Hydroxycalciomicrolite

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Hydroxycalciomicrolite
General and classification
other names

IMA 2013-073

chemical formula Ca 1.5 Ta 2 O 6 (OH)
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 pentagon-icositetrahedral; 432
Space group P 4 3 32 (No. 212)Template: room group / 212
Lattice parameters a  = 10.4205  Å
Formula units Z  = 8
Frequent crystal faces {111}, {110}
Twinning no
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) 6.176 (calculated)
Cleavage no
Break ; Tenacity clamshell; brittle
colour yellow, colorless in transmitted light
Line color White
transparency translucent
shine Glass to resin gloss
Crystal optics
Refractive index n  = 2.010 (calculated)
Optical character isotropic

Hydroxycalciomicrolite is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition of Ca 1.5 Ta 2 O 6 (OH), that is a calcium - tantalate with additional hydroxide .

Hydroxycalciomicrolite 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 . Its type locality is the pegmatite "Volta Grande" ( coordinates of the pegmatite "Volta Grande" ) near Nazareno in Minas Gerais , Brazil.

Etymology and history

In the “Museu de Geociências”, Universidade de São Paulo, investigations of a heavy mineral concentrate called “Djalmait” from the pegmatite “Volta Grande” near Nazareno in the Brazilian state of Minas Gerais isolated ten crystals, which after determination of the physical, chemical and X-ray diffractometric properties were isolated proved to be the new representative of the new pyrochlore upper group (pyrochlore supergroup). The same heavy mineral concentrate had already provided the type material for fluoroccalciomicrolite and hydrokenomicrolite. The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 2013 under the provisional designation "IMA 2013-073". The first scientific description of this mineral was made in 2017 by an international research team with the Brazilian mineralogist Marcelo B. Andrade and Hexiong Yang , Daniel Atencio , Robert T. Downs , Nikita V. Chukanov , Marie-Hélène Lemée-Cailleau , Aba Israel Cohen Persiano , Andrés E. Goeta and Javier Ellena 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 a dominated by calcium A position, by Ta dominated B position, as well as OH - dominated Y position as Hydroxycalciomikrolith ( English Hydroxycalciomicrolite ).

The type material for hydroxycalciomicrolite is stored under catalog number DR917 (Cotyp) 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. A cotype was also deposited as part of the “RRUFF Project” (catalog number R130269) in the “University of Arizona Mineral Museum” at the University of Arizona in Tucson , Arizona , United States of America .

classification

The current classification of the International Mineralogical Association (IMA) counts the hydroxycalciomicrolite 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 Hydroxycalciomikrolith still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Hydroxycalciomicrolite, together with fluorocalciomicrolite, fluoronatromicrolite, hydrokenomicrolite, 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 hydroxycalciomicrolite. 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 force since 2001 and is used by the International Mineralogical Association (IMA), does not yet know the hydroxycalciomicrolite 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.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , does not yet know the hydroxycalciomicrolite. 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

Thirteen microprobe analyzes on hydroxycalciomicrolite from the "Volta Grande" pegmatite resulted in mean values ​​of 0.36% Na 2 O; 15.64% CaO; 0.12% MnO; 0.26% SnO 2 ; 2.82% Nb 2 O 5 ; 78.39% Ta 2 O 5 ; 0.12% F and 1.30% H 2 O (determined from crystal structure data) [(O ≡ F) -0.30%, total = 99.31%]. On the basis of two cations on the B position, the empirical formula (Ca 1.48 Na 0.06 Mn 0.01 □ 0.45 ) Σ = 2.00 (Ta 1.88 Nb 0.11 Sn 0, 01 ) Σ = 2.00 O 6 [(OH) 0.76 F 0.20 O 0.04 ], which has been simplified to the charge-balanced formula with the end link composition Ca 1.5 Ta 2 O 6 (OH). This ideal formula requires contents of 15.72% CaO; 82.60% Ta 2 O 5 ; 1.68% H 2 O (total 100.00%).

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Hydroxycalciomicrolite is the Ca-dominant analogue to the □ -dominated hydroxykenomicrolite and the OH-dominant analogue to the F-dominated fluorocalyomicrolite. Across all subgroups, hydroxycalciomicrolite is the Ta-dominant analogue of the Nb-dominated hydroxycalciopyrochlore and the Sb-dominated hydroxycalcioroméite.

Are also chemically similar to the minerals Rynersonit , Calciotantit , the discredited because identical with Calciotantit "Ungursait" and the not yet defined as a mineral " Oxycalciomikrolith " .

