Oxystannomicrolite

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Oxystannomicrolite
Stokesite-Stannomicrolite-Albite-206836.jpg
Oxystannomicrolite ("stannomicrolite") on stokesite and albite from the pegmatite Córrego do Urucum near Galiléia, Doce Valley, Minas Gerais, Brazil (step size: 4.1 cm × 3.3 cm × 3.0 cm)
General and classification
other names
  • Stannomicrolite
  • Sukulaite
chemical formula Sn 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)
02/08/02/06 (stannomicrolite)
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  = 10.57  Å
Formula units Z  = 8
Physical Properties
Mohs hardness > 6 to 7 (polishing hardness is greater than that of cassiterite)
Density (g / cm 3 ) 8.34 (measured on synthetic Sn 2 Ta 2 O 7 ); 8.21 (calculated for synthetic Sn 2 Ta 2 O 7 )
Cleavage not specified
Break ; Tenacity uneven; brittle
colour yellowish brown; light gray in reflected light with a reddish or purple tinge
Line color no information, probably light brown
transparency translucent
shine not specified
Crystal optics
Refractive index n  = not defined
Optical character isotropic

Oxystannomicrolite is a very rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition Sn 2 Ta 2 O 6 O, that is a tin - tantalate with additional oxygen ions .

Oxystannomicrolite occurs at its type locality in the form of a maximum of 20 μm seams around ferro-odginite crystals. These ferro odginite crystals are in turn found as inclusions in tantalum-containing cassiterite and, if sufficiently small, can be completely displaced by oxystannomicrolite.

The type locality of the oxystannomicrolite is an unspecified, Nb-Ta-Sn-rich pegmatite ( coordinates of the pegmatite Sukula ) near the village Sukula, 10 km southwest of Tammela in the municipality of the same name, pegmatite province Tammela-Somero, landscape Kanta-Häme , historical landscape Häme , Finland .

Etymology and history

In the mid-1960s, Atso Vorma and Jaakko Siivola investigated “Ainalite” steps from Sukula near Tammela in the pegmatite province of Tammela-Somero in southwestern Finland. "Ainalite" is a tantalum-containing cassiterite variety described by Adolf Erik Nordenskiöld in 1863 . Although no exact location was given on the historical material, which was over 100 years old at the time of the investigation, it is very likely that these steps come from a granite quarry near the Makitulokas farm, which Nordenskiöld mentioned as the location where he made his "ainalite" -Gathered levels. A mineral was found in the tantalum-rich cassiterites which, after determining the physical, chemical and X-ray diffractometric properties, turned out to be a new representative of the pyrochlore group of that time. The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in May 1967. The first scientific description of this mineral as sukulaite ( English Sukulaite ) took place in 1967 by the two Finnish mineralogists Atso Vorma and Jaakko Siivola in the Finnish scientific magazine Bulletin de la Commission Géologique de Finlande . The authors named the new mineral after its place of discovery, the village of Sukula.

The type material for sukulaite is kept under catalog numbers 439, 440, 443, 444, 445 and 446 (detailed description in Vorma & Siivola 1967) in the collection of the Department of Geology and Mineralogy at the University of Helsinki .

In 1977 Donald David Hogarth discarded the name “Sukulaite” in the first “Classification and nomenclature of the pyrochlore group” (1977) in favor of “stannomicrolite” in order to underline the fact that the mineral belongs to the microlithic subgroup of the pyrochlore group. The choice was made on the basis of the chemical composition of tin ( Latin stannum ) and the crystal-chemical relationship with the representatives of the microlith group.

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 stannomicrolite, that this mineral with an A position dominated by tin in the crystal lattice, a B position dominated by Ta and by O dominated Y position with the new, nomenclature-compliant name Oxystannomikrolith ( English Oxystannomicrolite ) is to be designated. The type material of sukulaite defined by Vorma & Siivola in 1967 is now considered a type material (holotype) for oxystannomicrolite. The designation “stannomicrolite” has been discredited.

classification

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

In the now obsolete, but still partially common 8th edition of the mineral classification by Strunz part of the 2010 redefined to Oxystannomikrolith Stannomikrolith in the mineral class of "oxides and hydroxides" and then to the general division of the "oxides ratio of metal: oxygen = 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 , Stibiomikrolith (2010 redefined to Oxystibiomikrolith) and Uranmikrolith the" pyrochlore Group, microlith subgroup "with the system no. 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 oxystannomicrolite (formerly stannomicrolite ) 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. Oxystannomicrolite can be found in the together with fluorocalciomicrolite, fluorine atromicrolite, hydrokenomicrolite, hydromicrolite, hydroxykenomicrolite (formerly Cesstibtantit ), kenoplumbomicrolite, oxycalciomicrolite and oxystibiomicrolite (formerly stibiomicrolite ).

