Hydrokenopyrochlore

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Hydrokenopyrochlore
General and classification
other names

IMA 2017-005

chemical formula (◻, #) 2 Nb 2 O 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  = 10.4887  Å
Formula units Z  = 8
Frequent crystal faces {111}
Physical Properties
Mohs hardness not definable
Density (g / cm 3 ) 5.08 (calculated)
Cleavage not definable
Break ; Tenacity irregular
colour light brown to beige
Line color White
transparency not definable
shine Resin gloss
Crystal optics
Refractive index n  = 2.074
Optical character isotropic

Hydrokenopyrochlore is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition (◻, #) 2 Nb 2 O 6 · H 2 O, so it is a niobate whose A position is mainly characterized by vacancies.

Hydrokenopyrochlore occurs at its type locality in the form of subidiomorphic , octahedral crystals with a maximum size of 1 mm, which are closely associated with quartz , orthoclase , minerals of the mica group , hebnerite and a red tourmaline .

The type locality is of the Hydrokenopyrochlors at an altitude of 1300 m at the mountain Ibity lying complex lithium - cesium - tantalum -Pegmatit (LCT pegmatite) "Antandrokomby" ( coordinates of the Antandrokomby-pegmatite ) of Pegmatitfelds Sahatany in the southern part, Manandona -Tal , Vakinankaratra region , former Antananarivo province , Madagascar , the u. a. became known as the first place of discovery for the minerals londonite and manandonite .

Etymology and history

During a preliminary scanning electron microscope examination of pyrochlore samples from granite pegmatites in Madagascar, crystals from the pegmatite "Antandrokomby" in Madagascar with very high levels of cesium were identified, whereupon a more detailed chemical analysis of these samples was carried out. Due to stereochemical constraints, the occurrence of cesium is linked to the existence of “inverse pyrochlores” - in which very large cations such as cesium are located in the Y position instead of anions as in “normal” pyrochlores . Such pyrochlores are rare in nature and, with cesiokenopyrochlor, only such a representative of the pyrochlore upper group is known. The quantitative chemical analysis of the Cs-rich crystals in combination with crystal structure refinements showed, however, that the amount of cesium was not sufficient for a dominance on the Y position. Regardless of this, due to the dominance of vacancies on the A position and the slight predominance of H 2 O on the Y position, it is a previously unknown representative of the pyrochlore upper group and thus a new mineral.

The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 2017 under the provisional designation "IMA 2017-005". The first scientific description of this mineral was made in 2018 by an Italian-Swiss research team with Cristian Biagioni , Nicolas Meisser , Fabrizio Nestola , Marco Pasero , Martin Robyr , Philippe Roth , Cédric Schnyder and Reto Gieré 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 vacancies , a B position dominated by niobium and a Y position dominated by water as hydrokenopyrochlore ( English Hydrokenopyrochlore ) .

The type material for hydrokenopyrochlore is listed under catalog numbers MGL 080141 and 080142 (cotypes) in the mineralogical collection of the “Musée cantonal de géologie de Lausanne” in Lausanne , Switzerland and in the mineralogical collection of the “Museo di Storia Naturale” at the University of Pisa in Pisa , Italy , (catalog number 19905).

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

The 8th edition of the mineral classification according to Strunz , which is now outdated, but in some cases still in use, does not yet list hydrokenopyrochlore. 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), also does not yet know hydrokenopyrochlore. 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. Hydrokenopyrochlor would be doing with Fluorcalciopyrochlor , Fluornatropyrochlor , Fluorkenopyrochlor , Fluorstrontiopyrochlor , Hydropyrochlor (formerly Kalipyrochlor ) Hydroxycalciopyrochlor , Kenoplumbopyrochlor , Oxycalciopyrochlor (formerly Stibiobetafit ) Oxynatropyrochlor , Oxyplumbopyrochlor and Oxyyttropyrochlor- (Y) 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 hydrokenopyrochlore. 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

