Hydrokenomicrolite

from Wikipedia, the free encyclopedia
Hydrokenomicrolite
General and classification
other names
  • IMA 2011-103
  • Bariomicrolite
  • Rijkeboerit
  • Parabariomicrolite
chemical formula (◻, H 2 O) 2 Ta 2 (O, OH) 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.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  = 10.454  Å
Formula units Z  = 8
Frequent crystal faces {111}, {110}
Twinning no
Physical Properties
Mohs hardness 4.5 to 5; VHS 100g  = 485-498 kg / mm²
Density (g / cm 3 ) 6,666 (calculated)
Cleavage no
Break ; Tenacity clamshell; brittle
colour pink brown
Line color White
transparency translucent
shine Diamond to resin gloss
Crystal optics
Refractive index n  = 2.141 (measured); 2.055 (calculated)
Optical character isotropic

Hydrokenomicrolite is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition (◻, H 2 O) 2 Ta 2 (O, OH) 6 (H 2 O).

Hydrokenomicrolite is found in the form of idiomorphic, homogeneous, octahedral crystals up to 1.5 mm in size in a pegmatite in the tin - tantalum- rich pegmatite province " São João del-Rei " in Brazil . Common type localities are the pegmatite "Volta Grande" ( coordinates of the pegmatite "Volta Grande" ) near Nazareno in Minas Gerais , as well as the pegmatite "Alto do Giz" near Equador in the pegmatite province "Borborema", Rio Grande do Norte , both in Brazil.

Etymology and history

Crystals were discovered in heavy mineral concentrates from the pegmatite “Volta Grande” near Nazareno in the Brazilian state of Minas Gerais, which after determination of the physical, chemical and X-ray diffractometric properties turned out to be the new representatives of the new pyrochlore upper group (pyrochlore supergroup). The new mineral was submitted to the International Mineralogical Association (IMA), which recognized it in November 2011 under the provisional designation "IMA 2011-103". The first scientific description of this mineral was made in 2013 by a Brazilian-Russian research team with Marcelo B. Andrade , Daniel Atencio , Nikita V. Chukanov and Javier Ellena in the US science magazine "The American 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 vacancies , B position dominated by Ta and Y position dominated by H 2 O as hydrokenomicrolite ( English hydrokenomicrolite ).

In 2010, the IMA presented a new nomenclature for the minerals of the newly defined pyrochlore upper group or pyrochlore supergroup. "Hydrokenomicrolite" was already advised therein and reference was made to existing chemical data. It was listed as a recognized mineral in 2013 by Andrew G. Christy & Daniel Atencio. During the redefinition of the pyrochlore upper group, it was found that both the "Bariomicrolite" by Donald D. Hogarth (1977) and the "Rijkeboerite" by Adriaan Hendrik van der Veen (1963) do not contain enough barium to allow a possible designation as " Hydrobariomicrolite ” to justify. The “bariomicrolite” type level is □ dominant on the A position and H 2 O dominant on the Y position , so that it is probably also hydrokenomicrolite. The term “bariomicrolite” has been discredited. The “bariomicrolite” examined by Hartmut Beurlen and colleagues in 2005 is probably also hydrokenomicrolite.

The "parabariomicrolite" described in 1986 by T. Scott Ercit, Petr Černý and Frank C. Hawthorne has proven to be identical to the polytype hydrokenomicrolite-3 R ; the name “parabariomicrolite” was therefore also discredited. As a result of the “parabariomicrolite” being discredited , the hydrokenomicrolite has two common type localities . In addition to the pegmatite “Volta Grande” (type locality for the polytype hydrokenomicrolite-3 C ), this is also the pegmatite “Alto do Giz” (type locality for the polytype hydrokenomicrolite- 3R ) in Equador Co. in the Brazilian state of Rio Grande do Norte , which is 2 km south of the main road connecting the two cities of Equador and Parelhas .

