Oxystibiomicrolite

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Oxystibiomicrolite
General and classification
other names

Stibiomicrolite

chemical formula (Sb 3+ , Ca) 2 Ta 2 O 6 O
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.15 ( 8th edition : IV / C.18)
02/08/02/07
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  = 10.455  Å
Formula units Z  = 8
Physical Properties
Mohs hardness <5.5 (the hardness of stibiotantalite)
Density (g / cm 3 ) 5.84 to 6.22 (calculated)
Cleavage no
Break ; Tenacity uneven; brittle
colour greenish white to white; gray in reflected light
Line color White
transparency translucent
shine not specified
Crystal optics
Refractive index n  > 1.9 (measured); 2.072 to 2.163 (calculated for different compositions)
Optical character isotropic

Oxystibiomicrolite is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition (Sb 3+ , Ca) 2 Ta 2 O 6 O, so it is an antimony - tantalate with additional oxygen ions .

Oxystibiomicrolite is found in the form of extremely fine-grained aggregates (≤ 0.1 mm), which in a granite pegmatite form a displacement product of primarily formed minerals such as stibiotantalite and native antimony .

Its type locality is the pegmatite of the LCT (lithium-cesium-tantalum) type "Varuträsk" ( coordinates. ), Which has been mined since 1933, 15 km northwest of Skellefteå in the municipality of the same name Skellefteå within the Swedish province of Västerbotten County and the historical province of Västerbotten of the pegmatite Varuträsk ).

Etymology and history

The term stibiomicrolite was originally applied by Percy Dudgeon Quensel & Thelma Berggren to a hypothetical mineral, which supposedly has decayed into an intergrowth of stibiotantalite, microlite , native antimony and a little antimonite , with senarmontite as a secondary oxidation product. The mineral was introduced to the American Mineralogist in 1938 by William F. Foshag.

The name was later applied to a microlite from Varuträsk, which was apparently a decay product of stibiotantalite. However, Michael Fleischer discredited this mineral in 1942 due to the lack of reliable data on the composition, which was confirmed again by Donald David Hogarth in the first "Classification and nomenclature of the pyrochlore group" (1977).

In the course of the investigation of (Nb, Ta) -containing oxide minerals from granite pegmatites, Lee A. Groat, Petr Černý and T. Scott Ercit re-examined the association “Stibiotantalit ← Microlite + Antimony” from Varuträsk in order to examine the compositional relationships between the oxide phases using electron beam microanalysis to investigate. Their investigations showed that there is actually a microlith phase with antimony content at a level that justifies the revalidation of the stibiomicrolite under its original name. The new data for the old mineral was presented to the International Mineralogical Association (IMA), which revalidated as a stibiomicrolite in 1987.

The type material for oxystibiomicrolite is stored under catalog number 600200 (holotype) in the collection of the Naturhistoriska riksmuseet in Stockholm , Sweden, and in the Mineralogical Museum of the Department of Geological Sciences , University of Manitoba , Canada , (collection no. M6134). The original material stibiomicrolite from the adaptation by Quensel & Berggren (1938) is in the Galerie Nationale de Minéralogie et de Géologie of the Muséum national d'histoire naturelle in Paris , France (catalog no. 139984).

During the revision of the nomenclature of the "pyrochlore group" to the new pyrochlore supergroup (pyrochlore supergroup), it was determined according to the chemical composition of the stibiomicrolite that this mineral with an A position in the crystal lattice dominated by antimony ( Latin stibium ) and B dominated by Ta Position and the Y position dominated by O with the new, nomenclature-compliant name Oxystibiomicrolith ( English Oxystibiomicrolite ). The type level of the former "stibiomicrolite" became the type level of the new "oxystibiomicrolite".

classification

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

In the 8th edition of the mineral systematics according to Strunz , which is now outdated, but in some cases still in use , the stibiomicrolite, which was redefined as oxystibiomicrolite in 2010, belongs to the mineral class of "oxides and hydroxides" and there to the general section of "oxides with a metal: oxygen ratio = 2: 3 ( M 2 O 3 and related compounds) "where he together with Bariomikrolith discredited (2010), may Hydrokenomikrolith, Bismutomikrolith (discredited 2010), Fluornatromikrolith , Mikrolith , Natrobistantit , Plumbomikrolith , Stannomikrolith and Uranmikrolith the" pyrochlore group Mikrolith subgroup " with the system no. IV / C.18 .

