Spectacle

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Spectacle
Schaurteite.jpg
Needle-like, white Schaurteit crystals from the Tsumeb Mine, Otavi Highlands, Namibia
General and classification
chemical formula
  • Ca 3 Ge 4+ [(OH) 6 | (SO 4 ) 2 ] • 3H 2 O
  • Ca 3 Ge 4+ (SO 4 ) 2 (OH) 6 • 3H 2 O
  • Ca 3 Ge (SO 4 ) 2 (OH) 6 (H 2 O) 3
Mineral class
(and possibly department) 		Sulphates (selenates, tellurates, chromates, molybdates, tungstates)
System no. to Strunz
and to Dana 		7.DF.25 ( 8th edition : VI / D.06)
07/31/06/02
Similar minerals Butcherite
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-dipyramidal; 6 / m  2 / m  2 / m
Space group P 6 3 / mmc (No. 194)Template: room group / 194
Lattice parameters a  = 8.5253  Å ; c  = 10.8039 Å
Formula units Z  = 2
Physical Properties
Mohs hardness not determinable, 2.5
Density (g / cm 3 ) 2.65 (measured); 2.64 (calculated)
Cleavage no
Break ; Tenacity not specified; very brittle
colour colorless, white
Line color well knows
transparency semi-transparent
shine Silky gloss
Crystal optics
Refractive indices n ω  = 1.569
n ε  = 1.581
Birefringence δ = 0.012
Optical character uniaxial positive
Other properties
Special features inconsistent under the electron beam

Schaurteit is a very seldom occurring mineral from the mineral class of "sulfates (selenates, tellurates, chromates, molybdates and tungstates)" with the chemical composition Ca 3 Ge 4+ [(OH) 6 | (SO 4 ) 2 ] · 3H 2 O , and thus, from a chemical point of view, a water-containing calcium - germanium - sulfate with additional hydroxide ions .

Schaurteit crystallizes in the hexagonal crystal system and develops needle-like crystals up to one centimeter in length, which typically come together to form macroscopically silky-white, fine-fiber mineral aggregates . The mineral sits on a carbonate crust in solution cavities of the germanium-rich primary ore of the Tsumeb deposit, through whose alteration it was also formed.

Etymology and history

The mineral was discovered in 1965 by the chief geologist of the Tsumeb mine, Gerhard Söhnge , who recognized it as a new mineral and, as a result of his good contacts, passed the material on to the Institute for Mineralogy at the Technical University of Berlin. After extensive analyzes, Professor Hugo Strunz and Professor Christel Tennyson were able to present the mineral to the IMA, which recognized it as a new mineral without disagreement.

As early as 1967, Strunz and Tennyson published the first description of the show in the commemorative publication for the 50th anniversary of the German chemist and South African industrialist Werner T. Schaurte (1893–1978), a "friend and generous patron of mineralogy", to whom they also honor it named as "Schaurteit". The name Schaurteit appeared earlier in the literature, in an earlier edition of Hugo Strunz's mineralogical tables.

The type material of the mineral (holotype) was originally kept at the Technical University of Berlin , where it has been lost. Other parts of the type material at the national École supérieure des Mines de Paris , France (Cotyp), and the Smithsonian Institution belonging to National Museum of Natural History , Washington, DC (catalog no. 144520) was preserved.

classification

Already in the now outdated 8th edition of the mineral classification according to Strunz , the show belonged to the mineral class of "sulfates, chromates, molybdates and wolframates" and there to the section "anhydrous sulfates, with foreign anions ", where together with despujolsite and fleischerite it belonged to the "show Series "with the system no. VI / D.06 .

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 classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VI / D.11-20 . Also in the "Lapis Classification" this corresponds (medium-sized and very large cations) of the Department of "Anhydrous sulfates with foreign anions" where Schaurteit with Despujolsit, Genplesit , Fleischerit and Mallestigit forms an independent but unnamed group.

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also assigns the Schaurteit to the category of "Sulphates (selenates, etc.) with additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With large and medium-sized cations”, where together with despujolsite, fleischerite and mallestigite it forms the “fleischerite group” with the system -No. 7.DF.25 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Schauteit to the class of “sulfates, chromates and molybdates” and there to the “hydrated sulfates with hydroxyl or halogen” category. Here it is together with despujolsite, fleischerite and mallestigite in the " despujolsite group " with the system no. 07/31/06 within the subdivision of "Water-containing sulphates with hydroxyl or halogen with (A + B 2+ ) 2 (XO 4 ) Z q  • x (H 2 O)".

Chemism

Mean values ​​from 13 analyzes on Schaurteit from Tsumeb resulted in contents of 17.97% GeO 2 , 30.41% CaO and 29.22% SO 3 . Normalized to 17 oxygen atoms per formula (with 6 mol H 2 O per formula unit) the combined empirical and structural chemical formula is Ca 3.01 Ge 0.95 (S 2.03 O8) (OH) 6 · 3H 2 O, which leads to Ca 3 Ge (SO 4 ) 2 (OH) 6 · 3H 2 O can be idealized and requires 29.60% SO 3 , 31.09% CaO, 19.33% GeO 2, and 19.98% H 2 O.

Schaurteit is the calcium-dominant analogue of the lead- dominated fleischerite , Pb 3 Ge (SO 4 ) 2 (OH) 6 · 3H 2 O, and the Ge-dominant analogue of the Mn-dominated despujolsite, Ca 3 Mn (SO 4 ) 2 (OH) 6 3H 2 O or to the Sn-dominated genplesite , Ca 3 Sn (SO 4 ) 2 (OH) 6 3H 2 O. Although Schaurteit and Fleischerite both occur in the Tsumeb deposit, there is no solid solution formation ( substitution between Pb and Ca) known for these minerals.

