Oxynatromicrolite

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Oxynatromicrolite
General and classification
other names

IMA 2013-063

chemical formula (Na, Ca, U) 2 Ta 2 O 6 (O, F)
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.15 ( 8th edition : IV / C.18)
02/08/02. ##
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  = 10.420  Å
Formula units Z  = 8
Frequent crystal faces {111}, {110}, {100}
Physical Properties
Mohs hardness ≈ 5; VHS 100g  = 374.5-562.9 N / mm²
Density (g / cm 3 ) 6.580 (measured, not heated); 6.506 (calculated)
Cleavage no
Break ; Tenacity clamshell; brittle
colour brown, yellowish brown
Line color pale yellowish brown
transparency opaque, translucent edges
shine Greasy to wax sheen
radioactivity radioactive due to uranium content
Crystal optics
Refractive index n  = 1.999 (calculated)
Optical character isotropic
Other properties
Special features metamict by uranium content

Oxynatromicrolite is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system having the composition (Na, Ca, U) 2 Ta 2 O 6 (O, F), that is a sodium - tantalate with additional oxygen ions .

Oxynatromicrolite is found in the form of idiomorphic, homogeneous, octahedral crystals up to a maximum of 0.2 mm in size in a vein- shaped LCT granite pegmatite ( lithium - cesium - tantalum pegmatite ) in the tin- tantalum-rich "pegmatite field Guanpo" in China . Its type locality is the "pegmatite dike no . 190 km southwest of Luoyang ". 309 ”( coordinates of the“ pegmatite 309 ” ) in the pegmatite field of Guanpo near the city of the same name in Lushi County , Sanmenxia , Henan Province , China.

Etymology and history

During the investigation of the formation and the associated minerals of Luanshiweiit , a new representative of the mica , an oxidic Ta-Nb mineral with an unusual chemical composition was found among its accompanying minerals, which in the past was either “pyrochlore” according to the nomenclature of the old “pyrochlore group”. Microlite ”or“ uranium microlite ”. After determining the physical, chemical and X-ray diffractometric properties, it turned out to be a new representative of the new pyrochlore upper group (pyrochlore supergroup). The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 2013 under the provisional designation "IMA 2013-063". The first scientific description of this mineral took place in 2017 by a Chinese team of scientists with Fan Guang, Ge Xiangkun, Li Guowu, Yu Apeng and Shen Ganfu in the English science magazine "Mineralogical Magazin". 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 sodium , B position dominated by Ta and Y position dominated by O as oxynatromicrolite ( English Oxynatromicrolite ).

The type material for oxynatromicrolite is stored under catalog number M11940 (holotype) in the collection of the Chinese Geological Museum in Beijing , China.

classification

The current classification of the International Mineralogical Association (IMA) counts the oxynatromicrolite 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 Oxynatromikrolith still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydroxycalciomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméite , Oxyplumboroméite , Hydrokenoelsmoreit , Fluornatrocoulsellite and Hydrokenoralstonite . Oxynatromicrolite, together with fluorocalciomicrolite, fluoronatromicrolite, hydrokenomicrolite, hydroxycalciomicrolite, hydroxykenomicrolite, kenoplumbomicrolite, oxystibiomicrolite and oxystannomicrolite, form the microlite group within the pyrochlore upper group .

The 8th edition of the mineral classification according to Strunz , which is now outdated but still in use , does not yet list the oxynatromicrolite. 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 bariomicrolite (discredited 2010, possibly hydrokenomicrolite ) Bismutomikrolith (discredited 2010), Fluornatromikrolith , Mikrolith , Natrobistantit , Plumbomikrolith , Stannomikrolith , Stibiomikrolith and Uranmikrolith the "pyrochlore group Mikrolith subgroup" with the system number. IV / C.18 .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), does not yet know the oxynatromicrolite either. It would be classified in the department of "oxides with the molar ratio metal: oxygen = 1: 2 and comparable". This is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral is classified according to its composition and structure in the subsection “With large (± medium-sized) cations; Layers of edge-linked octahedra ”would 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 would form. Along with Fluorcalciomikrolith, Fluornatromikrolith, Hydrokenomikrolith, Hydroxykenomikrolith, Hydromikrolith, Kenoplumbomikrolith, Oxycalciomikrolith, Oxystannomikrolith would thereby Hydroxycalciomikrolith (formerly Stannomikrolith ) (formerly and Oxystibiomikrolith Stibiomikrolith ) found in the Mikrolithgruppe.

