Galloplumbo rubber

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Galloplumbo rubber
Galloplumbogummite.jpg
White galloplumbo gumite crystals
General and classification
other names

IMA 2010-088

chemical formula
  • Pb (Ga, Al) 3 – x Ge x H 1 – x (PO 4 ) 2 (OH) 6 for 0 ≤ x ≤ 1 or
  • Pb (Ga, Al, Ge) 3 (PO 4 ) 2 (OH) 6 for x = 1
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. according to Strunz 8.BL.10
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3  2 / m
Space group R 3 m (No. 166)Template: room group / 166
Lattice parameters a  = 7.083  Å ; c  = 16.742 Å
Formula units Z  = 3
Frequent crystal faces {h0 h l}, {hk i l} or {0k k l}, {0001}
Physical Properties
Mohs hardness not definable
Density (g / cm 3 ) 4.62 (calculated)
Cleavage not specified
Break ; Tenacity not specified; not specified
colour colorless, matt white
Line color White
transparency not specified
shine not specified
Crystal optics
Refractive index n  = 1.82
Optical character uniaxial positive

Galloplumbogummit is a very rare mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the trigonal crystal system with the chemical formula Pb (Ga, Al) 3 − x Ge x H 1 − x (PO 4 ) 2 (OH) 6 for 0 ≤ x ≤ 1 or Pb (Ga, Al, Ge) 3 From a chemical point of view, (PO 4 ) 2 (OH) 6 for x = 1 is therefore a lead - gallium phosphate with additional hydroxide ions and, as a representative of the plumbogummite subgroup within the alunite supergroup, the Ga-dominant analogue of plumbogummite there .

Galloplumbo gum forms colorless rhombohedral crystals up to 0.15 mm in size, which typically have a matt white “frosted” shell. White, spherical aggregates were also observed. The mineral was in millimeter-sized cavities in massive germanite - Renierit - ore found the "Tsumeb Mine" in Namibia.

Etymology and history

Galloplumbo rubber was discovered in 2003 as a Ga-dominant plumbo rubber in the collection of the Mineralogical Museum Hamburg in a suite of ore stages from the "Tsumeb Mine". The original stage was bequeathed to the museum by Professor Hermann Rose (1883–1976), who visited South West Africa , now Namibia , in 1939 for scientific research. Since the process of characterizing the new mineral turned out to be very complex, the corresponding test results could not be transmitted to the International Mineralogical Association (IMA) until 2010 , which recognized the mineral in the same year under the number IMA 2010-088. In 2014 it was described by a German research team with Jochen Schlueter , Thomas Malcherek and Boriana Mihailova in the German science magazine “New Yearbook for Mineralogy, Treatises” as galloplumbo rubber. The mineral was named for its chemical composition with gallium and its structural relationship to plumbogummite.

Type material of the mineral (holotype) is kept in the Mineralogical Museum of the University of Hamburg in Germany (catalog no. TS 531). It is a sample from the former Hermann Hähnel collection, Hamburg, and material from Hermann Rose.

Various Gallium-rich representatives of the Alunit supergroup have been known from the Tsumeb Mine for a long time. The gallium-dominant analogue of Beudantite was described in 1996 as gallobeudantite . A gallium-rich plumbogummite, which sits on gallite- renierite-germanite ore in the form of white crystals up to 300 μm in size together with gallium-rich arsenocrandallite and an unknown Zn-Fe-Ga oxide , had already been presented in 2009.

classification

Galloplumbo gum was only recognized as an independent mineral by the International Mineralogical Association (IMA) in 2010 and the discovery was only published in 2014. A precise group assignment in the 9th edition of Strunz's mineral classification is therefore not yet known. If one follows the nomenclature of the alunite supergroup in the classification of John L. Jambor (1999) or the recommendations of Peter Bayliss and coworkers (2010), the galloplumbogummite within the alunite supergroup can be most likely paralleled with the minerals of the crandallite group.

Since galloplumbo gum is a close relative of plumbo gum, which due to its composition can be found in the mineral class of "phosphates, arsenates and vanadates", galloplumbo gum is also likely to be classified there. 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 plumbogummite to the class of "phosphates, arsenates and vanadates" and there to the department of "phosphates, etc. with additional anions; without H 2 O “. However, this section is further subdivided according to the size of the cations involved and the ratio of the other anions to the phosphate, arsenate or vanadate complex RO 4 , so that the mineral can be classified in the sub-section “With medium-sized and large cations (OH, etc.” .): RO 4  = 3: 1 “can be found where, together with arsenocrandallite, arsenogorceixite , arsenogoyazite , benauite , crandallite , Dussertite , Gorceixite , goyazite , kintoreit , Philipsbornite , plumbogummit, segnitite and springcreekite, the crandallite group with the system number 8.BL.10 forms.