Twelve microprobe analyzes on hydrokenopyrochlore grains from the type locality yielded mean values ​​of 8.14% WO 3 ; 14.33% Sb 2 O 5 (total) [resp. 1.71% Sb 2 O 5 and 11.37% Sb 2 O 3 ]; 44.09% Nb 2 O 5 ; 13.97% Ta 2 O 5 ; 0.51% SiO 2 ; 0.21% SnO 2 ; 0.86% CaO; 0.04% MnO; 1.79% Na 2 O; 14.47% Cs 2 O and 2.23% H 2 O (calculated); Total = 99.39%. On the basis of two cations in the B position per formula unit, the empirical formula (◻ 1.32 Sb 3+ 0.35 Na 0.26 Ca 0.07 ) Σ = 2.00 (Nb 1.47 Ta 0 , 28 W 0.16 Sb 5+ 0.05 Si 0.04 ) Σ = 2.00 O 6 [(H 2 O) 0.55 Cs 0.45 ], resulting in ◻ 2 Nb 2 O 4 (OH ) 2 (H 2 O) has been simplified. This simplified formula requires contents of 88.06% Nb 2 O 5 and 11.94% H 2 O. Since no OH groups were detected in the examined material, the ideal formula for hydrokenopyrochlore should be (◻, #) 2 Nb 2 O 6 · H 2 O can be written, where “#” denotes an unspecified substituent necessary for charge equalization.

The only mineral besides hydrokenopyrochlore with the element combination Nb - O - H is hydroxykenopyrochlore, (□, Ce, Ba) 2 (Nb, Ti) 2 O 6 (OH, F). Chemically similar are 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. Hydrokenopyrochlore is the H 2 O-dominant analogue to the OH-dominated hydroxykenopyrochlore and to the Cs-dominated cesiokenopyrochore as well as the vacancy-dominant analogue to the H 2 O-dominated hydropyrochlore. Across all subgroups, hydrokenopyrochlore is the Nb-dominant analogue of the Ta-dominated hydroxykenomicrolite and the W 6+ -dominated hydroxykenoelsmoreit.

The type of hydrokenopyrochloride is chemically an intermediate member of the mixed crystal series between the ideal hydrokenopyrochlore, ◻ 2 Nb 2 O 4 (OH) 2 (H 2 O), and the ideal cesiokenopyrochlor, ◻ 2 Nb 2 (O, OH) 6 Cs 1− x (x ≈ 0.20).

Crystal structure

Hydrokenopyrochlore crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.4887  Å and eight formula units per unit cell . Template: room group / 227

The crystal structure of a three-dimensional Hydrokenopyrochlors can octahedral framework of corner-sharing B O 6 - octahedra are described, wherein in the interstices of this scaffold, the A cations and the H 2 O-groups are seated. In the B position (16 c ) there are Nb and Ta as well as some W, Sb 5+ and Si 4+ . The oxygen atoms are three-coordinate when A / A 'is vacant and Y is occupied by Cs or four-coordinate when A / A' is occupied by Na, Ca, and / or Sb and Y is occupied by H 2 O. The eight-fold coordinated A position (16 d ) is mainly empty (dominated by vacancies) and also has small amounts of Na and Ca. When A is filled with these metals, the Y position (8 b ) is occupied by an H 2 O group. The divided A 'position (96 g ) is also mainly empty, but is occupied by small amounts of Sb 3+ . In this case, the occupation of A ′ by Sb 3+ is coupled to the occupation of Y by H 2 O, which leads to a fourfold coordination of A ′. The Y position can also be occupied by Cs.

Hydrokenopyrochlore 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

Drawing of an octahedral hydrokenopyrochlore crystal

morphology

At its type locality, hydrokenopyrochlore forms subidiomorphic, octahedral crystals with a maximum size of 1 mm (compare the crystal drawing opposite). They are characteristically very porous, occasionally relictic and always closely fused with the accompanying minerals.

physical and chemical properties

The hydrokenopyrochloride crystals are tan (light brown) to beige in color, while their streak color is always white. The surfaces of the likely translucent to transparent hydrokenopyrochloride show a resinous sheen , which corresponds very well with the very high value for the refraction of light (n = 2.074). Hydrokenopyrochlore is optically isotropic.

The cleavage and divisibility was not determined nor due to the porous nature of the mineral Mohs hardness . Hydrokenopyrochlore is likely to have a similar brittleness to the other representatives of the pyrochlore upper group and therefore breaks like amblygonite , with the fracture surfaces being irregular. The calculated density for hydrokenopyrochlore is 5.08 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 Hydrokenopyrochlor is at an altitude of 1300 m on the mountain Ibity lying, complex lithium - cesium - tantalum of Pegmatitfelds Sahatany, -Pegmatit "Antandrokomby" in the southern part Manandona -Tal region Vakinankaratra in the former province of Antananarivo in Madagascar . Like all of the important pegmatites in this region, the "Antandrokomby" pegmatite is an intrusion into dolomitic marbles . The pegmatite is characterized by an enrichment of boron and belongs to the "Danburite subtype" of the LCT pegmatites. Their Cs and Rb contents correlate with the geochemical evolution of the pegmatites and are highest in the genetically most developed areas, such as the "Antandrokomby" pegmatite. The "Antandrokomby" pegmatite is a thin, steeply dipping corridor with a thickness of 1.2 m. The high cesium contents of the hydrokenopyrochloride are obviously indicative of the central miarolithic and most developed areas of the pegmatite dike within the Sahatany pegmatite field.