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking world , does not yet know the oxynatromicrolite. It would be placed in the class of "oxides and hydroxides" and there in the division of "multiple oxides with Nb, Ta and Ti". Here it would be in the “microlith subgroup; Ta> Nb; (Ta + Nb) > 2 (Ti) “with the system no. 02/08/02 within the subsection of " Multiple oxides with Nb, Ta and Ti with the formula A 2 (B 2 O 6 ) (O, OH, F) ".

Chemism

Eighteen microprobe analyzes on eight different oxynatromicrolite crystals from the pegmatite "Pegmatite Dike No. 309 “gave mean values ​​of 5.41% Na 2 O; 4.56% CaO; 14.00% UO 2 ; 0.16% La 2 O 3 ; 0.11% Ce 2 O 3 ; 0.13% Nd 2 O 3 ; 0.62% PbO; 61.52% Ta 2 O 5 ; 8.21% Nb 2 O 5 ; 0.23% Sb 2 O 5 ; 0.05% TiO 2 ; 0.56% SiO 2 ; 0.29% SnO 2 ; 1.04% F; -0.44% (O ≡ F) and 1.30% H 2 O (determined from the stoichiometry) [total = 98.53%]. On the basis of two cations on the B position, the empirical formula (Na 0.99 Ca 0.46 U 0.31 Pb 0.02 La 0.01 H 2 O 0.21 ) 2 = 2.00 (Ta 1.58 Nb 0.35 Si 0.05 Sn 0.01 Sb 0.01 ) Σ = 2.00 O 6 (O 0.43 F 0.31 H 2 O 0.26 ) Σ = 1.00 determined, which has been simplified to (Na, Ca, U) 2 (Ta, Nb) 2 O 6 (O, F). The ideal formula for oxynatromicrolite is (Na, Ca, U) 2 Ta 2 O 6 O.

The uranium content of 12.38-18.03% by weight UO 2 leads to a complete metamictization of the mineral.

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Oxynatromicrolite is the O-dominant analog of the F-dominated fluorine atomic microlite and the Na-dominant analog of the Sn-dominated oxystannomicrolite or the Sb-dominated oxystibiomicrolite. Irtyshite and natrotantite are chemically similar .

Crystal structure

Oxynatromicrolite is strongly metamictic due to its high content of UO 2 . The parameters for the unit cell were determined on material which was heated for four hours at 1000 ° C. in a nitrogen atmosphere and then cooled to room temperature at 10 ° C.h −1 and thereby recrystallized. They are comparable with the values ​​for other representatives of the pyrochlore upper group. Oxynatromicrolite crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.420  Å and eight formula units per unit cell . Template: room group / 227

As with all representatives of the pyrochlore upper group, the crystal structure of the oxynatromicrolite consists of - in this case - Ta (O, OH) 6 - octahedra with common corners, which form parallel layers of three and six rings [110]. In these layers there are channels in the direction <110>, which take up the oxygen atoms and the atoms such as Na, Ca and U in the A position.

properties

morphology

Oxynatromicrolite was found at its type locality in idiomorphic, comparatively tiny crystals with a diameter of 0.05 to 0.20 mm. Their costume consists either of the octahedron {111} or - much more rarely - the rhombic dodecahedron {110} or the hexahedron {100}. Occasionally, combinations of two or all three surface shapes occurred.

physical and chemical properties

Oxynatromicrolite is strongly metamictic due to its high content of UO 2 . Physical and optical parameters were determined on material which was heated for four hours at 1000 ° C in a nitrogen atmosphere .

The crystals of the oxynatromicrolite are brown or yellowish brown, while their line color is always pale yellowish brown. The surfaces of the opaque, only edge-translucent oxynatromicrolite show a greasy to waxy sheen , which agrees well with the very high value for light refraction (n = 1.999, calculated).

Oxynatromicrolite 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. The Vickers hardness was determined with VHS 100g  = 374.5-562.9 N / mm². The measured density for non-recrystallized oxynatromicrolite is 6.580 g / cm³, the calculated density is 6.506 g / cm³.

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

Education and Locations

Oxynatromicrolite is assumed to have a primary formation at its type locality due to the textural relationships to its accompanying minerals and the geological and geochemical characteristics of the pegmatite. The mineral crystallized directly from a highly developed acidic magma or from igneous-hydrothermal fluids that were rich in volatile and lihophilic ore-forming elements. Albitization, lepidolithization and the formation of old men were probably not necessary for the formation of oxynatromicrolite. In places, however, the mineral is secondarily displaced by a more hydrated phase.