Crystal structure

Hydroxycalciomikrolith crystallizes in the cubic crystal system in the space group P 4 3 32 (space group no. 212) with the lattice parameter a = 10.4205  Å and eight formula units per unit cell . Template: room group / 212

Hydroxycalciomicrolite is the first natural representative of the pyrochlore upper group with an extensive order of Ca and ◻ on the A position, which reduces the symmetry (from Fd 3 m (No. 227) to P 4 3 32 (No. 212) ) has the consequence. Template: room group / 227Template: room group / 212

As with all representatives of the pyrochlore upper group, the crystal structure of the hydroxycalciomicrolite 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 hydroxide ions and the atoms such as Ca and Na in the A position.

properties

Costume and habitus of hydroxycalciomicrolite crystals
Hydroxykenomicrolite Octahedron.png
Hydroxycalciomicrolite, octahedron
Hydrokenomicrolite Octahedron Rhombendododecahedron.png
Hydroxycalciomicrolite, octahedron modified by rhombic dodecahedron

morphology

Hydroxycalciomicrolite was found in its type locality only within a heavy mineral concentrate. It occurred here in the form of crystals up to 1.5 mm in size, whose costume consists either only of the octahedron {111} or of crystals on which the surfaces of the octahedron and the rhombic dodecahedron {110} are roughly in equilibrium (cf. the crystal drawings opposite). The crystals are homogeneous and have no inclusions of other minerals.

physical and chemical properties

The crystals of hydroxycalciomicrolite are yellow, but their line color is always white. The surfaces of the translucent hydroxycalciomicrolite show a glass-like to resinous gloss , which agrees well with the very high value for the refraction of light (n = 2.040, calculated). Under the microscope the mineral is colorless in transmitted light and without abnormal anisotropy, but shows a very high surface relief.

Hydroxycalciomicrolite 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 5 to 6, the mineral is one of the medium-hard minerals and, like the reference minerals apatite (hardness 5), can be scratched with a pocket knife and orthoclase (hardness 6) with a steel file. The calculated density for hydroxycalciomicrolite is 6.176 g / cm³. Hydroxycalciomikrolith is neither in the long wavelength even in the short wavelength UV light , a fluorescent nor cathodoluminescence under the electron beam.

Education and Locations

Hydroxycalciomicrolite was found in a heavy mineral concentrate of a zoned rare metal pegmatite rich in lithium and rubidium , so that its genetic position is unclear. In general, the hydroxycalciomicrolite within the "Volta Grande" pegmatite is an accessory component.

Typical accompanying minerals of the hydroxycalciomicrolite in its type material, the “Djalmait” heavy mineral concentrate from the pegmatite “Volta Grande”, are fluorocalciomicrolite and hydrokenomicrolite. Albite , almandine , amphibole , beryl , bityite , brookite , cassiterite , epidote , fluorite , fluorapatite , gahnite , goethite , hematite , ixiolite , " lepidolite " , magnetite , microcline , " microlite " , monazite are known from similar heavy mineral concentrates from this pegmatite. (Ce) , muscovite , “ pyrochlore ” , quartz , rutile , samarskite (Y) , spodumene , tantalite (Mn) , “ tourmaline ” , “ varlamoffite ” , xenotime (Y) and zircon .

As a very rare mineral formation, the hydroxycalciomicrolite could only be described from nine sites so far (as of 2018). The type locality for hydroxycalciomicrolite is the pegmatite "Volta Grande" near Nazareno in the pegmatite province " São João del-Rei ", Minas Gerais , Brazil .

Further findings are:

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

See also

literature

  • Marcelo B. Andrade, Hexiong Yang, Daniel Atencio, Robert T. Downs, Nikita V. Chukanov, Marie-Hélène Lemée-Cailleau, Aba Israel Cohen Persiano, Andrés E. Goeta, Javier Ellena: Hydroxycalciomicrolite, Ca 1.5 Ta 2 O 6 ( OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil . In: Mineralogical Magazine . tape 81 , no. 3 , 2017, p. 555–564 , doi : 10.1180 / minmag.2016.080.116 (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 Marcelo B. Andrade, Hexiong Yang, Daniel Atencio, Robert T. Downs, Nikita V. Chukanov, Marie-Hélène Lemée-Cailleau, Aba Israel Cohen Persiano, Andrés E. Goeta, Javier Ellena: Hydroxycalciomicrolite, Ca 1.5 Ta 2 O 6 (OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil . In: Mineralogical Magazine . tape 81 , no. 3 , 2017, p. 555–564 , doi : 10.1180 / minmag.2016.080.116 (English).
  2. ↑ a b c d e Mindat - Hydroxycalciomicrolite , accessed on September 4, 2018 (English)
  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. ^ 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. ↑ Marcelo B. Andrade, Daniel Atencio, Aba IC Persiano and 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).
  6. ^ 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 .
  7. ↑ Mindat - number of sites for Hydroxycalciomikrolith , accessed on September 4, 2018 (English)
  8. ↑ Find location list for Hydroxycalciomikrolith in the Mineralienatlas and Mindat (accessed on September 4, 2018)
  9. ↑ 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).
  10. ↑ 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 2000, p. 1–193 ( uni-mainz.de [PDF; 18.9 MB ; accessed on August 25, 2018]).