The type material for hydrokenomicrolite is under the catalog number DR725 (Cotype, polytype hydrokenomicrolite-3 C ) in the collection of the "Museu de Geociências" at the "Instituto de Geociências", Universidade de São Paulo in São Paulo , State of São Paulo (federal state) , Brazil , kept. The type material for the Cotyp levels of Hydrokenomikroliths-3 R are located in the Royal Ontario Museum in Toronto , Ontario , Canada (catalog number M22607), and in the collection of the Smithsonian Institution belonging to National Museum of Natural History , Washington, DC , United States ( Catalog number 104739).

classification

The current classification of the International Mineralogical Association (IMA) counts the hydrokenomicrolite 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 Hydrokenomikrolith still Fluorcalciomikrolith , Fluornatromikrolith , Hydroxykenomikrolith , Hydroxycalciomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Hydrokenomicrolite, together with fluorocalciomicrolite, fluoronatromicrolite, hydroxycalciomicrolite, hydroxykenomicrolite, kenoplumbomicrolite, oxynatromicrolite, 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 in some cases, does not yet list the hydrokenomicrolite. 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 it might belong together with bariomicrolite (discredited 2010) Hydrokenomikrolith, 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), classifies the hydrokenomicrolite in the category of "Oxides with the molar ratio of 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 ”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. Hydrokenomicrolite can be found in the group together with fluorocalciomicrolite, fluoronatromicrolite, hydroxykenomicrolite, hydromicrolite, kenoplumbomicrolite, oxycalciomicrolite, oxystannomicrolite (formerly stannomicrolite ) and oxystibiomicrolite (formerly stibiomicrolite ).

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , does not yet know the hydrokenomicrolite. Just like the now discredited bariomicrolite , it would be classified in the class of "oxides and hydroxides" and there in the department 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

Three microprobe analyzes on hydrokenomicrolite from the pegmatite “Volta Grande” showed mean values ​​of 0.12% CaO; 0.27% MnO; 4.88% SrO; 8.63% BaO; 0.52% PbO; 0.52% La 2 O 3 ; 0.49% Ce 2 O 3 ; 0.55% Nd 2 O 3 ; 0.57% Bi 2 O 3 ; 4.54% UO 2 ; 0.18% TiO 2 ; 2.60% SnO 2 ; 2.18% Nb 2 O 5 ; 66.33% Ta 2 O 5 ; 0.46% SiO 2 ; 0.67% Cs 2 O and 4.84% H 2 O (determined by gas chromatography ). On the basis of two cations on the B position, the empirical formula [ 0.71 (H 2 O) 0.48 Ba 0.33 Sr 0.27 U 0.10 Mn 0.02 Nd 0.02 Ce 0 , 02 La 0.02 Ca 0.01 Bi 0.01 Pb 0.01 ] Σ = 2.00 (Ta 1.75 Nb 0.10 Sn 0.10 Si 0.04 Ti 0.01 ) Σ = 2, 00 [O 5.77 (OH) 0.23 ] Σ = 6.00 [(H 2 O) 0.97 Cs 0.03 ] Σ = 1.00 determined, which leads to (◻, H 2 O) 2 Ta 2 (O, OH) 6 (H 2 O) has been simplified. The charge-balanced end link has the composition ◻ 2 Ta 2 [O 4 (OH) 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. Hydrokenomicrolite is the H 2 O-dominant analogue of the OH-dominated hydroxykenomicrolite. He can z. B. can also be understood as the defect -dominant and H 2 O-dominant analogue of the O- and Sn 2+ -dominated oxystannomicrolite or the O- and Sb 3+ -dominated oxystibiomicrolite. Across all subgroups, hydrokenomicrolite is the Ta-dominant analogue of the W-dominated hydrokenoelsmoreit.

Crystal structure

Hydrokenomicrolite crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.454  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 hydrokenomicrolite 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 direction 110, which take up the water molecules and the atoms in the A position such as Ba and Sr. The Ta (O, OH) 6 octahedra are linked to one another across all corners.

properties

Costume and habit of hydrokenomicrolite crystals
Hydroxykenomicrolite Octahedron.png
Hydrokenomicrolite, octahedron
Hydrokenomicrolite Octahedron Rhombendododecahedron.png
Hydrokenomicrolite, octahedron modified by a rhombic dodecahedron

morphology

Hydrokenomicrolite was found at its type locality only within heavy mineral concentrates. It occurred here in the form of 0.2 to 1.5 mm large crystals, whose costume consists either only of the octahedron {111} or of the octahedron modified by small areas of the rhombic dodecahedron {110} (compare the adjacent crystal drawings). The crystals are homogeneous and have no inclusions of other minerals. Bariomicrolite was found in adhesions with “microlith” and is at least partially metamictic. “Parabariomicrolite” forms individual crystals up to 0.1 mm in size, which topotactically displace “microlite” crystals up to 1 cm in size .