The 9th edition of Strunz's mineral systematics, which has been valid since 2001 and is used by the International Mineralogical Association (IMA), classifies the oxystibiomicrolite (formerly stibiomicrolite ) in the department of "oxides with the molar ratio of metal: oxygen = 1: 2 and comparable" . However, this section is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “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. Oxystibiomicrolite can be found in the microlite together with fluorocalciomicrolite, fluoronatromicrolite, hydrokenomicrolite, hydromicrolite, hydroxykenomicrolite (formerly cesstibtantite ), kenoplumbomicrolite, oxycalciomicrolite and oxystannomicrolite (formerly stannomicrolite ).

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the oxystibiomicrolite (formerly stibiomicrolite ) to the class of "oxides and hydroxides", but there in the category of "multiple oxides with Nb, Ta and Ti". Here it is together with microlite, bariomicrolite, fluorine atromicrolite, plumbomicrolite, uranium microlite, bismuthomicrolite and stannomicrolite in the “microlite 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

The microprobe analysis with the highest Sb content, determined on an oxystibiomicrolite from the pegmatite “Varuträsk”, resulted in values ​​of 2.58% Na 2 O; 6.78% CaO; 52.65% Ta 2 O 5 ; 17.54% Nb 2 O 5 ; 19.24% Sb 2 O 5 [total = 98.79%]. On the basis of two cations on the B position, the empirical formula was (Sb 0.71 Ca 0.65 Na 0.45 ) Σ = 1.81 (Ta 1.29 Nb 0.71 ) Σ = 2.00 O 6 O, which was simplified to (Sb, Ca, Na) 2 Ta 2 O 6 O.

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Oxystibiomicrolite is the Sb-dominant analogue of the Na-dominated oxynatromicrolite and the Sn-dominated oxystannomicrolite.

Chemically similar are stibiotantalite, Sb (Ta, Nb) O 4 , a bismuth-containing variety of stibiotantalite, (Sb, Bi) (Ta, Nb) O 4 , and hydroxykenomicrolite, (◻, Na, Sb 3+ ) 2 Ta 2 O 6 (OH).

Crystal structure

Oxystibiomicrolite crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.455  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 oxystibiomicrolite consists of - in this case - Ta (O, OH) 6 - octahedra with common corners that form parallel layers of three and six rings [110]. In these layers there are channels in the direction of <110>, which take up the oxygen atoms and the atoms in the A position such as Sb and Ca.

properties

morphology

The most common displacement texture that the stibiotantalite from Varuträsk shows is a boxwork of composite passages that partially penetrated the (110) cleft surfaces of the precursor mineral. Oxystibiomocrolite is the dominant phase within these corridors and corrodes and displaces stibiotantalite. Parts of the central crevice filling of the aisles consist of solid antimony. Oxystibiomicrolite is fine-grained (≤ 0.1 mm), although coarse-grained aggregates have rarely been observed.

physical and chemical properties

The extremely fine-grained nature of the oxystibiomicrolite hinders the determination of its physical properties.

Oxystibiomicrolite is greenish-white to white, while its line color is always white. The gloss on the surfaces of the translucent oxystibiomicrolite is not recognizable due to the small grain size. Oxystibiomicrolite is gray in the reflected light and significantly darker than tantalite and especially stibiotantalite. It has a very high value for light refraction (measured: n> 1.9; calculated for various compositions: 2.072 to 2.163).

Oxystibiomicrolite is not cleavable . Due to its brittleness , however , it breaks like amblygonite , with the fracture surfaces being uneven. The Mohs hardness of the mineral cannot be measured directly. Since it is softer than neighboring stibiotantalite grains, its Mohs hardness must be lower than that of stibiotantalite (5.5). The Mohs hardness of Oxistibiomikrolith is therefore <5.5. The calculated density for oxystibiomicrolite is 5.84 to 6.22 g / cm³.

