Leiteit

from Wikipedia, the free encyclopedia
Leiteit
Frontpage-248019.jpg
General and classification
other names

IMA 1976-026

chemical formula
  • ZnAs 2 O 4
  • ZnAs 3+ 2 O 4
  • (Zn, Fe) As 2 O 4
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.JA.05 ( 8th edition : IV / J.10)
45.01.07.01
Similar minerals plaster
Crystallographic Data
Crystal system Monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = 4.54  Å ; b  = 5.02 Å; c  = 17.60 Å
β  = 90.8 °
Formula units Z  = 4
Physical Properties
Mohs hardness 1.5 to 2
Density (g / cm 3 ) 4.3 (measured); 4.619 (calculated)
Cleavage completely after {001}; Split leaves inelastically flexible, somewhat cuttable
Break ; Tenacity not specified; not specified
colour colorless, yellowish, pale brown, reddish brown to brown
Line color not specified, well known
transparency transparent
shine Silky luster, pearlescent luster on cracked surfaces
Crystal optics
Refractive indices n α  = 1.87
n β  = 1.880
n γ  = 1.98
Birefringence δ = 0.11
Optical character biaxial positive
Axis angle 2V = 29.5 °
Other properties
Chemical behavior slow dissolution in 1: 1 dilute hydrochloric acid

Leiteit is a very rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the monoclinic crystal system with the idealized chemical composition ZnAs 2 O 4 and is thus chemically seen a zinc - arsenite , specifically a arsenite with chain structure for the [As 2 O 4 ] 2- groups are characteristic.

Leiteit rarely develops crystals that are fused in parallel and show pyramidal end faces. Much more common are easily cleavable, silky-glossy and flexible masses up to 17 cm in length, which rarely sit on a matrix and often do not have any accompanying minerals .

Etymology and history

The discoverer of the Leiteit is the Portuguese-born South African amateur mineralogist Luis Antonio Bravo Teixeira-Leite (1942–1999), who noticed the mineral among other specimens from Tsumeb in the early 1970s. Corresponding investigations led to the determination of the presence of a new mineral, which was recognized in 1976 by the International Mineralogical Association (IMA) and in 1977 by a French-American research team with Fabien P. Cesbron , Richard C. Erd , Gerald K. Czamanski and Hélène Vachey was described as Leiteit. The mineral was named after its discoverer Luis Antonio Bravo Teixeira-Leite.

Type material of the mineral is made at the University of Pierre and Marie Curie , Paris in France ; in the Natural History Museum , London in the United Kingdom (Catalog No. 1976,432); in the Royal Ontario Museum , Toronto , Canada (catalog number M34727), and in the National Museum of Natural History , Washington, DC (catalog number 137105).

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Leiteit belonged to the department of "Arsenites (with As 3+ )", where together with Manganarsit and Trippkeit he included the group of "Arsenites with chain structure [As 2 O 4 ] 2− groups "with the system no. IV / J.10 .

In contrast , the 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), classifies Leiteit in the newly defined division of "arsenites, antimonites, bismuthites, sulfites, selenites and tellurites". This is further subdivided according to the possible presence of crystal water and / or additional anions , so that the mineral is classified in the sub-section “Arsenites, Antimonides, Bismutites; without additional anions, without H 2 O ”, where it is the only member of the unnamed group 4.JA.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Leiteit, however, to the class of "phosphates, arsenates and vanadates" and there to the category of "acids and normal antimonites, arsenites and phosphites". Here he is the only member of the unnamed group 45.01.07 within the sub-section “ Acid and normal antimonites, arsenites and phosphites with various formulas ”.