Crystal structure

Schaurteit crystallizes hexagonally in the space group P 6 3 / mmc (space group no. 194) with the lattice parameters a  = 8.5253  Å and c  = 10.8039 Å as well as two formula units per unit cell . Template: room group / 194

The crystal structure of Schaurteit consists of plates of Ca (OH) 4 O 2 (H 2 O) 2 - polyhedra , which are interlocked with a mixed layer of Ge (OH) 6 - octahedra and SO 4 - tetrahedra . There are two hydrogen atoms in the asymmetric unit. H1 is connected to the Ge coordinating O3 atom and H2 to the O4 atom, creating an H 2 O molecule . Both K atoms form hydrogen bonds , O3 – H1 ··· O2 and O4 – H2 ··· O1, similar to the structure described for despujolite.

properties

morphology

Schaurteit forms long-prismatic, fibrous to needle-like crystals with a hexagonal cross-section, which come together to form divergent-rayed to tangled-rayed aggregates of occasionally even bent fibers. Originally, the maximum length of the "very thin" Schaurteit crystals was given as 0.2 mm. In the years from 1986 to 1988, however, crystals up to 1 cm in length were known to form "table tennis ball-sized" aggregates up to 5 cm in diameter.

physical and chemical properties

The color of the display crystals is colorless, water-clear to white, while their line color is always white. The surfaces of the semi-transparent crystals have a strong silky sheen , which corresponds well with the birefringence of the mineral (0.012).

No cleavage was found in the crystals on the display side, and there is no information on the breakage . The mineral, described as very brittle, has a Mohs hardness of 2.5 and is therefore one of the soft minerals that can be scratched with a copper coin a little easier than the reference mineral calcite . The measured density for Schauteit is 2.65 g / cm³, the calculated density for the mineral is 2.64 g / cm³. Under the electron beam, the mineral is as unstable as despujolsite.

Education and Locations

Schaurteit arises as a typical secondary formation in the ores of a complex, germanium-rich deposit . Germanium comes from the decomposition of former sulfidic ore minerals such as germanite . In the first discovery, the mineral sits on a millimeter-thick crystalline crust of a rhombohedral carbonate , which lines the leaching cavities in the germanite-rich primary ore. The later finds from the mid-late 1980s produced numerous highly attractive Schauteit specimens because of the color contrast between the white and black ore matrix. Apart from kegelite , no other accompanying minerals are known.

As a very rare mineral formation, Schaurteit could only be described from one point of discovery so far (as of 2016). The type locality of the Schaurteits is the second oxidation zone of the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia .

use

Due to its rarity, Schaurteit is a mineral that is highly sought after by mineral collectors.

See also

literature

  • Show page . 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; 63 kB ; accessed on December 3, 2018]).
  • Hugo Strunz, Christel Tennyson: Schaurteit, a new germanium mineral from Tsumeb / SW-Africa and its paragenesis (Festschrift Dr. Werner T. Schaurte) . 1st edition. Bauer & Schaurte, Neuss-Rhein 1967, p. 33-47 .

Web links

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

Individual evidence

  1. ^ 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.  408 (English).
  2. ↑ a b c front page . 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; 63  kB ; accessed on December 3, 2018]).
  3. ↑ a b c d e f Marcus J. Origlieri, Robert T. Downs: Schaurteite, Ca 3 Ge (SO 4 ) 2 (OH) 6 · 3H 2 O . In: Acta Crystallographica . E69, 2013, p. i6 and sup-1 to sup-7 , doi : 10.1107 / S1600536812050945 ( rruff.info [PDF; 681 kB ; accessed on May 12, 2019]).
  4. ↑ a b c d e f Hugo Strunz, Christel Tennyson: Schaurteit, a new germanium mineral from Tsumeb / SW Africa and its paragenesis (Festschrift Dr. Werner T. Schaurte) . 1st edition. Bauer & Schaurte, Neuss-Rhein 1967, p. 33-47 .
  5. ↑ a b front page. In: mindat.org. Hudson Institute of Mineralogy, accessed May 12, 2019 .
  6. ^ A b Georg Gebhard: Tsumeb: A Unique Mineral Locality . 1st edition. GG Publishing, Grossenseifen 1999, ISBN 978-3-925322-03-7 , pp. 276, 322 (English).
  7. ^ Hugo Strunz : Mineralogical tables . a classification of minerals on a crystal chemical basis; with an introduction to crystal chemistry. 4th, completely revised and enlarged edition. Academic publishing company Geest & Portig, Leipzig 1966.
  8. ↑ Catalog of Type Mineral Specimens - show page. (PDF 142 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed May 12, 2019 .
  9. ↑ 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 .
  10. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed May 12, 2019 .
  11. ↑ Madison C. Barkley, Hexiong Yang, Stanley H. Evans, Robert T. Downs, J. Marcus Origlieri: Redetermination of despujolsite, Ca 3 Mn 4+ (SO 4 ) 2 (OH) 6 · 3H 2 O . In: Acta Crystallographica . E67, 2011, p. i47 – i48 , doi : 10.1107 / S1600536811030911 ( rruff.info [PDF; 1.1 MB ; accessed on December 3, 2018]).
  12. ↑ a b c Georg Gebhard: Tsumeb: a German-African story . 1st edition. GG Publishing, Reichshof 1991, ISBN 978-3-925322-02-0 , pp. 194 .
  13. ↑ a b Paul Keller: Tsumeb / Namibia - one of the most spectacular mineral discovery sites on earth . In: Lapis . tape 9 , no. 7/8 , 1984, pp. 13-63 .
  14. ↑ Localities for site. In: mindat.org. Hudson Institute of Mineralogy, accessed May 12, 2019 .
  15. ↑ Find location list for Schaurteit at the Mineralienatlas and at Mindat