Hydroxykenoelsmoreit

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Hydroxykenoelsmoreit
General and classification
other names

IMA 2016-056

chemical formula (☐, Pb) 2 (W, Fe 3+ , Al) 2 (O, OH) 6 (OH)
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.15 ( 8th edition : IV / E.02)
?
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol trigonal-rhombohedral; 3
Space group R 3 (No. 148)Template: room group / 148
Lattice parameters a  = 7.313  Å ; c  = 17.863 Å
Formula units Z  = 6
Frequent crystal faces {001}
Physical Properties
Mohs hardness ≈ 3
Density (g / cm 3 ) 5.806 (calculated)
Cleavage very perfect after {001}
Break ; Tenacity irregular; brittle
colour canary yellow
Line color pale yellow
transparency transparent
shine Glass gloss
Crystal optics
Refractive index n  = 2.065
Optical character uniaxial negative
Pleochroism none

Hydroxykenoelsmoreit is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the trigonal crystal system with the composition (☐, Pb) 2 (W, Fe 3+ , Al) 2 (O, OH) 6 (OH), so it is a Tungstat whose A position is mainly characterized by vacancies is.

Hydroxykenoelsmoreit occurs at its type locality in the form of tiny subidiomorphic , plate-like crystals with a six-sided outline of up to a maximum of 50 µm in size, which in loose clusters form rosette-shaped aggregates up to 150 µm in diameter and are associated with goethite and galena .

The type locality of the Hydroxykenoelsmoreits are hydrothermal quartz veins in the 2.5 × 15 km gold ore field of "Masaka" ( coordinates of the gold ore field of Masaka ), Muyinga Province , Burundi . Hydroxykenoelsmoreit is the first mineral whose type locality is in the Republic of Burundi.

Etymology and history

During the investigation of the crystallography and the polymorphs of secondary tungstates and antimonates in the pyrochlore upper group as well as the structures with related hexagonal tungsten bronze building blocks ("Hexagonal Tungsten Bronze", HTB), Australian mineralogists around Stuart J. Mills also researched a labeled as " Phyllotungstit " , Pittongite- like mineral with platy morphology, which turned out to be a new representative of the Elsmoreit group in the pyrochlore upper group.

The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 2016 under the provisional designation "IMA 2016-056". The first scientific description of this mineral was made in 2017 by an Australian-US-American-Russian research team with Stuart J. Mills, Andrew G. Christy , Anthony R. Kampf , Willian D. Birch and Anatoly Kasatkin in the international science magazine European Journal of Mineralogy . 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 defects (vacancies) , B position dominated by tungsten and Y position dominated by hydroxyl groups as Hydroxykenoelsmoreit ( English Hydroxykenoelsmoreite ) .

The type material for Hydroxykenoelsmoreit is kept under catalog number M53606 (holotype) in the collection of the Melbourne Museum "Museum Victoria" in Melbourne , Australia . The type grade of the Hydroxykenoelsmoreits measures only 0.5 × 0.5 cm - so far it is the only existing grade for this mineral.

Elsmoreit was the millennium in the tin - deposit Elsmore near the eponymous town in the New England region in the Australian state of New South Wales discovered and by an Australian research team led by Peter A. Williams , Peter Leverett , James L. Sharpe , Davis M. Colchester and John Rankin first described. When the nomenclature of the pyrochlore upper group was redefined, Elsmoreit was renamed Hydrokenoelsmoreit due to its chemical composition; he is also the namesake for the subgroup of the same name within the pyrochlore upper group.

classification

The current classification of the International Mineralogical Association (IMA) counts the Hydroxykenoelsmoreit 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 5+ , Nb 5+ , Ti 4+ , Sb 5+ , W 6+ , Al 3+, or Mg 2+ ; 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 Hydroxykenoelsmoreit still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydrokenopyrochlor , Hydroxycalciomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméite , Oxycalcioroméite , Oxyplumboroméite , Hydrokenoelsmoreit , Fluornatrocoulsellite and Hydrokenoralstonite . Hydroxykenoelsmoreit forms together with Hydrokenoelsmoreit within the pyrochlore upper group the Elsmoreit group .

The 8th edition of the mineral classification according to Strunz , which is now outdated, but still in use in some cases, does not yet list Hydroxykenoelsmoreit. It would belong to the mineral class of the "oxides with a metal: oxygen ratio = 2: 3 (M 2 O 3 and related compounds)", where together with anthoinite , Cerotungstit- (Ce) , (Hydrokeno) elsmoreit, Hydrotungstit , Meymacit , Mpororoit , Tungstit and Yttrotungstit- (Y) the unnamed group with the system no. IV / E.02 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), also does not yet know Hydroxykenoelsmoreit. 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. Hydroxykenoelsmoreit would be found together with Hydrokenoelsmoreit in the Elsmoreit group.

