Fluorcalciopyrochlor

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Fluorcalciopyrochlor
Pyrochlore-41828.jpg
Slightly distorted pyrochlore octahedron (possibly Fluorcalciopyrochlor) from the "Tatarskii massif" in the area of ​​the Tatarka Range, Yenisei Ridge , Krasnoyarsk Region , Siberian Federal District , Russia (size: 10.1 cm × 10.0 cm × 10.0 cm)
General and classification
other names

IMA 2013-055

chemical formula (Ca, Na) 2 Nb 2 O 6 F
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  = 10.4164  Å
Formula units Z  = 8
Frequent crystal faces {111}, {110}, {100},
Physical Properties
Mohs hardness 5; Vickers hardness VHS = 424 kg / mm 2
Density (g / cm 3 ) 4.34 (calculated)
Cleavage no
Break ; Tenacity clamshell; brittle
colour brownish yellow to reddish orange, brown when thinly sectioned
Line color light yellow
transparency translucent to translucent
shine Diamond shine, greasy shine on broken surfaces
Crystal optics
Refractive index n  = 2.06
Optical character isotropic
Other properties
Chemical behavior resistant to HCl or HNO 3

Fluorcalciopyrochlor is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition (Ca, Na) 2 Nb 2 O 6 F, so it is a calcium - sodium - niobate with additional fluorine ions.

Fluorcalciopyrochlor occurs at its type locality in the form of idiomorphic crystals with a maximum size of 0.3 mm, which form octahedra , rhombic dodecahedron , hexahedron or combinations of these flat shapes.

The type locality of Fluorcalciopyrochlors is the 1927 as iron deposit discovered huge polygenic REE - iron - niobium -Lagerstätte Bayan-Obo ( coordinates of the deposit Bayan-Obo ) in the Mining Division of Bayan-Obo north of the city district Bayan-Obo the prefecture-city Baotou , autonomous region inside Mongolia in the People's Republic of China .

Etymology and history

The mineral pyrochlore , which has been discredited since 2010 , was first 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 after 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.

A fluorine-rich pyrochlore was first mentioned in 1961 by Donald David Hogarth , but here - as in later work - the material was never sufficiently investigated and characterized for recognition as a new mineral. Fluorcalciopyrochlor was first mentioned as a possible new species in 2013 by Andrew Christy & Daniel Atencio .

During the processing of material from carbonatites within the Bayan-Obo deposit, Inner Mongolia in the People's Republic of China, a mineral turned out to be a new member of the pyrochlore group. After determining the corresponding properties, the new mineral was submitted to the International Mineralogical Association (IMA), which recognized it in 2016 under the provisional designation "IMA 2013-055". The first scientific description of this mineral was made in 2016 by a Chinese-Canadian research team with Li Guowu, Yang Guangming, Lu Fude, Xiong Ming, Ge Xiangkun, Pan Baoming and Jeffrey de Fourestier in the Canadian science magazine The Canadian Mineralogist .

The authors named the new mineral in accordance with the nomenclature of the pyrochlore upper group due to its chemical composition with an A position dominated by calcium , a B position dominated by niobium and a Y position dominated by fluorine as Fluorcalciopyrochlor ( English Fluorcalciopyrochlore ).

The type material for Fluorcalciopyrochlore is kept under catalog number M12182 (holotype) in the collection of the Chinese Geological Museum in Beijing , China.

classification

The current classification of the International Mineralogical Association (IMA) counts the Fluorcalciopyrochl 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 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 Fluorcalciopyrochlor still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydroxycalciomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Fluorcalciopyrochlor, together with cesiokenopyrochlor, fluoronatropyrochlore, hydrokenopyrochlore, hydropyrochlore, hydroxycalciopyrochlor, hydroxykenopyrochlor, hydroxymanganopyrochlor, hydroxynatropyrochlore and oxycalciopyrochlor within the pyrochlore upper group, forms the pyrochlore group .