Crystal structure

Leiteit crystallizes in the monoclinic crystal system in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 4.54  Å ; b  = 5.02 Å; c  = 17.60 Å and β = 90.8 ° as well as four formula units per unit cell . Template: room group / 14

The structural units of the crystal structure of the conductive side consist of an open layer of corner-linked Zn tetrahedra parallel (001) and individual arsenite chains parallel [100]. Each zinc tetrahedron layer is flanked on both sides by arsenite chains. The resulting composite layers are cross-linked by long As-O bonds. The excellent cleavage of the conductor is due to these weak As-O bonds. The structure of the Leiteits differs significantly from that of its chemical analogue Trippkeit and represents a new type of structure.

properties

morphology

In Tsumeb Leiteit formed rarely crystals, but often only characteristic gypsum-like ( marienglas-like ), easily fissile aggregates and flexible masses up to 17 cm in length, which rarely sit on a matrix and often do not have any accompanying minerals . The first guide sides found in Tsumeb consisted of split pieces without terminations. From the "Zinc Pocket" opened in 1992 almost isometric crystals up to 4 cm in size terminated on both sides with sharp-edged end surfaces were recovered; In addition, long prismatic crystals up to 5 cm in size, also with end faces on both sides, came to light. In a third cavity, up to 17 × 5 × 5 cm in size, prismatic and striped Leiteit crystals with terminations at both crystal ends, embedded in a red clay, were found. All these crystals from the third pocket are said to have been polished due to the transparency.

physical and chemical properties

The crystals of the Leiteit are colorless, yellowish, pale brown, reddish brown to brown. The line color of the mineral is not specified in the original publication, but it should be white to slightly brown depending on the color. The surfaces of the transparent crystals have a silky sheen , while the cracked surfaces have a pearly sheen .

The mineral is perfectly cleavable according to {001}, whereby the split leaves are inelastic, flexible and even somewhat cuttable. With a Mohs hardness of 1.5 to 2, Leiteit is one of the soft minerals that are slightly easier to scratch with the fingernail than the reference mineral gypsum . The calculated density of the mineral is 4.619 g / cm³.

Leiteit slowly dissolves in 1: 1 dilute hydrochloric acid .

Modifications and varieties

Leiteit is the zinc-dominant analogue to the copper-dominated trippidity, Cu [As 2 O 4 ], without being isotypic (isostructural) to it.

Education and Locations

Pearl-white conductivity from the Tsumeb mine accompanied by orange-red ludlockite (step size: 2.8 × 1.8 × 1.2 cm)

So far (as of 2016) the mineral could only be reliably detected at its type locality , the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit "Tsumeb Mine" (Tsumcorp Mine) near Tsumeb in the Namibian region of Oshikoto .

Leiteit is a typical secondary mineral and formed at low temperatures in the oxidation zone of the hydrothermal polymetallic ore deposit Tsumeb, which is located in dolomite stones , together with other zinc- and arsenic-containing minerals. Due to the increased occurrence of arsenite minerals on the 44th and 45th levels, it can be assumed that at the time these minerals were formed, a reducing atmosphere, lacking in oxygen , must have prevailed here.

Even though there are many leading elements in the collections monominerally and without a matrix, there are characteristic associations, particularly beautiful, especially with red ludlockite and light green reinerite . Leiteit can be found in the primary ore minerals chalcosine , tennantite and germanite and, in addition to the above-mentioned secondary minerals, can also be accompanied by Schneiderhöhnite , zinc-bearing stottite , zinc croselite , tsumcorite , stranskiite , legrandite and smithsonite .

Spectacular Leiteit crystals came from the 10 cm diameter "Zinc Pocket" found on the 44th floor in Tsumeb in 1992, accompanied by a colorful suite of paragenesis minerals. The sequence of precipitation was (from the oldest to the youngest mineral) silky white conductivity → sea green reinerite → orange legrandite → white adamin → ivory colored paradamine → pink smithsonite. The 45th level also provided numerous levels, so that the mineral began to be regarded as common. The accompanying minerals of the Leiteits in the third important pocket in Tsumeb were needle-like, white Adamin, small blue spherical Köttigit aggregates as well as a new blue K-Cu-Zn-Fe-As mineral ("Mineral GS4"), which is not yet complete is identified.

At three other sites it was initially believed to have discovered Leiteit. However, more recent analyzes have largely refuted these discoveries.