physical and chemical properties

The crystals of the hydrokenomicrolite are pink-brown, while their line color is always white. The surfaces of the translucent hydrokenomicrolite show a resin-like to diamond-like sheen , which corresponds very well with the very high value for light refraction (n = 2.141 (measured); n = 2.055 (calculated)).

Hydrokenomicrolite shows no cleavage . 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 4.5 to 5, the mineral is one of the medium-hard minerals and, like the reference mineral apatite, can be scratched more or less well with a pocket knife. The Vickers hardness was determined with VHS 100g  = 485-498 kg / mm². The calculated density for hydrokenomicrolite is 6.666 g / cm³. Hydrokenomikrolith is neither in the long wavelength even in the short wavelength UV light , a fluorescent .

Modifications and varieties

In addition to the cubic polytype Hydrokenomicrolith-3 C , for which the properties in the information box above apply, there is also a trigonal polytype with Hydrokenomicrolith-3 R. This polytype crystallizes in the trigonal crystal system in the space group R 3 m (space group no. 166) with the lattice parameters a = 7.4290  Å and c = 18.505 Å as well as three formula units per unit cell . Template: room group / 166

Hydrokenomicrolite-3 R has the empirical formula [□ 1.49 Ba 0.36 Na 0.07 Sr 0.04 K 0.03 Pb 0.01 ] Σ = 2.00 (Ta 1.94 Nb 0.06 ) Σ = 2.00 [O 4.92 (OH) 1.08 ] Σ = 6.00 (H 2 O) 1.00 , which idealizes to □ 2 Ta 2 [O, (OH)] 6 (H 2 O) can be.

Education and Locations

Hydrokenomicrolite was found in heavy mineral concentrates from a zoned rare metal pegmatite rich in lithium and rubidium , so that its genetic position is unclear. Since there are adhesions between fluoroccalciomicrolite and hydrokenomicrolite, the assumption would be that hydrokenomicrolite is an alteration product of fluorocalciomicrolite. However, all known crystals of hydrokenomicrolite are homogeneous, which speaks against such an assumption. “Bariomicrolite” was also only first described from heavy mineral concentrates , where it forms adhesions with microlite . On the other hand, “Parabariomicrolith” was described as a topotactic displacement of microlithic crystals. Overall, there are more indications for secondary education. In general, the hydrokenomicrolite within the "Volta Grande" pegmatite is an accessory component.

Typical accompanying minerals of the hydrokenomicrolite at the type locality are fluorocalciomicrolite as well as microcline , albite , quartz , muscovite , spodumene , " lepidolite " , cassiterite , tantalite (Mn) , monazite (Ce) , fluorite , " apatite " , beryl , " garnet " , Epidote , magnetite , gahnite , zircon, “ tourmaline ” and bityite . For Bariomikrolith be as Begleitminerale Mikrolith , " tantalite " , cassiterite, quartz and " feldspar " , for Parabariomicrolith contrast Mikrolith , Simpsonit , "tantalite" , Tantalit- (Mn), Tapiolite , Natrotantit , Alumotantit , Stibiotantalit , beryl, spodumene and Petalitos specified .

As a very rare mineral formation, the two polytypes of the hydrokenomicrolite could be described so far (as of 2018) from three sites. The type locality for hydrokenomicrolite-3 C is the pegmatite “Volta Grande” near Nazareno in the pegmatite province “ São João del-Rei ”, Minas Gerais , Brazil . The type locality for hydrokenomicrolite-3 R , however, is the pegmatite "Alto do Giz" near Equador in the pegmatite province "Borborema", Rio Grande do Norte , also in Brazil. As a type locality for the former bariomicrolite or Rijkeboerite , the "Claim Chi-Chico" near Nazareno in the pegmatite province of São João del-Rei, Minas Gerais, Brazil, represented another location for hydrokenomicrolite.

