Tsumgallit

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Tsumgallit
General and classification
other names

IMA 2002-011

chemical formula
  • GaO (OH)
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FD.10 ( 8th edition : IV / F.06)
01/06/01/06
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pnma (No. 62)Template: room group / 62
Lattice parameters a  = 4.512  Å ; b  = 9.772 Å; c  = 2.967 Å
Formula units Z  = 4
Physical Properties
Mohs hardness "Soft", probably 1 to 2
Density (g / cm 3 ) 5.22 (ideal composition), 5.08 (empirical formula)
Cleavage excellent parallel {010}
Break ; Tenacity not specified; not specified
colour pale greenish yellow to beige
Line color White
transparency translucent
shine Pearlescent
Crystal optics
Refractive index n  = 1.96 (ideal composition), 1.97 (empirical formula)
Optical character biaxial

Tsumgallite is a very rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the cubic crystal system with the chemical composition GaO (OH) and is thus chemically seen a gallium - oxide - hydroxide .

Tsumgallite develops thin-plate crystals up to 40 × 40 µm in size and 0.5 to 1 µm thick, which come together to form flaky, mica-like aggregates . They sit in cavities in the ore rich in germanite - tennantite - which contains inclusions of gallite . Accompanying minerals are söhngeit , zinc-rich siderite , chalcosine and quartz .

Etymology and history

Tsumgallite was discovered on a mineral specimen collected by former Tsumeb Mine geologist and chief mineralogist of Tsumeb Corporation Limited Bruno Herrmann Geier (1902-1987) in the second oxidation zone of the Tsumeb Mine in the early 1960s. His son Ulf Geier made this mineral available to the authors of the type publication for identification.

Corresponding investigations led to the determination of the presence of a new mineral, which was recognized by the International Mineralogical Association (IMA) on June 5, 2002 and described as tsumgallite in 2003 by a German research team including Jochen Schlüter , Karl-Heinz Klaska , Gunadi Adiwidjaja and Georg Gebhard . The mineral was named after Tsumeb or the Tsumeb Mine and its main component gallium . Tsumgallite is the fifth mineral after tsumebite and arsentsumebite as well as tsumcorite and plumbotsumite , the name of which refers to tsumeb or the tsumeb mine.

Type material of the mineral is kept in the Mineralogical Museum of the University of Hamburg in Germany (holotype, collection no. MMHH TS 509, in the safe of the museum).

classification

In the outdated but still partially in use 8th edition of the mineral classification by Strunz of Tsumgallit belonged to the mineral class of "oxides and hydroxides" and then to the Department of "hydroxides and oxide hydrates" where he along with akaganeite , boehmite , diaspore , Feitknechtit , Feroxyhyt , goethite , groutite , lepidocrocite , manganite and sword mannite formed the unnamed group IV / F.6 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns tsumgallite to the class of "oxides and hydroxides" and then to the "hydroxides (without V or U)" category . However, this section is further subdivided according to the possible presence of crystal water and according to the crystal structure, so that the mineral is classified according to its composition in the sub-section “Hydroxides with OH, without H 2 O; can be found with chains of edge-sharing octahedra "where it, along with diaspore Bracewellit , goethite, Groutit, Guyanait and montroseite the unnamed group 4.FD.10 forms.

The systematics of minerals according to Dana also assigns the tsumgallite to the class of "oxides and hydroxides" and there in the department of "hydroxides and hydroxides containing oxides". Here he is together with the eponymous Diaspor and the other members Goethit, Groutit, Montroseit and Bracewellit in the "Diaspor group (Orthorhombic, Pnma or Pnmd)" with the system no. 06.01.01 to be found within the sub-section of " Hydroxides and hydroxide-containing oxides with the formula: X 3+ O OH ".

