Zinnwaldite

from Wikipedia, the free encyclopedia
Crystal group with zinnwaldite flakes from the type locality Zinnwald in the Ore Mountains
Rough handpiece made of yellowish zinnwaldite - exhibited in the Mineralogical Museum of the University of Bonn
Crystal specimen with greenish zinnwaldite (right), white albite and smoky quartz (left) from Sawtooth Batholith / Sawtooth Mts, Custer County (Idaho) , USA (size 2.5 cm × 1.7 cm)

Zinnwaldite , also known as lithium iron mica (outdated also lithion iron mica ), is a mixed crystal made from the minerals siderophyllite and polylithionite (and therefore not a separate type of mineral ) with the chemical formula K (Fe 2+ , Al, Li, □) 3 [(OH , F) 2 | (Si, Al) 4 O 10 ]. The cations iron , aluminum and lithium and the anions fluorine and hydroxide ions or silicon and aluminum indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the formula.

In addition, zinnwaldite is recognized as a group name by the International Mineralogical Association (IMA) and belongs together with its end members

  • Siderophyllite - K (Fe 2+ , Al) 3 [(F, OH) 2 | (Si, Al) 4 O 10 ] or KFe 2+ 2 Al (Si 2 Al 2 ) O 10 (OH) 2
  • Polylithionite - KLi 2 Al [F 2 | Si 4 O 10 ] or KLi 2 Al (Si 4 O 10 ) F 2

to the "Phlogopitgruppe" with the system no. 9.EC.20 , which belongs to the division of layered silicates (phyllosilicates) in the systematics of minerals according to Strunz (9th edition) . According to M. Rieder et al., The end links of the mixed series belong to the group of real mica .

Like the end links of the seamless mixed series of siderophyllite – polylithionite, the zinnwaldites also crystallize in the monoclinic crystal system . They usually develop fine to coarse-leaved crystals that are hexagonal due to the formation of twins or are found in the form of scaly or fan-shaped to rosette-shaped mineral aggregates with a glass-like sheen on the surfaces. Depending on the composition of the mixed crystals, these take on a gray-brown to yellow-brown or light purple to dark green color. Very rare black zinnwaldites are also known as "raven mica".

Etymology and history

Zinnwaldite was first described in 1845 by Wilhelm von Haidinger , who named the mineral after its type locality (first place of discovery) in the Zinnwald area ( Cínovec or Zinnwald-Georgenfeld ) in the Ore Mountains between Saxony and Bohemia .

Postage stamp "Zinnwaldit, Zinnwald / Erzg."

Together with smoky quartz, zinnwaldite was one of the motifs selected for a series of GDR stamps on minerals from the Freiberg Mining Academy issued on February 22, 1972 .

properties

The Mohs hardness of zinnwaldite varies between 2.5 and 4, depending on its composition. Its (measured) density is between 2.90 and 3.02 g / cm³.

Like all mica, its cleavability is very perfect, that is, the finest flakes can be cleaved from the crystal perpendicular to the c-axis, whereby these flakes are flexible and elastically deformable due to their toughness ( tenacity ).

Zinnwaldite samples are sensitive to acids and easily melt into a dark pearl before the soldering tube , coloring the flame red.

Education and Locations

Zinnwaldite, like the related mica lepidolite, is formed under pegmatitic - pneumatolytic conditions and is mostly found in association with fluorite , cassiterite , quartz , scheelite , topaz and wolframite , but also lepidolite, spodumene , beryl , tourmaline group , mainly in old men (rarely also in Granites ). Zinnwaldite changes into a kaolin-like product through weathering .

As a rather rare mineral formation, zinnwaldite can sometimes be abundant at various sites, but overall it is not very common. So far (as of 2016) around 260 sites are known.

At its type locality Cínovec in the Czech Republic, particularly rich aggregates with tin forest scales of up to 10 cm in diameter were found. Even larger crystals with a diameter of up to 15 cm were discovered in the pegmatites near Virgem da Lapa in the Brazilian state of Minas Gerais . Well-known deposits in addition to tin forest are Cornwall in England, Bolivia , Malaysia and northern Portugal .

Other sites are found in Egypt, Algeria, Argentina, Australia, Brazil, China, Finland, France, Greenland, Italy, Japan, Canada, Korea, Madagascar, Mongolia, Myanmar ( Burma ), Namibia, Norway, Peru, Poland, Rwanda, Russia, Saudi Arabia, Zimbabwe, Slovakia, Spain, South Africa, Tajikistan, Ukraine, Northern Ireland and Scotland in the United Kingdom, as well as Alaska, Colorado, California, Maine, Wisconsin and other states in the United States.

use

Depending on its composition, zinnwaldite contains between 3 and 4.5% lithium oxide and is therefore used as a raw material for lithium, which was first obtained on a technical scale in 1925 by fused-salt electrolysis .

For further use see Lithium # use .

literature

  • Wilhelm Haidinger: Handbook of determining mineralogy: containing the terminology, systematics, nomenclature and characteristics of the natural history of the mineral kingdom 2nd edition. Braumüller & Seidel, Vienna 1845. ( limited preview in Google book search)
  • Milan Rieder, Giancarlo Cavazzini, Yurii S. D'Yakonov, Viktor A. Frank-Kamenetskii, Glauco Gottardt, Stephen Guggenheim, Pavel V. Koval, Georg Müller, Ana MR Neiva, Edward W. Radoslovich, Jean-Louis Robert, Francesco P Sassi, Hiroshi Takeda, Zdeněk Weiss, David R. Wones: Nomenclature of the micas. In: The Canadian Mineralogist. Volume 36, 1998, pp. 905–912 ( PDF 573.9 kB )

Web links

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

Individual evidence

  1. ^ A b c d Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin / New York 1981, ISBN 3-11-006823-0 , p. 823 .
  2. ^ Egon Wiberg: Textbook of Chemistry . 30th and 31st edition. first part: inorganic chemistry . de Gruyter, Berlin 1952, p. 366 ( limited preview in Google Book search).
  3. ↑ Mindat - Zinnwaldite
  4. ^ A b 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.  668 .
  5. ^ IMA List of Mineral Names; 2009 (PDF 1.8 MB, p. 314).
  6. ^ 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.  667 .
  7. ↑ a b IMA List of Mineral Names; November 2015 (PDF 1.6 MB, pp. 144 and 164).
  8. ↑ a b c Zinnwaldite. 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 76.8 kB).
  9. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  749 (first edition: 1891).
  10. ↑ 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.  552 .
  11. ↑ Mindat - Number of localities for Zinnwaldite
  12. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Dörfler Verlag, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 253 .
  13. ↑ List of locations for zinnwaldites in the Mineralienatlas and Mindat