Sites for hydrokenomicrolite from Germany , Austria and Switzerland are therefore unknown.

See also

literature

  • Marcelo B. Andrade, Daniel Atencio, Nikita V. Chukanov, Javier Ellena: Hydrokenomicrolite, ( ◻, H 2 O) 2 Ta 2 (O, OH) 6 (H 2 O), a new microlite-group mineral from Volta Grande pegmatite , Nazareno, Minas Gerais, Brazil . In: The American Mineralogist . tape 98 , no. 6 , 2013, p. 292–296 , doi : 10.2138 / am.2013.4186 (English).
  • Hydrokenomicrolite . 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; 120 kB ; accessed on September 3, 2018]).

Web links

Commons : Hydrokenomicrolite  - collection of pictures, 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 Marcelo B. Andrade, Daniel Atencio, Nikita V. Chukanov, Javier Ellena: Hydrokenomicrolite, ( ◻, H 2 O) 2 Ta 2 (O, OH) 6 (H 2 O), a new microlite-group mineral from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil . In: The American Mineralogist . tape 98 , no. 6 , 2013, p. 292–296 , doi : 10.2138 / am.2013.4186 (English).
  2. ^ A b c Adriaan Hendrik van der Veen: A study of pyrochlore . In: Verhandelingen van het Koninklijk Nederlands Geologische Mijnbouwkundig Genootschap. Geological series . tape 22 , 1963, pp. 1–188 (English, abstract in: American Mineralogist (PDF; 608 kB), 1963, 48, p. 1413).
  3. ^ 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]).
  4. ^ 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]).
  5. ^ 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. ↑ Hartmut Beurlen, Dwight R. Soares, Rainer Thomas, Lucila E. Prado-Borges, Cláudia de Castro: Mineral chemistry of tantalate species new in the Borborema Pegmatitic Province, Northeast Brazil . In: Anais da Academia Brasileira de Ciências (Annals of the Brazilian Academy of Sciences) . tape 77 , no. 1 , 2005, p. 923–924 , doi : 10.1590 / S0001-37652005000100013 (English, scielo.br [PDF; 476 kB ; accessed on September 3, 2018]).
  7. ^ A b c d T. Scott Ercit, Petr Černý, Frank C. Hawthorne: Parabariomicrolite, a new species, and its structural relationship to the Pyrochlore Group . In: The Canadian Mineralogist . tape 24 , 1986, pp. 655–663 (English, rruff.info [PDF; 937 kB ; accessed on September 3, 2018]).
  8. ↑ a b c d Daniel Atencio: Parabariomicrolite discredited as identical to hydrokenomicrolite-3R . In: Mineralogical Magazine . tape 80 , no. 5 , 2016, p. 923–924 , doi : 10.1180 / minmag.2016.080.129 (English).
  9. ^ 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 .
  10. ↑ a b Bariomicrolite . 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; 68  kB ; accessed on September 3, 2018]).
  11. ↑ a b c d Parabariomicrolite . 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 September 3, 2018]).
  12. ↑ Mindat - Number of locations for hydrokenomicrolite , accessed on September 3, 2018 (English).
  13. ↑ List of locations for hydrokenomicrolite in the Mineralienatlas and Mindat (accessed on September 3, 2018).
  14. ↑ Henrique Senna Diniz Pinto: Pyrochlore of the pegmatite province Nazareno / Brazil: Model concepts for mineralization - alteration - crystal chemistry (dissertation, department of geosciences, Johannes Gutenberg University) . Johannes Gutenberg University Mainz, Mainz 2000, p. 1–193 ( uni-mainz.de [PDF; 18.9 MB ; accessed on August 25, 2018]). Pyrochlore from the pegmatite province of Nazareno / Brazil: Model ideas for mineralization - alteration - crystal chemistry (dissertation, Department of Geosciences, Johannes Gutenberg University) ( Memento from September 4, 2018 in the Internet Archive )
  15. ^ Hydrokenomicrolite . 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; 120  kB ; accessed on September 3, 2018]).
  16. ↑ a b Mindat - Hydrokenomicrolite , accessed on September 3, 2018 (English).