The 8th edition of the mineral systematics according to Strunz , which is now outdated, but still in use in some cases, does not yet list fluoroccalciopyrochloride. It would belong to the mineral class of "oxides and hydroxides" and there to the general division of "oxides with a metal: oxygen ratio = 2: 3 (M 2 O 3 and related compounds)", where together with bariopyrochlore (discredited 2010, possibly " Zero-valent-dominant pyrochlore "), bismuthopyrochlore (discredited 2010, possibly" Oxynatropyrochlore "), Calciobetafit (discredited 2010), Ceriopyrochlor- (Ce) (discredited 2010, possibly" Fluorkenopyrochlore "), Kalipyrochlore (2010 redefined to hydropyrochlore), Plumbopyrochlor (discredited 2010, possibly "Oxyplumbopyrochlor" or "Kenoplumbopyrochlor"), Pyrochlore (discredited 2010, since then group and parent group name; this includes the possibly new species "Oxynatropyrochlor", "Hydroxycalciopyrochlor", "Fluorcalciopyrochlor" and "Fluorkenopyrochlor"), Uranpyrochlor (discredited 2010, possibly “Oxynatropyrochlor”), Strontiopyrochlor (discredited 2010, possibly “Fluorstrontiopyroc hlor "or" Fluorkenopyrochlor ") and Yttropyrochlor- (Y) (discredited 2010, possibly" Oxyyttropyrochlor- (Y) ") the" Pyrochlore Group, Pyrochlore Subgroup "with the system no. IV / C.17 would have 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 the Fluorcalciopyrochlor 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. Fluorcalciopyrochlor is together with Fluornatropyrochlor , Fluorkenopyrochlor , Fluorstrontiopyrochlor , Hydropyrochlor (formerly Kalipyrochlor ) Hydroxycalciopyrochlor , Kenoplumbopyrochlor , Oxycalciopyrochlor (formerly Stibiobetafit ) Oxynatropyrochlor , Oxyplumbopyrochlor , Oxyyttropyrochlor- (Y) to be found in the Pyrochlorgruppe.

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking area , does not yet know the Fluorcalciopyrochlor. It would be classified in the class of "oxides and hydroxides", but there in the department of "multiple oxides with Nb, Ta and Ti". Here he was, along with pyrochlore , Kalipyrochlor , Bariopyrochlor , Yttropyrochlor- (Y) , Ceriopyrochlor- (Ce) , Plumbopyrochlor , Uranpyrochlor , Strontiopyrochlor and Bismutopyrochlor (all since 2010 discredited. See under classification of minerals by Strunz 8th edition) 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

Ten microprobe analyzes on five individual grains yielded mean values ​​of 6.30% Na 2 O; 17.59% CaO; 0.10% FeO; 0.85% SrO; 0.24% PbO; 2.51% Ce 2 O 3 ; 0.50% La 2 O 3 ; 0.57% Nd 2 O 3 ; 0.42% Y 2 O 3 ; 6.31% TiO 2 ; 0.26% UO 2 ; 61.36% Nb 2 O 5 ; 4.76% F; 0.76% ThO 2 ; 0.51% ZrO 2 ; 0.30% SnO 2 and [(2F ≡ O) -2.00%, sum = 101.4%]. Possible contents of Ta 2 O 5 and MnO were below the detection limit. On the basis of seven anions per formula unit, the empirical formula (Ca 1.14 Na 0.74 Ce 0.06 Sr 0.03 Th 0.01 Fe 0.01 Y 0.01 La 0.01 Nd 0.01 ) Σ = 2.02 (Nb 1.68 Ti 0.29 Zr 0.02 Sn 0.01 ) Σ = 2.00 O 6.00 (F 0.92 O 0.08 ) 1.00 calculated that to (Ca, Na) 2 Nb 2 O 6 F has been simplified.