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the oxystannomicrolite (formerly stannomicrolite ) to the class of "oxides and hydroxides", but there in the department of "multiple oxides with Nb, Ta and Ti". Here it is together with microlite, bariomicrolite, fluorine atromicrolite, plumbomicrolite, uranium microlite, bismuthomicrolite and stibiomicrolite 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 chemical analysis of the “Sukulaite” from the type publication determined with the microprobe yielded 47% Ta 2 O 5 ; 8% Nb 2 O 5 ; 1% TiO 2 ; 2% MnO; 1.7% FeO and 40% SnO 2 , from which the simplified formula (Ta, Nb) 2 Sn 2 O 7 was determined. T. Scott Ercit and colleagues re-examined the "sukulaite", which has now been renamed "stannomicrolite". According to their microprobe analyzes, pewter is partly bivalent and partly tetravalent and sits in different positions. They found 41.86% Ta 2 O 5 ; 7.40% Nb 2 O 5 ; 0.99% TiO 2 ; 1.42% MnO; 2.09% FeO; 8.49% SnO 2 ; 35.63% SnO and 0.61% H 2 O (calculated from the stoichiometry). This resulted in the empirical formula (Sn 2+ 1.69 Fe 2+ 0.18 Mn 2+ 0.13 ) Σ = 2.00 (Ta 1.21 Sn 4+ 0.36 Nb 0.35 Ti 0.08 ) Σ = 2.00 [O 6.57 (OH) 0.43 ] Σ = 7.00 determined, which leads to (Sn 2+ , Fe 2+ , Mn 2+ ) (Ta, Sn 4+ , Nb) 2 ( O, OH) 7 has been simplified.

The official formula of the IMA is Sn 2 Ta 2 O 6 O. Of all the minerals, only thoreaulite, (Sn 2+ , Pb) (Ta, Nb) 2 O 6 , has chemical similarities to oxystannomicrolite.

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

Crystal structure

Crystal structure of oxystannomicrolite as a "ball-and-stick model". Color legend: tantalum: yellow-brown; Tin: purple; Oxygen: red.

Oxystannomicrolite crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.57  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 oxystannomicrolite 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 the direction of <110>, which take up the oxygen atoms and the atoms in the A position such as Sn.

Oxystannomicrolite is isotypic (isostructural) to other representatives of the pyrochlore upper group which crystallize in the space group Fd 3 m (space group no. 227) . Template: room group / 227

properties

morphology

Oxystannomicrolite forms at its type locality a maximum of 20 μm thick margins around 0.01 to 0.2 mm large, occasionally strip-shaped ferro-odginite crystals, whereby the ferro-odginite crystals "swim" in the form of inclusions in tantalum-containing cassiterite. If they are sufficiently small, they may have been completely displaced by oxystannomicrolite. Oxystannomicrolite itself forms aggregates about 5 µm in size.

physical and chemical properties

Due to the extremely fine-grained nature of the oxystannomicrolite, a number of its physical properties cannot be determined.

Oxystannomicrolite is yellowish brown, its line color is probably light brown. The gloss on the surfaces of the translucent oxystannomicrolite is not recognizable due to the small grain size. Oxystannomicrolite is light gray in reflected light with a reddish or purple tinge; its color is lighter than that of cassiterite and ferroodginite. In crossed polars , oxystannomicrolite has strong reddish-brown internal reflections due to the small grain size, which is why it is not possible to decide whether the mineral is optically isotropic or not.

There is no information on a possible cleavage of the oxystannomicrolite. 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. But since it is considerably harder than neighboring cassiterite grains, its Mohs hardness must be significantly higher than that of cassiterite (6 to 7). The Mohs hardness of oxystannomicrolite is> 6. The density for oxystannomicrolite could neither be determined experimentally nor calculated. Synthetic Sn 2 Ta 2 O 7 ) has a measured density of 8.34 g / cm³ and a calculated density of 8.21 g / cm³.

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

Education and Locations

“Stannomicrolite” on stokesite. Excerpt from the picture in the info box.
Yellowish brown “stannomicrolite” on stokesite. Córrego do Urucum, Minas Gerais, Brazil (step size: 1.2 cm × 1.1 cm × 0.9 cm).

For oxystannomicrolite, 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 displacement of stannomicrolite.

Typical accompanying minerals of the oxystannomicrolite at its type locality are ferro-odginite and solid bismuth, all of which only occur in the form of tiny inclusions in tantalum-containing cassiterite. The tantalum-containing cassiterite in turn only forms growth zones around lighter, tantalum-free cassiterite cores. The cassiterites are usually only 1 mm in size, but can reach sizes of several centimeters.

