Söhngeit

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Söhngeit
Söhngeite-339161.jpg
Söhngeit from the Tsumeb Mine, Namibia (image size: 6.5 mm)
General and classification
other names

IMA 1965-022

chemical formula Ga (OH) 3
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FC.05 ( 8th edition : IV / F.06)
03/06/05/02
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-pyramidal; mm 2
Space group Pmn 2 1 (No. 31)Template: room group / 31
Lattice parameters a  = 7.4865  Å ; b  = 7.4379 Å; c  = 7.4963 Å
Formula units Z  = 8
Physical Properties
Mohs hardness 4 to 4.5
Density (g / cm 3 ) measured: 3.84 (synthetic); calculated: 3.847
Cleavage "Hint of cubic cleavage"
Break ; Tenacity not specified
colour white, light yellow, light brown, light greenish yellow
Line color White
transparency transparent to translucent
shine not specified
Crystal optics
Refractive index n  = 1.736
Other properties
Chemical behavior soluble in hydrochloric acid and sulfuric acid

Söhngeit is a very rarely occurring mineral from the mineral class of "oxides and hydroxides" with the chemical composition Ga (OH) 3 and thus, chemically speaking, gallium hydroxide .

Söhngeit crystallizes in the orthorhombic crystal system and develops pseudocubic crystals as well as characteristically formed crystal twins and mineral aggregates of up to one centimeter in size. In its pure form, Söhngeit is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also be translucent white and, due to foreign admixtures, take on a light yellow, light brown or light greenish yellow color.

Etymology and history

Hugo Strunz is considered to be the discoverer of Söhngeits, who found the mineral on clearly secondarily converted germanite specimens with gallite segregation that were collected in early 1965. Corresponding investigations led to the determination of the presence of a new mineral, which was recognized by the IMA in 1965 . A little later, in 1965, Hugo Strunz described the mineral as Söhngeit in a short article. The mineral was named after the geologist Adolf Paul Gerhard Söhnge (1913-2006), who was chief geologist at the Tsumeb mine in Namibia from 1950 to 1968 .

The type material of the mineral is kept at the Technical University of Berlin (Cotyp, collection no. 86/69 at location 89-1).

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the Söhngeit belonged to the mineral class of "oxides and hydroxides" and there to the department of "hydroxides", where together with Stottit the "Söhngeit-Stottit group" with the system no. IV / F.06 and the other members Dzhalindit and Wickmanit .

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. IV / F.15-10 . In the "Lapis system" this also corresponds to the class "Oxides and Hydroxides", but there the department "Hydroxides and oxidic hydrates (water-containing oxides with layer structure)", where Söhngeit forms an independent, but unnamed group together with Dzhalindit and Bernalit .

The 9th edition of Strunz's mineral systematics, which has been valid since 2001 and has been updated by the International Mineralogical Association (IMA) and updated until 2009, classifies the Söhngeit in the category of "hydroxides (without U and V)". This is further subdivided according to the possible presence of hydroxide ions and crystal water as well as the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “Hydroxides with OH, without H 2 O; corner-linked octahedron ”can be found where the name giver of the" Söhngeitgruppe "with the system no. 4.FC.05 is. The Söhngeit group still includes Söhngeit, Dzhalindit and Bernalit.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Söhngeit to the class of "oxides and hydroxides" and there in the department of "hydroxides and hydroxide-containing oxides". Here it can be found in the unnamed group 06.03.05 within the subsection “Hydroxides and hydroxides containing (OH) 3 or (OH) 6 groups”.

Chemism

Söhngeit was described in 1965 as the "first oxidic gallium mineral " and has remained the only mineral with gallium as the main component to this day. Ideal Ga (OH) 6 consists of 77.62% Ga 2 O 3 and 22.38% H 2 O, whereas smaller amounts of silicon , aluminum and iron have been detected in the analyzed Söhngeit crystals .