The find published in 1992 by K. Schebesta on the slag heaps near Walchen near Öblarn in the Austrian state of Styria was identified as valentinite in 2013 after a second analysis by Uwe Kolitsch (* 1966) .

In 1988 Günter Schnorrer-Köhler announced an unspecified slag discovery site in the Harz Mountains in Lower Saxony and in 1989 the Caspari smelter near the Caspari colliery in Uentrop (Arnsberger Wald, Sauerland) in North Rhine-Westphalia as new sites for Leiteit. The finds from the Caspari smelter have been considered dubious since 1993, after new analyzes by G. Blaß and HW Graf, since all the alleged guide finds were identified as valentinite.

A site in France, more precisely the “Le Bocard” slag discovery site at the Vialas smelter not far from the village of the same name in the Lozère department, is also in doubt. After a comparison of photos of analyzed Valentinite from other slag locations with those from the smelter Vialas it is assumed that this could also be Valentinite. However, this assumption has not yet been confirmed (as of 2017).

use

As a raw material

With a ZnO content of 28.5%, Leiteit would be a zinc ore, but it is far too rare for that and also much more interesting for mineral collectors.

As a gem

The entire contents of a pocket from the Tsumeb mine with particularly beautiful and large, completely transparent Leiteit crystals has been polished.

See also

literature

  • Fabien P. Cesbron, Richard C. Erd, Gerald K. Czamanski, Hélène Vachey: Front page: a new mineral from Tsumeb. In: Mineralogical Record. Volume 8, 1977, pp. 8, 95-97.
  • Leiteit. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001. ( PDF, 70 kB )

Web links

Commons : Home page  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e 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.  263 .
  2. ↑ a b c d e f Leiteite . 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 ]).
  3. ↑ a b c d e f g h i j k l m n Fabien P. Cesbron, Richard C. Erd, Gerald K. Czamanski, Hélène Vachey: Front page: a new mineral from Tsumeb . In: Mineralogical Record . tape 8 , 1977, pp. 95-97 .
  4. ↑ a b Subrata Ghose, PK Sen Gupta, EO Schlemper: Leiteite, ZnAs2O4: a novel type of tetrahedral layer structure with arsenite chains . In: American Mineralogist . tape 72 , 1987, pp. 629-632 ( rruff.info [PDF; 407 kB ]).
  5. ↑ a b c Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 276 and 167 .
  6. ↑ Find location list for Leiteit in the Mineralienatlas and Mindat
  7. ↑ Mindat - Unnamed Mineral (Tsumeb GS4)
  8. ↑ K. Schebesta: Slag minerals from the Walchen near Öblarn . In: Lapis mineral magazine . tape 17 , no. 2 , 1992, ISSN  0176-1285 , pp. 19-30, 50 .
  9. ↑ U. Kolitsch: Plumbojarosit, Wroewolfeit and the phase Ca [Zn 8 (SO 4 ) 2 (OH) 12 C 12 ] (H 2 O) 9 from the slag of the Walchen near Öblarn, Niedere Tauern, Styria . In: New mineral finds from Austria LXII. Carinthia II . tape 203/123 , 2013, p. 133-134 ( PDF on ZOBODAT [accessed July 8, 2017]).
  10. ^ Günter Schnorrer-Köhler: Mineralogical Notes IV . In: Association of Friends of Mineralogy and Geology (VFMG) e. V. (Ed.): The opening . tape 39 . Heidelberg 1988, p. 153-168 .
  11. ↑ Günter Schnorrer-Köhler: The antimony ore deposits of the Caspari colliery near Arnsberg in the Sauerland . In: Lapis mineral magazine . tape 14 , no. 6 , 1989, pp. 11-32, 50 .
  12. ↑ G. Blaß, HW Graf: New Finds . In: Mineral World . tape 4 , no. 2 , 1993, p. 57-60 .
  13. ↑ Mindat - Leiteite from Vialas smelter slag locality, Vialas, Pont-de-Montvert, Lozère, Occitanie, France