Chemism

Mean values ​​from 14 microprobe analyzes on galloplumbo gum from Tsumeb led to contents of 34.45% PbO, 0.42% CaO, 10.19% Al 2 O 3 , 19.64% Ga 2 O 3 , 5.93% GeO 2 , 0 , 20% Fe 2 O 3 , 20.04% P 2 O 5 , 1.71% SO 3 and 7.42% H 2 O. This resulted in the empirical formula (based on 14 oxygen atoms per formula unit) (Pb 1.04 Ca 0.05 ) Σ = 1.09 (Ga 1.41 Al 1.35 Ge 0.38 Fe 0.02 ) Σ = 3.16 (P 1.91 S 0.14 ) Σ = 2, 05 O 8.44 (OH) 5.56 , which has been simplified to Pb (Ga, Al) 3-x Ge x H 1-x (PO 4 ) 2 (OH) 6 for 0 x 1. The highest gallium value found in the sample was 26.03% Ga 2 O 3 , accompanied by 8.59% GeO 2 . The highest germanium value was found to be 10.93% GeO 2 . In a galloplumbo rubber sample from the Royal Ontario Museum in Toronto / Canada , a gallium content of 2.28 per formula unit was even detected in a galloplumbo rubber sample from the "Tsumeb Mine". Overall, the galloplumbogummite crystal examined in the type publication exhibited an extremely strong chemical zoning with substitution of Al / Ga / Ge as well as Pb / Ca and P / S.

Crystal structure

Galloplumbo rubber crystallizes trigonal in the space group R 3 m (space group no. 166) with the lattice parameters a  = 7.083  Å and c  = 16.742 Å as well as three formula units per unit cell . Template: room group / 166

properties

morphology

Galloplumbo rubber forms rhombohedral crystals up to 0.15 mm in size, on which a ditrigonal scalenohedron {hk i l} or {0k k l} has been proven in addition to a rhombohedron I position determining the costume {h0 k l} and the base pinacoid {0001} . There are also spherical aggregates.

physical and chemical properties

Galloplumbo rubber crystals are colorless and typically have a matt white "frosted" shell. Spherical aggregates are white. The line color of the galloplumbo gum, however, is always white. There is no information on the transparency and shine of the mineral or its cleavage . Because of the small crystal size of galloplumbo rubber, neither its Mohs hardness nor Vickers hardness could be determined. Measured values ​​for the density of galloplumbo gum do not exist; the calculated density for the mineral is 4.62 g / cm³.

Education and Locations

Galloplumbogummit arises as a typical secondary formation in a complex, seated in carbonate rocks Cu-Pb-Zn ore - deposit in the alteration of the germanium and gallium-rich ores. Lead, gallium and germanium come from the decomposition of former sulphide ore minerals such as galena, germanite and renierite. Galloplumbo gum occurs in millimeter-sized cavities in the germanite - renierite ore of the "Tsumeb Mine" in Namibia and is accompanied by chalcosine , Cd-rich sphalerite , galena and pyrite (samples in the Mineralogical Museum Hamburg). A sample from the Royal Ontario Museum in Toronto shows galloplumbo gum in white, spherical aggregates next to otjisumeit on germanite.

As a very rare mineral formation, galloplumbo gum could only be described from one source so far (as of 2016). Its type locality 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, galloplumbo gum is only of interest to mineral collectors.

See also

literature

  • Gunadi Adiwidjaja, Karen Friese, Karl-Heinz Klaska, Jochen Schlüter, M. Czank: Crystal structure and crystal chemistry of biehlite, Sb 1.79 As 0.21 MoO 6 . In: Journal of Crystallography . tape 215 , 2000, pp. 529–535 , doi : 10.1524 / zkri.2000.215.9.529 ( rruff.info [PDF; 909 kB ]).
  • Galloplumbogummit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 286 kB ).

Web links

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

Individual evidence

  1. ↑ a b c d e f g h i j k l m Jochen Schlüter, Thomas Malcherek, Boriana Mihailova: Galloplumbogummite from Tsumeb, Namibia, a new member of the alunite group with tetravalent charge balance . In: New Yearbook for Mineralogy, Treatises . tape 191/3 , 2014, p. 301–309 , doi : 10.1127 / 0077-7757 / 2014/0262 .
  2. ↑ Typmineral catalog Germany - storage of the holotype stage Galloplumbogummit
  3. ^ A b Stuart J. Mills, Anthony R. Kampf, Mati Raudsepp, Andrew G. Christy: The crystal structure of Ga-rich plumbogummite from Tsumeb, Namibia . In: Mineralogical Magazine . tape 73 , 2009, pp. 837-845 , doi : 10.1180 / minmag.2009.073.5.837 .
  4. ↑ a b c Peter Bayliss, Uwe Kolitsch, Ernest H. Nickel, Allan Pring: Alunite supergroup: recommended nomenclature . In: Mineralogical Magazine . tape 74 , 2010, pp. 919–927 , doi : 10.1180 / minmag.2010.074.5.919 ( cnmnc.main.jp [PDF; 210 kB ]).
  5. ↑ John Leslie Jambor , DeAlton R. Owens, Joel D. Grice, Mark N. Feinglos: Gallobeudantite, PbGa 3 [(AsO 4 ), (SO 4 )] 2 (OH) 6 , a new mineral species from Tsumeb, Namibia, and associated new gallium analogues of the alunite-jarosite family . In: The Canadian Mineralogist . tape  34 , 1996, pp. 1305–1315 ( rruff.info [PDF; 1.9 MB ]).
  6. ^ A b John Leslie Jambor : Nomenclature of the Alunite supergroup . In: The Canadian Mineralogist . tape  37 , 1999, pp. 1323-1341 ( PDF rruff.info ).
  7. ↑ Mindat - mineral description Galloplumbogummit
  8. ↑ Mindat - Number of localities for Galloplumbogummit
  9. ↑ a b List of places where galloplumbogummite was found in the Mineralienatlas and Mindat