Oxycalciopyrochlor

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Oxycalciopyrochlor
Oxycalciopyrochlore.jpg
Orange-colored, sharp-edged octahedral oxycalciopyrochlore crystal from Schelingen, Kaiserstuhl, Baden-Württemberg, Germany
General and classification
other names

Stibiobetaite

chemical formula
  • Ca 2 Nb 2 O 6 O
  • (Ca, Sb 3+ ) 2 (Ti, Nb, Ta) 2 (O, OH) 7
  • (Sb 3+ , Ca) 2 (Ti, Nb, Ta) 2 (O, OH) 7
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.15 ( 8th edition : IV / C.16)
02/08/03/04
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  = 10.356 (natural); 10.351 (heated to 700 ° C)  Å
Formula units Z  = 8
Frequent crystal faces {111}, {100}
Physical Properties
Mohs hardness ≈ 5
Density (g / cm 3 ) 5.30 (measured); 5.19 (calculated)
Cleavage not given
Break ; Tenacity shell-like to uneven; brittle
colour brownish black, dark brown, black brown; Various shades of brown in transmitted light, gray in incident light
Line color pale brownish to creamy white
transparency semi-transparent
shine Glass gloss
Crystal optics
Refractive index n  > 1.78 (measured); 2.2 (calculated)
Optical character isotropic

Oxycalciopyrochlor , formerly stibiobetafite , is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition of Ca 2 Nb 2 O 6 O, is thus a calcium - niobate with additional oxygen ions .

Oxycalciopyrochlor occurs at its type locality mainly as a xenomorphic displacement in dikes and aggregates of columbite and niobium-containing rutile. Adhesions of columbite, niobium-containing rutile, cassiterite and zircon, penetrated and covered by stibiobetaite and stokesite, are rarely found in albite-lined miarolithic cavities. More rarely, oxycalciopyrochlore also forms poorly developed crystals with a maximum size of 8 mm in open cavities , which show the octahedron as a supporting crystal form with corner-truncating surfaces of the hexahedron .

The type locality of the Oxycalciopyrochlors is the "Pegmatit Věžná I" ( coordinates of the "Pegmatite Věžná I" ) near Věžná , Okres Pelhřimov , District Žďár nad Sázavou , Highlands Region , Czech Republic .

Etymology and history

In 1961 Petr Černý found a mineral in pegmatites around Věžná, which was provisionally described as antimony-containing pyrochlore. Only at the end of the 1970s did quantitative microanalytical investigations lead to the realization that this phase was a new mineral. The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 1978 under the temporary designation IMA 1978-052 . The first scientific description of this mineral was made in 1979 by a Canadian-American research team with Petr Černý , Frank C. Hawthorne , Joseph Hector Gilles Laflamme and James Hinthorne in the Canadian science magazine The Canadian Mineralogist . The authors named the new mineral in accordance with the nomenclature of the then pyrochlore group after Donald David Hogarth and colleagues due to its chemical composition with antimony ( Latin stibium ) as the dominant cation on the A position and the proportions on the B position [with 2Ti> (Nb + Ta) and thus representatives of the Betafit subgroup of the pyrochlore group] as Stibiobetafite ( English Stibiobetafite ).

The type material for stibiobetafite is stored under catalog number M5233 in the collection of the Mineralogical Museum of the Department of Geological Sciences , University of Manitoba , Canada , and in the collection of the Royal Ontario Museum , Toronto , Canada (polished section, catalog number M35630).

In 2010, the IMA presented a new nomenclature for the minerals of the newly defined pyrochlore upper group (pyrochlore supergroup). In it, stibiobetafit was redefined to oxycalciopyrochlor ( English Oxycalciopyrochlore ), whereby the type material of stibiobetafit defined by Petr Černý and colleagues is now the type material (including the holotype) for oxycalciopyrochlor. The name stibiobetafit has been discredited. In accordance with the nomenclature of the pyrochlore upper group, the choice of the new name Oxycalciopyrochlor was based on the chemical composition of the mineral with an A position dominated by calcium , B position dominated by Nb and Y position dominated by O.

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 stibiobetafite (today's oxycalciopyrochlor) 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 Oxycalciopyrochlor still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydroxycalciomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Oxycalciopyrochlor, together with cesiokenopyrochlor, fluorcalciopyrochlor, fluoronatropyrochlore, hydrokenopyrochlor, hydropyrochlore, hydroxycalciopyrochlor, hydroxykenopyrochlor, hydroxymanganopyrochlor and hydroxynatropyrochlor within the pyrochlore upper group, forms the pyrochlore group .