Of all minerals only fluorocalyopyrochlore contains the element combination Ca - Nb - O - F. In addition, eveslogite , (Na, K, Ca, Sr, Ba) 48 [(Ti, Nb, Mn, Fe 2+ ) 12 Si 48 O 144 have (OH) 12 ] (F, OH, Cl) 14 , Fersmanite , Ca 4 (Na, Ca) 4 (Ti, Nb) 4 (Si2O 7 ) 2 O 8 F 3 , Fersmit , (Ca, Ce, Na) ( Nb, Ta, Ti) 2 (O, OH, F) 6 , Haineaultite , (Na, Ca) 5 Ca (Ti, Nb) 5 (Si 6 O 17 ) 2 (OH, F) 8 · 5H 2 O, Hiortdahlite I , Na 4 Ca 8 Zr 2 (Nb, Mn, Ti, Fe, Mg, Al) 2 (Si 2 O 7 ) 4 O 3 F 5 , Janhaugite , (Na, Ca) 3 (Mn 2+ , Fe 2+ ) 3 (Ti, Zr, Nb) 2 (Si 2 O 7 ) 2 O 2 (OH, F) 2 , Låvenit , (Na, Ca) 2 (Mn 2+ , Fe 2+ ) (Zr, Ti) (Si 2 O 7 ) (O, OH, F) 2 , Normandite , NaCa (Mn, Fe) (Ti, Nb, Zr) (Si 2 O 7 ) OF, Roumait , (Ca, Na, REE, ◻) 7 (Nb , Ti) [Si 2 O 7 ] 2 OF 3 as well as tienshanite , KNa 3 Na 6 Ca 2 Ba 6 Mn 6 (Ti 4+ , Nb) 6 B 12 Si 36 O 114 (O, OH, F) 11 , chemically similar Compositions on.

The assumption of only Ca 2+ in the A position leads to the ideal fluoroccalciopyrochlore “end link” composition Ca 2 Nb 2 O 6 F, which is not electrostatically neutral and therefore physicochemically not possible. A heterovalent substitution according to ( A ) Ca 2+ + ( Y ) O 2− ↔ ( A ) Na + + ( Y ) F - must have taken place, which leads to the charge-balanced end member CaNaNb 2 O 6 F. The presence of significant amounts of Ti 4+ on the B position is compensated for by an excess of Ca 2+ , corresponding to the substitution ( A ) Na + + ( B ) Nb 5+ ↔ ( A ) Ca 2+ + ( B ) Ti 4+ , which leads to the hypothetical end link Ca 2 NbTiO 6 F. In all analyzes, the amount of Ti 4+ or tetravalent cations on the B position is approximately equal to the content of 1 − Na.

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Fluorcalciopyrochlor is the Ca-dominant analogue of the Na-dominated fluoronatropyrochlore as well as the F-dominant analogue of the OH-dominated hydroxycalciopyrochlor or the O-dominated oxycalciopyrochlore. Across all subgroups, Fluorcalciopyrochlor is the Nb-dominant analogue of the Ta-dominated Fluorcalciomikrolith and the Sb 5+ -dominated Fluorcalcioroméite.

Crystal structure

Fluorcalcioyrochlore crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.4164  Å and eight formula units per unit cell . Template: room group / 227

The crystal structure of Fluorcalciopyrochlors is characterized by edge-sharing (Nb, Ti) O 6 - octahedra , which form a chain in the direction [110]. The cations Ca and Na occupy position 16 d ; they are coordinated by six oxygen and two fluorine atoms.

Fluorcalcioyrochlore 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

Fluorcalciopyrochlor occurs at its type locality mostly in the form of allotriomorphic grains or subidiomorphic crystals. Occasionally, however, the mineral also forms idiomorphic crystals up to 0.3 mm in size, which either show the octahedron, the rhombic dodecahedron or the cube as the supporting form or form combinations of these three surface forms.

physical and chemical properties

The crystals of Fluorcalciopyrochlors are brownish-yellow to reddish-orange at the type locality, but their line color is always light yellow. The mineral is brown in light transmitted through the thin section . The surfaces of the translucent to transparent Fluorcalciopyrochlors show a diamond-like sheen , which agrees well with the very high value for the light refraction (n = 2.06). On the other hand, the Fluorcalciopyrochlore crystals have a greasy sheen on fractured surfaces. Fluorcalciopyrochlor is optically isotropic.

Fluorcalciopyrochlor is neither cleavable nor divisible. Due to its brittleness , however , it breaks in a similar way to quartz , with the fracture surfaces being shell-shaped. With a Mohs hardness of 5, the mineral is one of the medium-hard minerals and, like the reference mineral apatite , can still be scratched with a pocket knife. Its Vickers hardness VHS was determined to be 424 kg / mm 2 . The calculated density for Fluorcalciopyrochlor is 4.34 g / cm³.