Crystal structure

Söhngeit crystallizes orthorhombically in the space group Pmn 2 1 (space group no. 31) with the lattice parameters a  = 7.4865  Å ; b  = 7.4379 Å and c  = 7.4963 Å and 8 formula units per unit cell . Template: room group / 31

The crystal structure of the Söhngeits shows gallium in an almost centric arrangement. The oxygen atoms form disturbed octahedra around the gallium. The octahedra are linked by corners and come together to form an infinite framework.

properties

Drawing of Söhngeit crystals that have grown together to form an idealized hypothetical triplet

morphology

Söhngeit forms flat to tabular, curved crystals that come together to form strange aggregates up to 1 cm in size. Characteristic is the oriented intergrowth of the individual crystals at an angle of 90 ° to form crystal aggregates, which can be seen in the drawing on the left. These aggregates are also discussed as multiple penetration twinning according to an unknown law, which simulate a cubic crystal shape. The crystals are often partially dissolved and can only be identified visually if the characteristic aggregates or penetration twins are present.

For a long time it was assumed that all Söhngeite show the adhesions described, but tabular single crystals up to 10 mm in size and transparent, non-twinned, pseudocubic crystals up to 1 mm in size are also known.

physical and chemical properties

The translucent to transparent crystals and aggregates of the Söhngeits are white, pale yellow, pale brown, pale greenish-yellow or brown, the color of the streak is indicated as white.

The mineral shows “a hint of cubic cleavage”, so it can be cleaved easily or indistinctly in three directions according to {100}, {010} and {001}. With a Mohs hardness of 4 to 4.5, Söhngeit is one of the medium-hard minerals that are somewhat easier to scratch with a pocket knife than the reference mineral apatite . The measured density of synthesized equivalents of the mineral is 3.84 g / cm³, its calculated density is 3.847 g / cm³.

Söhngeit is readily soluble in hydrochloric acid (hydrogen chloride) and sulfuric acid .

Education and Locations

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

Söhngeit is a typical secondary mineral and formed in the second (lower) oxidation zone in dolomite stones seated hydrothermal polymetallic ore deposit Tsumeb. It originated from gallium-containing germanite from the Tsumeb ore body . The mineral is typically located in holey eroded germanite, which contains gallite segregation bodies. Typical sites in Tsumeb were areas on the level between 900 m and 1100 m depth.

See also

literature

  • Hugo Strunz : Söhngeit, Ga (OH) 3 , a new mineral . In: The natural sciences . tape 52 , no. 17 , September 1, 1965, pp. 493 , doi : 10.1007 / BF00646572 .
  • Söhngeite . 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; 70 kB ; accessed on May 20, 2019]).

Web links

Commons : Söhngeite  - 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: March 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2019, accessed May 20, 2019 .
  2. ↑ a b c d e f JD Scott: Crystal structure of a new mineral, söhngeite . In: American Mineralogist . tape 56 , 1971, p. 355–355 (English, rruff.info [PDF; 67 kB ; accessed on May 20, 2019]).
  3. ↑ a b c d e f g h i j Hugo Strunz : Söhngeit, Ga (OH) 3 , a new mineral . In: The natural sciences . tape  52 , no. 17 , September 1, 1965, pp. 493 , doi : 10.1007 / BF00646572 .
  4. ↑ a b c d e Söhngeite . 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; 70  kB ; accessed on May 20, 2019]).
  5. ↑ a b 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 .
  6. ↑ a b Mineralienatlas: Söhngeit (Wiki)
  7. ^ Gerhard Söhnge: Journal of a geologist . 1st edition. Stellenbosch University Ptrinters, Stellenbosch 2001, ISBN 0-7972-0880-1 , p. 115-147 .
  8. ↑ R. Kurtz: Type Mineral Catalog Germany - Söhngeit. In: typmineral.uni-hamburg.de. University of Hamburg, December 8, 2017, accessed on May 20, 2019 .
  9. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 25, 2019 .
  10. ^ A b William W. Pinch, Wendell E. Wilson: Minerals: a descriptive list . In: Mineralogical Record . tape 8 , no. 3 , 1977, pp. 17-36 (English).
  11. ↑ a b Paul Keller : Tsumeb / Namibia - one of the most spectacular mineral discovery sites on earth . In: Lapis . Special issue Tsumeb. tape  9 , no. 7/8 , 1984, pp. 13-63 .
  12. ^ Georg Gebhard: Tsumeb: A Unique Mineral Locality . 1st edition. GG Publishing, Grossenseifen 1999, ISBN 978-3-925322-03-7 , pp. 274-275 (English).
  13. ↑ Localities for Söhngeite. In: mindat.org. Hudson Institute of Mineralogy, accessed May 20, 2019 .
  14. ↑ Find location list for stottite in the Mineralienatlas and Mindat