Typical accompanying minerals of the oxynatromicrolite at its type locality are albite , potassium feldspar , quartz , muscovite , kaolinite , tantalite (Mn) , stibiotantalite , pollucite , spodumene , montebrasite , hafnium- rich zircon , a red " tourmaline " , polylithionite, 2 trilhiionite M 1 and the aforementioned weathering product of oxynatromicrolite.

As a very rare mineral formation, the oxynatromicrolite could so far (as of 2018) only be described from one point of discovery. The type locality for oxynatromicrolite is the vein-shaped LCT granite pegmatite "Pegmatite vein No. 309 “in the pegmatite field of Guanpo near the city of the same name in Lushi County , Sanmenxia , Henan Province , China .

Locations for oxynatromicrolite from Germany , Austria and Switzerland are therefore unknown.

In the past, two minerals have been described that are similar to oxynatromicrolite:

  • As early as 1975, Wang described from the granite pegmatite vein No. 3 in Koktokay County , Altay Governorate , Xinjiang Uyghur Autonomous Region , China, a mineral which he called "Brannerite- (Bi, Ta)" according to the old nomenclature of the pyrochlore group. Its empirical formula is (Na 0.96 Bi 0.66 U 0.21 K 0.13 Ca 0.12 Mn 0.07 Mg 0.06 ) Σ = 2.21 (Ta 0.62 Ti 0.47 Nb 0 , 35 Fe 3+ 0.30 Si 0.11 Al 0.08 ) Σ = 1.95 [O 6.35 (OH) 0.32 ] Σ = 6.67 , it became (Na, Bi, U) 2 (Ta, Ti, Nb) 2 [O 6 (O, OH)] 7 simplified.
  • Two years later, Richard H. Jahns & Rodney C. Ewing from the "Harding Mine" (Harding pegmatite) in the Picuris District, Taos County , New Mexico , United States , described a mineral with the composition (Na 0.74 Ca 0, 52 Mn 0.33 U 0.20 Pb 0.13 ) Σ = 1.92 (Ta 1.77 Nb 0.21 W 0.01 ) Σ = 1.99 O 6.73 .

With both minerals, the B, Y and A positions are mainly occupied by Ta, O and Na, which is why they should be referred to as oxynatromicrolite.

use

Oxynatromicrolite is a sought-after mineral by mineral collectors due to its rarity, but otherwise of no practical importance.

See also

literature

  • Fan Guang, Ge Xiangkun, Li Guowu, Yu Apeng and Shen Ganfu: Oxynatromicrolite, (Na, Ca, U) 2 Ta 2 O 6 (O, F), a new member of the pyrochlore supergroup from Guanpo, Henan Province, China . In: Mineralogical Magazine . tape 81 , no. 4 , 2017, p. 743–751 , doi : 10.1180 / minmag.2016.080.121 (English).

Web links

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 Fan Guang, Ge Xiangkun, Li Guowu, Yu Apeng and Shen Ganfu: Oxynatromicrolite , (Na, Ca, U) 2 Ta 2 O 6 (O, F), a new member of the pyrochlore supergroup from Guanpo, Henan Province, China . In: Mineralogical Magazine . tape 81 , no. 4 , 2017, p. 743–751 , doi : 10.1180 / minmag.2016.080.121 (English).
  2. ↑ a b c Mindat - Oxynatromicrolite , accessed on September 6, 2018 (English)
  3. ^ 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]).
  4. ^ A b c 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]).
  5. ^ 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]).
  6. ↑ Thomas Witzke, Manfred Steins, Thomas Doering, Walter Schuckmann, Reinhard Wegner, Herbert Pöllmann: Fluornatromicrolite, (Na, Ca, Bi) 2 Ta 2 O 6 F, a new mineral species from Quixaba, Paraíba, Brazil . In: The Canadian Mineralogist . tape 49 , 2011, p. 1105–1110 , doi : 10.3749 / canmin.49.4.1105 (English).
  7. ^ 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 .
  8. ↑ Mindat - Number of locations for oxynatromicrolite , accessed on September 6, 2018 (English)
  9. ↑ List of locations for oxynatromicrolite in the Mineralienatlas and Mindat (accessed on September 6, 2018)
  10. ^ XJ Wang: The primary study on Nb-Ta minerals in a pegmatite, Xinjiang . In: Anonymus (Ed.): The Treatise Collections of the National Meeting about Rare-element Geology . 1st edition. tape I . Scientific Press, Beijing 1975, pp. 145–161 (English, Chinese).
  11. ^ Richard H. Jahns, Rodney C. Ewing: The Harding Mine, Taos County, New Mexico . In: The Mineralogical Record . tape 8 , no. 2 , 1977, p. 115-1126 (English).