In the 8th edition of the mineral systematics according to Strunz , which is now outdated, but in some cases still in use , the stibiobetafite, which was redefined in 2010 to oxycalciopyrochlor, 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 Betafit (discredited 2010, possibly Oxycalciobetafit or Oxyuranobetafit ), Plumbobetafit (discredited 2010, zero-valent dominant pyrochlore) and Yttrobetafit- (Y) (discredited 2010, zero-valent -dominant pyrochlore; yttrobetafit- (Y) from the moon is oxycalciobetafit ) the "pyrochlore group, betafit subgroup" with the system no. IV / C.16 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), classifies oxycalciopyrochlor (formerly stibiobetafit ) in the department of "oxides with the molar ratio metal: oxygen = 1: 2 and comparable" . 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. Oxycalciopyrochlor is together with Fluorcalciopyrochlor , Fluornatropyrochlor , Fluorkenopyrochlor , Fluorstrontiopyrochlor , Hydropyrochlor (formerly Kalipyrochlor ) Hydroxycalciopyrochlor , Kenoplumbopyrochlor , 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 stibiobetafite (today oxycalciopyrochloride) 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 Betafit , Yttrobetafit- (Y) , Plumbobetafit and Calciobetafit (all discredited since 2010, see under Systematics of Minerals according to Strunz, 8th edition) in the “Betafit subgroup; 2 (Ti)> (Ta + Nb) “with the system no. 02/08/03 within the subsection of " Multiple oxides with Nb, Ta and Ti with the formula A 2 (B 2 O 6 ) (O, OH, F) ".

Chemism

Analyzes with electron beams ( microprobe ) and ion beams ( secondary ion microprobe ) on various stibiobetaite grains of the type locality yielded mean values ​​of 21.6% Nb 2 O 5 ; 19.3% Ta 2 O 5 ; 16.5% TiO 2 ; 0.49% Al 2 O 3 ; 23.2% Sb 2 O 3 ; 0.13% PbO; 2.9% SnO; 0.6% FeO; 0.6% MnO; 14.5% CaO; 0.30% Na 2 O; 0.15% F 2 , 0.44% H 2 O and [(-O ≡ F 2 ) -0.06%, sum = 100.65%]. Based on seven anions (O, OH, F) per formula unit, the empirical formula (Ca 1.11 Sb 3+ 0.69 Sn 2+ 0.09 Fe 0.04 Mn 0.04 Na 0.04 ) Σ = 2.01 (Ti 4+ 0.89 Nb 5+ 0.70 Ta 5+ 0.38 Al 3+ 0.04 ) Σ = 2.01 O 6 [O 0.76 (OH) 0.21 F 0.03 ] Σ = 1.00 , which can be simplified to (Ca, Sb 3+ ) 2 (Ti, Nb, Ta) 2 (O, OH) 7 . The official notation of the IMA for the formula of oxycalciopyrochloride is Ca 2 Nb 2 O 6 O.

Oxycalciopyrochlor from "Atagoyama", Japan , contains between 23.94% and 25.12% UO 2 . Some samples of the beta-fit in the sense of Hogarth (1977) have been found to be titanium - uranium- containing oxycalciopyrochlore with contents of 24.7% by weight UO 2 and 3.2% by weight ThO 2 .

Oxycalciopyrochlor is the only mineral with the element combination "Ca - Nb - O". Chemically similar to Oxycalciopyrochlor are a number of minerals, including z. B. Calciosamarskite , (Ca, Fe 3+ , Y) 2 (Nb, Ta, Ti) 2 O 8 ; Charleshatchettite , CaNb 4 O 10 (OH) 2 • 8H 2 O; and Fersmit , (Ca, Ce, Na) (Nb, Ta, Ti) 2 (O, OH, F) 6 .

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Oxycalciopyrochlor is the O-dominant analog of the F-dominated fluorocalciopyrochloride and the OH-dominated hydroxycalciopyrochloride. Across all subgroups, oxycalciopyrochlor is the Nb-dominant analogue of the Sb-dominated oxycalcioroméite.

