Fersmanite

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Fersmanite
Fersmanite-666760.jpg
Fersmanite from Eweslogtschorr in the Chibinen , Kola Peninsula, Russia (size: 20 mm × 15 mm × 7 mm; largest crystal: 7 mm)
General and classification
chemical formula
  • Ca 4 (Na, Ca) 4 (Ti, Nb) 4 (Si 2 O 7 ) 2 O 8 F 3
  • (Ca, Na) 8 (Ti 4+ , Nb) 4 [O 8 | (F, OH) 3 | (Si 2 O 7 ) 2 ]
Mineral class
(and possibly department) 		Silicates and germanates - group silicates (sorosilicates)
System no. to Strunz
and to Dana 		9.BE.72 ( 8th edition : VIII / A'.07)
02.56.05.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 10.183 (2)  Å ; b  = 10.183 (2) Å; c  = 20.396 (4) Å
β  = 97.19 (3) °
Formula units Z  = 4
Physical Properties
Mohs hardness 5 to 5.5
Density (g / cm 3 ) measured: 3.44 to 3.46; calculated: [3.43]
Cleavage is missing
Break ; Tenacity uneven
colour dark brown to golden yellow
Line color brownish white
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.873 to 1.886
n β  = 1.914 to 1.930
n γ  = 1.914 to 1.939
Birefringence δ = 0.041 to 0.053
Optical character biaxial negative
Axis angle 2V = 0 ° to 7 ° (measured)

Fersmanite is a very rare mineral from the mineral class of " silicates and germanates " with the chemical composition Ca 4 (Na, Ca) 4 (Ti, Nb) 4 (Si 2 O 7 ) 2 O 8 F 3 . The elements sodium and calcium or titanium and niobium specified in round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components (silicate complex, oxygen and fluorine ) of the mineral. Structurally, Fersmanit belongs to the group silicates (sorosilicates).

Fersmanite crystallizes in the monoclinic crystal system , but mostly develops pseudo tetragonal , deformed crystals up to about three centimeters in diameter. The crystals are transparent to translucent and their surfaces have a glass-like sheen . The color of the mineral varies between dark brown and golden yellow. In contrast, its line color is brownish-white.

With a Mohs hardness of 5 to 5.5, Fersmanite is one of the medium-hard minerals and roughly corresponds to the hardness of the reference mineral apatite (5), which is also contained in tooth enamel .

Etymology and history

Fersmanite was first discovered on Mount Eweslogtschorr in the Chibinen on the Russian Kola Peninsula and described in 1929 by A. Labuncov, who named the mineral after the Russian mineralogist, geochemist and crystallographer Alexander Evgenjewitsch Fersman .

The type material of the mineral is in the Fersman Museum in Moscow under the catalog no. 33193/94 kept.

classification

In the outdated 8th edition of the mineral classification according to Strunz , the Fersmanite belonged to the department of "Neso-Subsilicates" (with cations in octahedral coordination (etc.)), where together with tundrite in the appendix of the " Titanit series" with the system No. VIII / A'.07 with the members Malayaite and Titanite .

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. VIII / C.16-30 . In the “Lapis system”, this corresponds to the “Group silicates” department, where Fersmanit and Belkovit form an independent but unnamed group

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies Fersmanite in the group of "group silicates". However, this is further subdivided according to the structure of the silicate groups, the possible presence of additional anions and the coordination of the cations involved , so that the mineral is classified in the sub-section “Si 2 O 7 groups with additional anions; Cations in octahedral [6] and greater coordination ”can be found, where it is the only member of the unnamed group 9.BE.72 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Fersmanite to the class of “silicates and Germanates”, but there in the more finely divided division of “group silicates: Si 2 O 7 groups and O, OH, F and H 2 O “a. Here he is as together with dovyrenite , Götzenit , Mosandrite , Nacareniobsit- (Ce) , Rinkit and Roumait in the " Mosandrite and related species " with the system no. 56.02.05 within the subsection "Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with cations in [4] and / or> [4] -coordination".

Crystal structure

Fersmanite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 10.183 (2)  Å ; b  = 10.183 (2) Å; c  = 20.396 (4) Å and β = 97.19 (3) ° and 4 formula units per unit cell . Template: room group / 15

Education and Locations

Fersmanit forms in aegirinreichen nepheline - pegmatites , where he among other things, apatite , different feldspars , Lamprophyllit , Pektolith , Rinkit and various sulfides associated occurs.

As a rare mineral formation, Fersmanite could only be detected at a few sites, with around 15 sites being documented so far (as of 2019). At its type locality Eweslogtschorr, the mineral appeared in corridors No. 1 and 2 of the Labuntsov, the 3rd tributary of the Vuonnemijok . In addition, it was found in Russia on the Kukiswumtschorr in the apatite pits there and on the Raswumtschorr in the Chibinen .

The only known site in Germany so far is the “Löhley” quarry in the Vulkaneifel district in Rhineland-Palatinate, about 800 meters northwest of the municipality of Üdersdorf . Other previously known sites are only the “Bortolan” quarry near Poços de Caldas in Brazil and a rare earth pit field in the Wet Mountains area in Custer County (Colorado) .

See also

literature

  • A. Labuncov: Ферсманит - новый минерал из Хибинских Тундр . In: Доклады Академии Наук СССР . 1929, p. 297–301 (Russian, rruff.info [PDF; 213 kB ; accessed on December 30, 2019] Title translation into French: La fersmanite - un nouveau minéral des Monts Chibines . Published by Comptes Rendus (Doklady) de l'Académie des Sciences de l'URSS ).
  • Melvin P. Machin: Fersmanite, (Ca, Na) 4 (Ti, Nb) 2 Si 2 O 11 (F, OH) 2 : a restudy . In: The Canadian Mineralogist . tape 15 , 1977, pp. 87-91 ( rruff.info [PDF; 393 kB ; accessed on December 30, 2019]).

Web links

Commons : Fersmanite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: November 2019. (PDF 1720 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, November 2019, accessed December 30, 2019 .
  2. ^ Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  582 (English).
  3. ↑ a b c d Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  4. ↑ a b c Elena Sokolova, Frank C. Hawthorne, Alexander P. Khomyakov: The crystal chemistry of fersmanite, Ca 4 (Na, Ca) 4 (Ti, Nb) 4 (Si 2 O 7 ) 2 O 8 F 3 . In: The Canadian Mineralogist . tape 40 , 2002, p. 1421–1428 (English, rruff.info [PDF; 1.7 MB ; accessed on December 30, 2019]).
  5. ↑ a b c d e f g Fersmanite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 74  kB ; accessed on December 30, 2019]).
  6. ↑ a b c d Fersmanite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 30, 2019 .
  7. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 207 .
  8. ↑ Catalog of Type Mineral Specimens - F. (PDF 73 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed December 30, 2019 .
  9. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1816 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed December 30, 2019 .
  10. ↑ Localities for Fersmanite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 30, 2019 .
  11. ↑ Find location list for Fersmanite in the Mineralienatlas and Mindat , accessed on December 30, 2019.