As a very rare mineral formation, the oxystannomicrolite could so far (as of 2018) only be described from one source. The type locality for oxystannomicrolite is an unnamed Nb-Ta-Sn-rich granite pegmatite in the pegmatite province of "Tammela-Somero" in the village of Sukula - and possibly near the Makitulokas farm. The site is located 10 km southwest of Tammela in the same community, landscape Kanta-Häme , historical region Häme , Finland .

The “stannomicrolite” described by Pavel Uher and colleagues is a Ca- or zero-valent dominant representative of the microlithic group.

Furthermore, tiny yellow crystals on spherical stokesite from the pegmatite "Córrego do Urucum" near Galiléia in the river valley of the Rio Doce , Minas Gerais , Brazil , were described as "stannomicrolite" in the sense of Donald David Hogarth's definition. Only one such “stannomicrolite” was confirmed by a chemical analysis as “stannomicrolite” and thus as oxystannomicrolite - all other so-called minerals are “ either normal microlite or uranium microlite ”.

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

use

Oxystannomicrolite is of no practical importance due to its rarity.

See also

literature

  • Atso Vorma, Jaakko Siivola: Sukulaite - Ta 2 Sn 2 O 7 - and wodginite as inclusions in cassiterite in the granite pegmatite in Sukula, Tammela in SW Finland . In: Bulletin de la Commission Géologique de Finlande . No. 229 , 1967, pp. 173-187 (English).
  • Stannomicrolite . 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 12, 2018]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 520 (first edition: 1891, as sukulaite).
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 403 (as sukulaite).

Web links

Commons : Oxystannomicrolite  - 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 Atso Vorma, Jaakko Siivola: Sukulaite - Ta 2 Sn 2 O 7 - and wodginite as inclusions in cassiterite in the granite pegmatite in Sukula, Tammela in SW Finland . In: Bulletin de la Commission Géologique de Finlande . No. 229 , 1967, pp. 173-187 (English).
  2. ↑ a b c d e f g h Stannomicrolite . 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 12, 2018]).
  3. ↑ Eero Mäkinen: The granite pegmatites of Tammela in Finland and their minerals . In: Bulletin de la Commission Géologique de Finlande . No. 35 , 1913, pp. 1-101 .
  4. ^ Adolf Erik Nordenskiöld : Om tantalitartade mineralier från nejden af ​​Torro . In: Öfversigt af Kongl. Vetenskaps-akademiens förhandlingar . tape  20 , 1863, p. 443–453 (Swedish, limited preview in Google Book search).
  5. ↑ Adolf Erik Nordenskiöld : About tantalite-like minerals from the area of ​​Torro . In: Poggendorfs annals of physics and chemistry . tape  122 , 1864, p. 604–615 ( limited preview in Google Book search).
  6. ^ A b c d 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]).
  7. ↑ a b c d e 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]).
  8. ^ A b c Andrew G. Christy, Daniel Atencio: Clarification of 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]).
  9. ↑ T. Scott Ercit, Petr Černý, Jaakko Siivola: The composition of stannomicrolite . In: New yearbook for mineralogy, monthly books . tape 1987 , no. 6 , 1987, pp. 249–252 (English, researchgate.net [PDF; 115 kB ; accessed on September 12, 2018]).
  10. ^ IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB)
  11. ↑ a b Mindat - Oxystannomicrolite , accessed on September 12, 2018 (English)
  12. ↑ 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).
  13. ^ 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]).
  14. ^ 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 .
  15. ↑ Webmineral - Stannomicrolite (Oxystannomicrolite) , accessed on September 12, 2018 (English)
  16. ↑ Madeleine Gasperin: Synthèse et identification de deux oxydes doubles de tantale et d'etain . In: Comptes Rendus Acad. Sci. Paris . tape 240 , no. 24 , 1955, pp. 2340-2342 (French).
  17. ↑ Mindat - Number of sites for Oxystannomikrolith , accessed on September 12, 2018 (English)
  18. ↑ List of locations for oxystannomicrolite in the Mineralienatlas and Mindat (accessed on September 12, 2018)
  19. ↑ Pavel Uher, Petr Černý, Ron Chapman: Foordite-thoreaulite, Sn 2+ Nb 2 O 6 –Sn 2+ Ta 2 O 6 : compositional variations and alteration products . In: European Journal of Mineralogy . tape 20 , no. 4 , 2008, p. 501-516 , doi : 10.1127 / 0935-1221 / 2008 / 0020-1845 (English).
  20. ↑ a b Mindat - locality pegmatite "Córrego do Urucum" , accessed on September 12, 2018 (English)