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking area , does not yet know the Hydroxykenoelsmoreit. Since this classification was created long before the redefinition of today's pyrochlore upper group, the "Elsmoreit group" is also missing.

Chemism

Four microprobe analyzes on Hydroxykenoelsmoreite grains from the type locality yielded mean values ​​of 0.03% Na 2 O; 0.03% K 2 O; 0.10% CaO; 0.03% BaO; 14.77% PbO; 1.67% Al 2 O 3 ; 5.99% Fe 2 O 3 ; 72.39% WO 3 ; and 5.45% H 2 O (calculated); Sum = 11.46%. On the basis of seven (O + OH) cations per formula unit, the empirical formula (☐ 1.668 Pb 0.315 Ca 0.009 Na 0.005 K 0.003 Ba 0.001 ) 2 = 2.00 (W 6+ 1.487 Fe 3+ 0.357 Al 0.156 ) Σ = 2.00 (O 4.119 (OH) 1.881 ) Σ = 6.00 (OH), which simplifies to (☐, Pb) 2 (W, Fe 3+ , Al) 2 (O, OH) 6 (OH) has been. This is also the official spelling of the IMA for the formula of Hydroxykenoelsmoreits.

The only minerals with the element combination W - O - H besides Hydroxykenoelsmoreit are hydrotungite , WO 3 · 2H 2 O, and Meymacite , WO 3 · 2H 2 O. Chemically similar are u. a. Jixianite , a "Plumboelsmoreit" with the formula Pb (W, Fe 3+ ) 2 (O, OH) 7 , and Mpororoit , WAlO 3 (OH) 3 · 2 (H 2 O).

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Hydroxykenoelsmoreit is the OH-dominant analogue to the H 2 O-dominated Hydrokenoelsmoreit. Across all subgroups, hydroxykenoelsmoreite is the W 6+ -dominant analogue of the Ta-dominated hydroxykenomicrolite and the Nb-dominated hydroxykenopyrochlore. The Pb contents in the A positions indicate a possible mixed crystal formation for an as yet undefined “Hydroxyplumboelsmoreit”.

Crystal structure

Hydroxykenopyrochlore crystallizes in the trigonal crystal system in the space group R 3 (space group number 148) with the lattice parameters a = 7.313  Å and c = 17.863 Å as well as six formula units per unit cell . Template: room group / 148

Hydroxykenopyrochlore is one of the non-cubic representatives of the pyrochlore upper group, in which a lowering of the symmetry splits the A , B and X positions, so that the structure crystallographically ( A 1) 3 ( A 2) 1 ( B 1) 3 ( B 2) 1 ( X 1) 6 ( X 2) 6 Y 2 corresponds. This is caused by the order of Fe 3+ on one of the two B or W positions. The Hydroxykenoelsmoreit of the type material corresponds to the polytype 3R - in contrast to the Hydrokenomikrolith-3 R (Atencio, 2016), the symmetry is reduced even further to R 3 (No. 148) . This is due to the very slight rotation of the coordination polyhedra, which is not associated with any further splitting of the positions. Template: room group / 148

The crystal structure of the Hydroxykenoelsmoreits contains B 1 octahedra with (Fe 3+ + Al) and B 2 octahedron linked via common corners . These and the lead atoms are connected to a network through the OH groups that do not belong to the framework. Both A positions are mostly empty (vacant), but partly occupied by Pb. While the B 2 position is completely occupied by tungsten, there is a substitution of tungsten by (Fe-Al) on the B 1 position.

properties

Drawing of plate-like Hydroxykenoelsmoreit crystals with the basic pinacoid {001} as the main shape and the prisms {100} (above) and {110} (below) as a further surface shape

morphology

Hydroxykenoelsmoreit forms subidiomorphic, tiny crystals of 50 µm, in most cases even less than 20 µm in diameter, with the platelet-shaped crystals reaching a thickness of only ≈ 2 µm. The crystals come together to form loose, rosette-shaped aggregates approx. 150 µm in diameter. The costume determining shape of the crystals is the Basispinakoid {001}. Although further surface shapes could not be identified, due to the appearance of the six-sided tabular crystals, prisms such as {100} or {110} must also appear (cf. the adjacent crystal drawings ).

physical and chemical properties

The crystals of the Hydroxykenoelsmoreits are canary yellow, but their line color is always pale yellow. The surfaces of the transparent Hydroxykenoelsmoreits show a glass-like gloss , which agrees well with the high value for the mean refraction (n = 2.065, calculated). The mineral is optically uniaxial negative and not pleochroic .