Chemism

Tsumgallite has (based on two anions) the measured composition (Ga 0.86 Fe 3+ 0.05 Ge 0.04 Si 0.02 Zn 0.01 ) Σ0.98 O 1.00 (OH) 1.00 , which has been idealized to GaO (OH) and requires levels of 91.23% Ga 2 O 3 and 8.77% H 2 O. Tsummgallit represents the Ga-dominant member of the diaspora group and from a chemical point of view therefore z. B. represents the gallium-dominant analogue to the Al-dominated diaspore, to the Fe 3+ -dominated lepidocrocite and goethite, to the Mn 3+ -dominated manganite and groutite and to the Cr-dominated bracewillite and guyanaite. Tsumgallite is that according to Gallit, Söhngeit , Gallobeudantite and galloplumbo gum are only the fifth mineral with gallium as the main component.

Crystal structure

Tsumgallite crystallizes in the orthorhombic crystal system in the space group Pnma (space group no. 62) with the lattice parameters a  = 4.512  Å ; b  = 9.772 Å and c  = 2.967 Å as well as four formula units per unit cell . Template: room group / 62

Tsumgallite, just like its synthetic equivalent, α-gallium oxide-deuteriohydroxide, is isotype (isostructural) with goethite and diaspore. The crystal structure of tsumgallite can therefore be described in analogy to that of diaspore. Oxygen and hydroxide ions form a hexagonal close packing of spheres with gaps in the octahedron spaces that are filled by gallium. In this way, long double chains of GaO 6 octahedra are created in the direction of the c-axis , which are held together by hydrogen bonds .

properties

morphology

Tsumgallite was found in the form of flaky to mica-like , clearly porous aggregates consisting of thin-plate crystals up to 40 × 40 µm in size and 0.5 to 1 µm thick.

physical and chemical properties

The tsumgallite crystals are pale greenish yellow to beige in color , the color of the streak is described as white. The surfaces of the translucent crystals show a pearlescent sheen .

The mineral has excellent cleavage surfaces parallel {010}. Tsumgallite is described as "soft", which corresponds to a Mohs hardness of 1 to 2. This makes tsumgallite one of the minerals that are slightly easier to scratch with the fingernail than the reference mineral gypsum . The calculated density for the empirical formula of the tsumgallite is 5.08 g / cm³. The mineral does not fluoresce in the long or short wave UV range.

Education and Locations

As a very rare mineral formation Tsumgallit has so far only by his (2016 version) type locality are described. This is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia , where Tsumgallite was recovered only once in the second oxidation zone , albeit at an unknown depth is. Here it was found on a germanite-tennantite-rich ore with inclusions of gallite. For Paragenesis also include colorless or white, slightly etched Söhngeit crystals to 5 mm size, reddish brown, rhombohedral crystals of a zinc-rich Siderits up to 0.5 mm size, as well as quartz and chalcocite.

Tsumgallit is a typical secondary mineral and in formed in the second oxidation zone dolomite stones seated hydrothermal polymetallic ore deposit Tsumeb from gallium-Primärerzmineralen.

use

With a Ga 2 O 3 content of 91%, the mineral would be an exceptionally rich gallium ore, but due to its extreme rarity, the mineral is only of interest to mineral collectors.

See also

literature

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w x Jochen Schlüter, Karl-Heinz Klaska, Gunadi Adiwidjaja, Georg Gebhard (2003): Tsumgallite, GaO (OH), a new mineral from the Tsumeb mine, Tsumeb, Namibia. In: New Yearbook Mineralogy, monthly books. Volume 2003 (Issue 11), pp. 521-527 Doi: 10.1127 / 0028-3649 / 2003 / 2003-0521 .
  2. ^ Joseph Anthony Mandarino (2000): New Minerals. In: The Canadian Mineralogist. Volume 42, p. 941 ( PDF, 333 kB ).
  3. ↑ Type mineral catalog Germany - storage of the holotype stage Tsumgallit
  4. ↑ Mindat - Number of localities for Tsumgallit
  5. ↑ Find location list for tsumgallite at the Mineralienatlas and at Mindat