca-rich representatives of Pyrochlorgruppe, Lueshit , Columbite- (Fe) , Fersmit , ilmenite , rutile , pseudorutile , barite , barium- Goyazit , goethite , jarosite and clay minerals .

As a very rare mineral formation, hydropyrochlore could so far (as of 2018) only be described by its type locality. Find places for hydropyrochlore in Germany , Austria and Switzerland are therefore unknown.

use

Hydropyrochlore would be a rich niobium ore due to its Nb 2 O 5 content of approx. 75% by weight. Due to its rarity, however, the mineral is of no practical importance and only of interest to mineral collectors.

See also

literature

  • Leopold van Wambeke: A study of some niobium-bearing minerals of the Lueshe carbonatite deposit (Kivu, Republic of Congo) . In: Euratom Report . tape 2110 , 1965, pp. 5-15 (English).
  • Leopold van Wambeke: Potash pyrochlore, a new mineral of the pyrochlore group . In: The American Mineralogist . tape 63 , 1978, pp. 528-530 (English, rruff.info [PDF; 254 kB ; accessed on September 16, 2019]).

Web links

Commons : Pyrochlore  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f Daniel Atencio, Marcelo B. Andrade, Andrew G. Christy, Reto Gieré, Pavel M. Kartashov: The Pyrochlore supergroup of minerals: Nomenclature . In: The Canadian Mineralogist . tape 48 , 2010, p. 673–698 , doi : 10.3749 / canmin.48.3.673 (English, rruff.info [PDF; 1,4 MB ; accessed on September 16, 2019]).
  2. ↑ a b c d e f g h i j Kalipyrochlore . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 72  kB ; accessed on October 1, 2018]).
  3. ↑ a b c d e f g h i j Leopold van Wambeke: A study of some niobium-bearing minerals of the Lueshe carbonatite deposit (Kivu, Republic of Congo) . In: Euratom Report . tape 2110 , 1965, pp. 5-15 (English).
  4. ↑ a b c d e f g Leopold van Wambeke: Kalipyrochlore, a new mineral of the pyrochlore group . In: The American Mineralogist . tape 63 , 1978, pp. 528-530 (English, rruff.info [PDF; 254 kB ; accessed on September 16, 2019]).
  5. ^ A b Adriaan Hendrik van der Veen: A study of pyrochlore . In: Verhandelingen van het Koninklijk Nederlands Geologische Mijnbouwkundig Genootschap. Geological series . tape 22 , 1963, pp. 1–188 (English, abstract in: American Mineralogist (PDF; 608 kB), 1963, 48, p. 1413).
  6. ^ Donald David Hogarth: Classification and nomenclature of the pyrochlore group . In: The American Mineralogist . tape 62 , 1977, pp. 403–410 (English, rruff.info [PDF; 869 kB ; accessed on September 16, 2019]).
  7. ↑ a b Catalog of Type Mineral Specimens - K. (PDF 96 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed on September 16, 2019 (Kalipyrochlor see p. 2).
  8. ^ A b c Andrew G. Christy, Daniel Atencio: Clarification of status of species in the pyrochlore supergroup . In: Mineralogical Magazine . tape 77 , no. 1 , 2013, p. 13–20 , doi : 10.1180 / minmag.2013.077.1.02 (English, cnmnc.main.jp [PDF; 80 kB ; accessed on September 16, 2019]).
  9. ↑ a b Friedrich Wöhler: About the pyrochlore, a new mineral species . In: Poggendorff's annals of physics and chemistry . tape 7 , no. 4 , 1826, pp. 417-428 ( limited preview in Google Book search).
  10. ^ A b c d T. Scott Ercit, Frank C. Hawthorne, Petr Černý: The structural chemistry of Kalipyrochlore, a "Hydropyrochlore" . In: The Canadian Mineralogist . tape 32 , 1994, pp. 415–420 (English, rruff.info [PDF; 562 kB ; accessed on September 16, 2019]).
  11. ↑ Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: September 2019. (PDF 2672 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, September 2019, accessed September 16, 2019 .
  12. ↑ a b Hydropyrochlore. In: mindat.org. Hudson Institute of Mineralogy, accessed September 16, 2019 .
  13. ↑ Cristian Biagioni, Nicolas Meisser, Fabrizio Nestola, Marco Pasero, Martin Robyr, Philippe Roth, Cédric Schnyder, Reto Gieré: Hydrokenopyrochlore, ( □, #) 2 Nb 2 O 6 · H 2 O, a new species of the pyrochlore supergroup from the Sahatany Pegmatite Field, Antananarivo Province, Madagascar . In: European Journal of Mineralogy . tape 30 , no. 4 , 2018, p. 869–876 , doi : 10.1127 / ejm / 2018 / 0030-2761 (English).
  14. ↑ Mohamed Nasraoui, Essaid Bilal: Pyrochlores from the Lueshe carbonatite complex (Democratic Republic of Congo): a geochemical record of different alteration stages . In: Journal of Asian Earth Sciences . tape 18 , no. 2 , 2000, pp. 237-251 , doi : 10.1016 / S1367-9120 (99) 00056-5 (English, researchgate.net [PDF; 1.9 MB ; accessed on October 1, 2018]).
  15. ^ 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.  222–223 (as potassium pyrochlore; ignore the misleading assignment hydropyrochlore = pyrochlore on p. 787).
  16. ↑ a b c d Frances Wall, C. Terry Williams, Alan Woolley, Mohamed Nasraoui: Pyrochlore from weathered carbonatite at Lueshe, Zaire . In: Mineralogical Magazine . tape 60 , no. 5 , 1996, pp. 731–750 , doi : 10.1180 / minmag.1996.060.402.03 (English).
  17. ↑ Mindat - Number of locations for hydropyrochlore , accessed on October 1, 2018 (English)
  18. ↑ List of locations for hydropyrochlore in the Mineralienatlas and Mindat (accessed on September 16, 2019)