Hydroxykenoelsmoreit shows a very perfect cleavage according to {001}. Due to its brittleness , however , it breaks like amblygonite , with the fracture surfaces being uneven (irregular). With a Mohs hardness of ≈ 3, the mineral is one of the medium-hard minerals and, like the reference mineral calcite, could be scratched with a copper coin if the crystal size was appropriate. The calculated density for Hydroxykenoelsmoreite is 5.806 g / cm³. Information on possible fluorescence and cathodoluminescence under the electron beam is missing for the mineral, as is a characteristic of its chemical behavior.

Education and Locations

The type locality for Hydroxykenoelsmoreit are hydrothermal quartz veins in the 2.5 × 15 km gold ore field of "Masaka" in the Muyinga province in the African landlocked state of Burundi. The gold- quartz veins sit on a horizon with quartzites and quartzitic conglomerates . Artisanal mining is carried out in over 40 mines in the gold field mentioned .

Typical accompanying minerals of Hydroxykenoelsmoreite at its type locality are goethite and galena as well as quartz .

As an extremely rare mineral formation, the Hydroxykenoelsmoreit could so far (as of 2018) only be described by its type locality. Locations for Hydroxykenoelsmoreit in Germany , Austria and Switzerland are therefore unknown.

use

Hydroxykenoelsmoreit would be due to its WO 3 -contents 71.62 to 73.18 wt .-% a rich tungsten - bronze . Due to its extreme rarity, however, the mineral is of no practical importance and only of interest to mineral collectors.

See also

literature

Stuart J. Mills, Andrew G. Christy, Anthony R. Kampf, Willian D. Birch, Anatoly Kasatkin: Hydroxykenoelsmoreite , the first new mineral from the Republic of Burundi . In: European Journal of Mineralogy . tape 29 , no. 3 , 2017, p. 491–497 , doi : 10.1127 / ejm / 2017 / 0029-2618 (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 Stuart J. Mills, Andrew G. Christy, Anthony R. Kampf, Willian D Birch, Anatoly Kasatkin: Hydroxykenoelsmoreite , the first new mineral from the Republic of Burundi . In: European Journal of Mineralogy . tape 29 , no. 3 , 2017, p. 491–497 , doi : 10.1127 / ejm / 2017 / 0029-2618 (English).
  2. ↑ 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]).
  3. ^ 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 Peter A. Williams, Peter Leverett, James L. Sharpe, David M. Colchester, John Rankin: Elsmoreite, cubic WO3 · 0.5H2O, a new mineral species from Elsmore, New South Wales, Australia . In: The Canadian Mineralogist . tape 43 , 2005, p. 1061-1064 (English, rruff.info [PDF; 168 kB ; accessed on October 12, 2018] as "Elsmoreite").
  5. ^ IMA / CNMNC List of Mineral Names; September 2018 (PDF 1.66 MB)
  6. ↑ a b Mindat - Hydrokenopyrochlore , (accessed on October 12, 2018) (English)
  7. ↑ Anatoly Vasil'evich Voloshin, Yuriy Pavlovich Men'shikov, Yakov A. Pakhomovskiy, Lyudmila Ivanovna Polezhaeva: Cesstibtantite , (Cs, Na) SbTa 4 O 12 - a new mineral from granitic pegmatites . In: Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva . tape 116 , 1981, pp. 345–351 (Russian, rruff.info [PDF; 677 kB ; accessed on August 30, 2018] Abstract in: American Mineralogist (PDF; 786 kB), 1982, 67, pp. 413–414).
  8. ↑ Anatoly Vasil'evich Voloshin, Yuriy Pavlovich Men'shikov, Yakov A. Pakhomovskiy, Lyudmila Ivanovna Polezhaeva: Cesstibtantite , (Cs, Na) SbTa 4 O 12 - a new mineral from granitic pegmatites . In: International geology review . tape 24 , no. 7 , 1982, pp. 345-351 , doi : 10.1080 / 00206818209449624 (English).
  9. ↑ Ritsuro Miyawaki, Koichi Momma, Satoshi Matsubara, Takashi Sano, Masako Shigeoka, Hiroyuki Horiuchi: Hydroxykenopyrochlore, IMA 2017-030a. CNMNC Newsletter No. 39, October 2017, page 1285 . In: Mineralogical Magazine . tape 81 , 2017, p. 1279-1286 (English).
  10. ↑ Mindat - Number of locations for Hydrokenopyrochlore , (accessed on October 12, 2018) (English)
  11. ↑ List of locations for hydrokenopyrochlore from the Mineralienatlas and Mindat (accessed on October 12, 2018)