Crystal structure

Oxycalciopyrochlor crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.356  Å and eight formula units per unit cell . Template: room group / 227

As consisting of all representatives of the pyrochlore upper group crystal structure of Oxycalciopyrochlors from B O 6 - octahedra - in this case (Nb, Ta, Ti) O 6 octahedra - with shared corners, the layers of three and six-membered rings parallel [110] form. In these layers there are channels in the direction 110, which take up the atoms such as Ca (and Sb 3+ , Sn 2+ , Fe, Mn and Na) sitting on the A position .

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

properties

Drawing of a cuboctahedral oxycalciopyrochlore crystal

morphology

Oxycalciopyrochlor ( stibiobetafite ) occurs at its type locality mainly as a xenomorphic displacement in ducts and aggregates of columbite and niobium-containing rutile. Adhesions of columbite, niobium-containing rutile, cassiterite and zircon, penetrated and covered by stibiobetaite and stokesite, are rarely found in albite-lined miarolithic cavities. Oxycalciopyrochlor also rarely forms poorly developed crystals with a maximum size of 8 mm in open cavities with the octahedron {111} as the supporting crystal form, which show the corner-blunting surfaces of the cube {100} (see the crystal drawing on the right).

physical and chemical properties

The crystals of oxycalciopyrochloride ( stibiobetafite ) are brownish-black, dark brown or black-brown at the type locality, their line color is indicated as pale brownish to creamy white. After heating the oxycalciopyrochloride for one hour at 700 ° C, the color changes to pale orange. In light transmitted through thin sections , the mineral shows various shades of brown, in reflected light it is medium gray and significantly darker than columbite and niobium-containing rutile. The surfaces of the semitransparent oxycalciopyrochloride show a glass-like gloss , which agrees well with the high value for the refraction of light (n> 1.78 (measured) or n = 2.2 (calculated)). Oxycalciopyrochlor is optically isotropic.

There is no information on cleavage and divisibility for oxycalciopyrochlor. Due to its brittleness , hydropyrochlore breaks in a similar way to quartz or amblygonite , whereby the break surfaces are scalloped to uneven. With a Mohs hardness of ≈ 5, the mineral is one of the medium-hard minerals which, like the reference mineral apatite (hardness 5), can still be scratched with a pocket knife. The measured density for oxycalciopyrochlore is 5.30 g / cm³, the calculated density is 5.19 g / cm³.

There is no information on fluorescence in UV light or on cathodoluminescence under the electron beam for the mineral, as well as information on chemical behavior.

Education and Locations

The type locality for Oxycalciopyrochlor is the "Pegmatit Věžná I" near Věžná on the northeastern edge of the Bohemian Massif , Okres Pelhřimov , District Ž Distrár nad Sázavou , Highlands Region , Czech Republic . The pegmatite consists mainly of sodium-rich plagioclase and quartz, occasionally in graphical intergrowth , and is separated from the ultra-basic host rock by a banded reaction rim made of anthophyllite , talc , tremolite and altered phlogopite .

The accompanying minerals of oxycalciopyrochloride include columbite , niobium-containing rutile, solid antimony , stokesite , cassiterite , zircon and albite .

From the point of view of the geochemistry of the pegmatite type locality, the occurrence of oxycalciopyrochlore ( stibiobetafite ) is anomalous. The host rock and the genetically related pegmatites in the vicinity are characterized by mineralization with Ti, Nb> Ta, Be, Zr, B, Sn and REE, which is normally free of mineralogically conspicuous quantities of antimony. On the other hand, antimony is mostly found in lithium - rubidium - cesium- rich pegmatites, which are also characterized by substantial mineralization of B, Be, Ta> Nb and Sn with negligible, if any, contents of Ti and REE. All characteristics of the behavior of antimony in granite pegmatites, namely the preference for types with enrichment of rare alkali metals, characteristic minerals and the "avoidance" of the structure of pyrochloride liberals of the microlith group support the argument that the occurrence of oxycalciopyrochlore ( stibiobetafite ) at its type locality is coincidental and the mineral is most likely not found in other pegmatites.

As a very rare mineral formation, the Oxycalciopyrochlor could so far (as of 2018) only be described from around ten sites worldwide.