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

Education and Locations

For oxystibiomicrolite, a secondary formation is assumed due to the textural relationships to its accompanying minerals as well as the geological and geochemical characteristics of the pegmatite at its type locality, whereby the mineral formed during the conversion of stibiotantalite.

Typical accompanying minerals of the oxystibiomicrolite at its type locality are stibiotantalite, native antimony, allemontite , lithiophilite , beryl , cassiterite , minerals from the system columbite (Mn) - columbite (Fe) - tantalite (Mn) - tantalite (Fe) and others Representative of the microlith group.

As a very rare mineral formation, the oxystibiomicrolite could only be described from two sources so far (as of 2018). The type locality for oxystibiomicrolite is the lithium-rich albite area of ​​the complex granite pegmatite (LCT type) "Varuträsk" near Skellefteå in the municipality of the same name, Skellefteå , province of Västerbotten County and the historic province of Västerbotten , Sweden . Another occurrence is Myoukenyama (Myokensan) in the city of Hitachi-Ōta , Ibaraki Prefecture , Kantō Region , Honshū Island , Japan .

The displacement of stibiotantalite by a microlite phase and antimony has been reported from various locations, but in most cases without chemical data. The few cases with chemical analyzes of the newly formed microlithic phase include:

  • "Odd West Pegmatite", Bernic Lake, Lac du Bonnet area, Manitoba , Canada , with the composition at the A position (Ca 0.71 Sb 0.46 Na 0.22 Fe 0.04 Sn 0 , 03 ) Σ = 1.46
  • Pegmatite "Alto do Giz", Minas Gerais , Brazil , with the composition on the A position (Ca 0.31 Sb 0.14 Pb 0.13 Mn 0.07 Bi 0.01 ) Σ = 0.68

In both cases, however, calcium dominates in the A position, so that it is not oxystibiomicrolite, but oxycalciomicrolite.

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

use

Oxystibiomicrolite is of no practical importance due to its rarity.

See also

literature

  • Lee A. Groat, Petr Černý, T. Scott Ercit: Reinstatement of stibiomicrolite as a valid species . In: Geologiska Foreningens i Stockholm Forhandlingar . tape 109 , no. 2 , 1987, pp. 105-109 , doi : 10.1080 / 11035898709453757 (English, researchgate.net [PDF; 316 kB ; accessed on August 30, 2018]).
  • Stibiomicrolite . 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 9, 2018]).

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 Lee A. Groat, Petr Černý, T. Scott Ercit: Reinstatement of stibiomicrolite as a valid species . In: Geologiska Foreningens i Stockholm Forhandlingar . tape 109 , no. 2 , 1987, pp. 105-109 , doi : 10.1080 / 11035898709453757 (English, researchgate.net [PDF; 316 kB ; accessed on August 30, 2018]).
  2. ↑ a b 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).
  3. ↑ a b c d e f g stibiomicrolite . 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 9, 2018]).
  4. ↑ a b c d Oxystibiomicrolite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 29, 2020 .
  5. ↑ Percy Quensel, Thelma Berggren: Minerals of the Varuträsk Pegmatite XI. The Niobate – Tantalate Group . In: Geologiska Föreningen i Stockholm Förhandlingar . tape 60 , no. 2 , 1938, p. 216–225 , doi : 10.1080 / 11035893809444996 (English).
  6. ^ William F. Foshag: New mineral names: stibio-microlite . In: The American Mineralogist . tape 23 , 1938, pp. 542 (English, minsocam.org [PDF; 146 kB ; accessed on September 9, 2018]).
  7. ↑ Michael Fleischer: Discredited minerals: Stibiomicrolite . In: The American Mineralogist . tape 27 , no. 6 , 1942, pp. 466 (English, minsocam.org [PDF; 126 kB ; accessed on September 9, 2018]).
  8. ^ 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]).
  9. ↑ Catalog of Type Mineral Specimens - S. (PDF 143 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed April 29, 2020 .
  10. ↑ 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]).
  11. ^ 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]).
  12. ^ 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 .
  13. ↑ Localities for Oxystibiomicrolite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 29, 2020 .
  14. ↑ List of locations for oxystibiomicrolite in the Mineralienatlas and Mindat , accessed on April 29, 2020.