There is no information on fluorescence in UV light or on cathodoluminescence under the electron beam for the mineral.

Fluorcalciopyrochlor is insoluble in hydrochloric acid, HCl, and nitric acid, HNO 3 .

Education and Locations

The type locality for fluorocalciopyrochlore is the huge polygenetic REE-Fe-Nb deposit of Bayan-Obo, discovered in 1927 as an iron deposit in the Bayan-Obo mining district north of the Bayan-Obo district of the district-free city of Baotou , Inner Mongolia Autonomous Region in the People's Republic of China . The deposit is bound to carbonatites, whereby the fluorocalciopyrochlore also occurs in these carbonatites in the form of fine grains and veins together with calcite between dolomite crystals. Microstructural studies show that the mineral is bound to dolomite or calcite and that carbonates and fluorocalyopyrochlore crystallized at the same time. Possibly the mineral is the product of a metasomatosis between Ca-Mg-carbonate rocks or carbonatites as well as REE and F-rich, postmagmatic-hydrothermal solutions.

In addition to the accompanying minerals mentioned, fluorcalciopyrochlore is also found in the carbonate rocks from aegirine , riebeckite , diopside , fluorite , barite , phlogopite , britholite (Ce) , bastnesite (Ce) , zirconium , magnetite , pyrite , ferrite , columbite (Fe) , monazite - (Ce) and rutile accompanied.

Fluorcalciopyrochlore could only be described as a very rare mineral formation from around fifteen sites (as of 2018).

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

Find places for Fluorcalciopyrochlor in Austria and Switzerland are therefore unknown.

use

Fluorcalciopyrochlor would be a rich niobium ore due to its Nb 2 O 5 content of 57.71-65.21% by weight. However, due to its rarity, the mineral is of no practical importance.

See also

literature

  • 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).

Web links

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

Individual evidence

  1. ↑ 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 aa ab ac ad ae af ag ah ai aj ak al am 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).
  2. ^ A b 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]).
  3. ^ 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]).
  4. ↑ 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).
  5. ^ Donald David Hogarth: A study of pyrochlore and betafite . In: The Canadian Mineralogist . tape 6 , 1961, pp. 610–633 (English, arizona.edu [PDF; 1.6 MB ; accessed on September 27, 2018]).
  6. ↑ a b c Mindat - Fluorcalciopyrochlore , accessed on September 27, 2018 (English)
  7. ↑ Yin Jingwu, Li Guowu, Yang Guangming, Ge Xiangkun, Xu Haiming, Wang Jun: Fluornatropyrochlore, a new pyrochlore supergroup mineral from the Boziguoer rare earth element deposit, Baicheng County, Akesu, Xinjiang, China . In: The Canadian Mineralogist . tape 53 , 2015, p. 455–460 , doi : 10.3749 / canmin.1500007 (English, edu.cn [PDF; 1.6 MB ; accessed on September 24, 2018]).
  8. ↑ 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).
  9. ^ 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]).
  10. ↑ Marcelo B. Andrade, Daniel Atencio, Aba IC Persiano, Javier Ellena: Fluorcalciomicrolite, (Ca, Na, □) 2 Ta 2 O 6 F, a new microlite-group mineral from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil . In: Mineralogical Magazine . tape 77 , no. 7 , 2013, p. 2989–2996 , doi : 10.1180 / minmag.2013.077.7.08 (English).
  11. ^ Daniel Atencio, Marco E. Ciriotti, Marcelo B. Andrade: Fluorcalcioroméite, (Ca, Na) 2 Sb 5+ 2 (O, OH) 6 F, a new roméite-group mineral from Starlera mine, Ferrera, Grischun, Switzerland: description and crystal structure . In: Mineralogical Magazine . tape 77 , no. 4 , 2013, p. 467–473 , doi : 10.1180 / minmag.2013.077.4.06 (English).
  12. ↑ Mindat - Number of locations for Fluorcalciopyrochlor , accessed on September 27, 2018 (English)
  13. ↑ a b List of locations for Fluorcalciopyrochlor in the Mineralienatlas and Mindat (accessed on September 27, 2018)