The exact location of the hydrokenopyrochloride in the pegmatite of Antandrokomby is unknown, but its hydrated and Cs-rich composition can be explained by one of the two processes described below:

  • primary crystallization in the central, miarolithic and geochemically most developed areas of the pegmatitic veins, in which rich occurrences of red tourmaline and Cs-containing minerals such as pollucite , londonite and Cs-rich beryl are localized
  • Secondary alteration of a Na-rich pyrochloride with high Cs + activity, which is due to the hydrothermal or supergenic alteration of a Cs-containing mineral association.

The textural features suggest rather the second mechanism, with the interaction between hypogenic pyrochlore and Cs-rich fluids leading to the leaching of the A cations.

Typical accompanying minerals of hydrokenopyrochloride at its type locality are quartz , orthoclase , minerals of the mica group , hebnerite , a still undetermined Heftetjernite -like mineral and a red tourmaline , whereby the tourmalines of Antandrokomby vary in their composition from Elbaite to Schörl .

As an extremely rare mineral formation, the hydrokenopyrochlore could so far (as of 2018) only be described from one other place of discovery in addition to its type locality worldwide. This is a Nb-Ta-rich granite pegmatite dike in the "Malá Vlčia Dolina" in the mining district of Dobšiná , Okres Rožňava , Košický kraj , Slovakia

Locations for hydrokenopyrochlore in Germany , Austria and Switzerland are therefore unknown.

use

Hydrokenopyrochlor is due to its Nb 2 O 5 -contents 39.28 to 47.02 wt .-% a rich niobium - ore . Due to its rarity, however, the mineral is of no practical importance and only of interest to mineral collectors.

See also

literature

  • 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).

Web links

Commons : Hydrokenopyrochlore  - 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 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).
  2. ↑ T. Scott Ercit, Petr Černý, Frank C. Hawthorne: Cesstibtantite - a geologic introduction to the inverse pyrochlores . In: Mineralogy and Petrology . tape 48 , 1982, pp. 235-255 , doi : 10.1007 / BF01163101 (English).
  3. ↑ a b Atali A. Agakhanov, Anatoly V. Kasatkin, Sergey N. Britvin, Oleg I. Siidra, Leonid A. Pautov, Igor V. Pekov, VY Karpenko: Cesiokenopyrochlore, IMA 2016-104. CNMNC Newsletter No. 36, April 2017, page 406 . In: Mineralogical Magazine . tape 81 , 2017, p. 403-409 (English).
  4. ↑ 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]).
  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. ↑ 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).
  7. ↑ a b Mindat - Hydrokenopyrochlore , (accessed on October 12, 2018) (English)
  8. ↑ 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).
  9. ↑ 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; 248 kB ; accessed on October 1, 2018]).
  10. ↑ 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).
  11. ↑ 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).
  12. ↑ 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").
  13. ↑ Mindat - Number of locations for Hydrokenopyrochlore , (accessed on October 12, 2018) (English)
  14. ↑ List of locations for hydrokenopyrochlore from the Mineralienatlas and Mindat (accessed on October 12, 2018)
  15. ↑ Pavel Uher, Peter Bačík, Martin Števko, Štěpán Chládek, Jana Fridrichová: Elbaite-bearing, Nb-Ta-rich granitic pegmatite from Dobšiná, Gemeric Unit, Eastern Slovakia: the first documented occurrence in the Western Carpathians . Book of Contributions and Abstracts. In: Martin Ondrejka, Jan Cempírek, Peter Bačík (eds.): Joint 5th Central-European Mineralogical Conference and 7th Mineral Sciences in the Carpathians Conference . Banská Štiavnica, June 26–30, 2018. Mineralogical Society of Slovakia and Slovak Mining Museum, Bratislava 2018, ISBN 978-80-223-4548-4 , p. 109 (English, cemc2018.com [PDF; 17.4 MB ; accessed on October 12, 2018]).