In addition to the type locality, the following sites are known for Oxycalciopyrochlor:

Locations for Oxycalciopyrochlor in Austria and Switzerland are therefore unknown.

use

Oxycalciopyrochlor would be a rich niobium / tantalum ore due to its Nb 2 O 5 content of 20.1 to 26.3% by weight and Ta 2 O 5 content of 9.0 to 20.0% by weight. Due to its rarity, however, the mineral is of no practical importance and only of interest to mineral collectors.

See also

literature

  • Petr Černý, Frank C. Hawthorne, Joseph Hector Gilles Laflamme, James Hinthorne: Stibiobetafite, a new member of the Pyrochlore Group from Vezná, Czechoslovakia . In: The Canadian Mineralogist . tape 17 , 1979, pp. 583-588 (English, rruff.info [PDF; 751 kB ; accessed on October 3, 2018]).
  • Stibiobetafite . 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; 70 kB ; accessed on October 1, 2018]).

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB)
  2. ↑ a b c d e f g Stibiobetafite . 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; 70  kB ; accessed on October 1, 2018]).
  3. ↑ Mineralienatlas - Oxycalciopyrochlor , accessed on October 3, 2018
  4. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z Petr Černý, Frank C. Hawthorne, Joseph Hector Gilles Laflamme, James Hinthorne: Stibiobetafite, a new member of the Pyrochlore Group from Vezná, Czechoslovakia . In: The Canadian Mineralogist . tape 17 , 1979, pp. 583-588 (English, rruff.info [PDF; 751 kB ; accessed on October 3, 2018]).
  5. ^ A b Donald David Hogarth: Classification and nomenclature of the pyrochlore group . In: The American Mineralogist . tape 62 , 1977, pp. 403-410 (English, rruff.info [PDF; 849 kB ; accessed on September 3, 2018]).
  6. ^ A b Petr Černý, Frank C. Hawthorne, Joseph Hector Gilles Laflamme, James Hinthorne: Stibiobetafite, a new member of the Pyrochlore group from Vezna, Czechoslovakia . In: The Canadian Mineralogist . tape 17 , 1979, pp. 583-588 (English, rruff.info [PDF; 750 kB ; accessed on September 27, 2018]).
  7. ↑ a b c d 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 August 30, 2018]).
  8. ^ A b Andrew G. Christy, Daniel Atencio: Clarification of the 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, main.jp [PDF; 85 kB ; accessed on August 30, 2018]).
  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 Satoshi Matsubara, Ritsuro Miyawaki, K. Yokoyama, Koichi Momma, Masako Shigeoka, E. Hashimoto: Pyrochlore and microlite in a pegmatite at Atagoyama, Koriyama City, Fukushima Prefecture, Japan . In: Bulletin of the National Museum of Nature and Science, Ser. C . tape 39 , 2013, p. 1–6 (English, kahaku.go.jp [PDF; 6.4 MB ; accessed on October 3, 2018]).
  11. ↑ a b c d Mindat - Oxycalciopyrochlore , accessed on October 1, 2018 (English)
  12. ↑ Li Guowu, Yang Guangming, Lu Fude, Xiong Ming, Ge Xiangkun, Pan Baoming, Jeffrey de Fourestier: Fluorcalciopyrochlor, a new mineral species from Bayan Obo, Inner Mongolia, PR China . In: The Canadian Mineralogist . tape 54 , no. 5 , 2016, p. 1285–1291 , doi : 10.3749 / canmin.1500042 (English).
  13. ↑ Yang Guangming, Li Guowu, Xiong Ming, Pan Baoming, Yan Chenjie: Hydroxycalciopyrochlore, a new mineral species from Sichuan, China . In: Acta Geologica Sinica (english edition) . tape 88 , no. 3 , 2014, p. 748-753 , doi : 10.1111 / 1755-6724.12235 (English).
  14. ↑ Cristian Biagioni, Paolo Orlandi, Fabrizio Nestola, Sara Bianchin: Oxycalcioroméite, Ca 2 Sb 2 O 6 O, from Buca della Vena mine, Apuan Alps, Tuscany, Italy: a new member of the pyrochlore supergroup . In: Mineralogical Magazine . tape 77 , 2013, p. 3027–3037 , doi : 10.1180 / minmag.2013.077.7.12 (English).
  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 .
  16. ↑ Mindat - Number of locations for Oxycalciopyrochlor , accessed on October 1, 2018 (English)
  17. ↑ a b List of locations for Oxycalciopyrochlor in the Mineralienatlas and Mindat (accessed on October 3, 2018)