Gerdtremmelit

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Gerdtremmelit
Gerdtremmelite.jpg
Brown aggregates of tiny gerdtremmelite crystals from the Tsumeb Mine near Tsumeb , Oshikoto Region , Namibia
General and classification
other names

IMA 1983-049a

chemical formula
  • (Zn, Fe) (Al, Fe) 2 [(OH) 5 | AsO 4 ]
  • (Zn, Fe) (Al, Fe) 2 (AsO 4 ) (OH) 5
  • (Zn, Fe 2+ ) (Al, Fe 3+ ) 2 (AsO 4 ) (OH) 5
  • ZnAl 2 (AsO 4 ) (OH) 5
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.BE.40 ( 8th edition : VII / B.16)
03.41.07.01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1 or triklin-pedial; 1
Space group P 1 (No. 2) or P 1 (No. 1)Template: room group / 2Template: room group / 1
Lattice parameters a  = 5.169  Å ; b  = 13.038 Å; c  = 4.931 Å,
α  = 98.78 °; β  = 100.80 °; γ  = 78.73 °
Formula units Z  = 2
Physical Properties
Mohs hardness not definable
Density (g / cm 3 ) > 3.3 (measured), 3.66 (calculated for iron-containing mixed crystal)
Cleavage no
Break ; Tenacity no break observed
colour brown, yellow brown and dark brown in different shades of color
Line color White
transparency transparent
shine Diamond luster
Crystal optics
Refractive indices n α  = 1.730 to 1.740
n γ  = 1.830 to 1.840
Refractive index n  = 1.73 to 1.74
Birefringence δ = 0.100
Optical character biaxial
Other properties
Chemical behavior insoluble in cold and warm HCl

Gerdtremmelite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the triclinic crystal system with the chemical composition (Zn, Fe 2+ ) (Al, Fe 3+ ) 2 [(OH) 5 | AsO 4 ] and is chemically a zinc - aluminum - iron - arsenate with additional hydroxide ions .

Gerdtremmelit develops spherical-spherulitic aggregates at its type locality , which are made up of tabular crystals up to 3 µm in size and 1 µm thick. They are accompanied u. a. of hematite , quartz , scorodite , powellite , betpakdalite and kaolinite .

The type locality of the mineral is the so-called second oxidation zone of the Tsumeb Mine near Tsumeb , Oshikoto Region , Namibia .

Etymology and history

At the beginning of the 1980s Karl Schmetzer , Bernhard Nuber and Gerd Tremmel discovered an unknown Zn-Fe-Al-arsenate, which turned out to be a new one, during an investigation of Betpakdalites (today Betpakdalit-CaCa ) from the Tsumeb Mine in the paragenesis of one of the investigated stages Phase turned out. The two mineralogists Karl Schmetzer from the Mineralogical-Petrographic Institute of the Ruprecht-Karls-Universität Heidelberg and Olaf Medenbach from the Institute for Mineralogy of the Ruhr University Bochum carried out the investigations necessary for a characterization as a new mineral and presented the results to the International Mineralogical Association ( IMA), which recognized this mineral under the provisional designation IMA 1983-049a in 1983. In 1985, both scientists published the first scientific description of this mineral as Gerdtremmelite ( English Gerdtremmelite ) in the German science magazine “New Yearbook for Mineralogy, Monthly Issues ”. The authors named the mineral after the German mineralogist and mineral collector Gerd Tremmel (* 1940) from Overath-Steinenbrück , who, as a specialist in minerals from Tsumeb, had made the type material available for analysis. Tremmel was u. a. Co-author of the first description of the arhbarite .

The type material for Gerdtremmelite (holotype stage, catalog no. 10'11'16) is in the mineral collection of the Mineralogical-Petrographic Institute of the University of Heidelberg and under catalog number 147360 (type stage) in the collection of the National Museum of Natural History belonging to the Smithsonian Institution , Washington, DC , USA .

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the gerdtremmelite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "anhydrous phosphates, with foreign anions F, Cl, O, OH", where he formed the unnamed group VII / B.16 as the sole representative .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the IMA, also assigns Gerdtremmelit to the class of “phosphates, arsenates and vanadates” and there to the category of “phosphates etc. with additional anions; without H 2 O “. However, this section is now more precisely subdivided according to the size of the cations involved and the ratio between the other anions and the phosphate, arsenate or vanadate complex, so that the mineral is classified according to its composition in the sub-section “With only medium-sized cations (OH, etc.) .): RO 4  > 2: 1 “can be found, where it is the only member of the unnamed group 8.BE.40 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns gerdtremmelite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here he is to be found as the sole representative in the unnamed group 41.03.07 within the subdivision of " Anhydrous phosphates etc., with hydroxyl or halogen with (AB) 3 (XO 4 ) Z q ".

Chemism

From a series of microprobe analyzes it became clear that Gerdtremmelite is a hydrous zinc-iron-aluminum arsenate with variable amounts of ZnO, Fe 2 O 3 and Al 2 O 3 and that divalent iron (Fe 2+ ) is zinc and trivalent iron ( Fe 3+ ) can replace the aluminum in the structure of Gerdtremmelite. Furthermore, an iron-free end link of a mixed crystal row with the iron-containing Gerdtremmelite seems to exist.

A microprobe analysis on a Gerdtremmelite from the Tsumeb mine showed values ​​of 19.51% ZnO; 0.01% CuO; 1.08% MoO 3 ; 11.38% Fe 2 O 3 ; 23.76% Al 2 O 3 ; 32.53% As 2 O 5 and 11.25 H 2 O ( determined thermogravimetrically ), from which the empirical formula (Zn 0.83 Fe 0.49 Al 1.60 ) Σ = 2.92 [(As 0.97 Mo 0.03 ) Σ = 1.00 O 4 ] (OH) 4.30 . An idealized formula with (Zn 0.85 Fe 2+ 0.15 ) Σ = 1.00 (Al 1.70 Fe 3+ 0.30 ) Σ = 1.00 (AsO 4 ) (OH) 5 would result in contents of 19 , 73% ZnO; 6.83% Fe 2 O 3 ; 3.07% FeO; 24.73% Al 2 O 3 ; 32.79% As 2 O 5 and 12.85 H 2 O require, an ideally iron-free end link with the composition ZnAl 2 [(AsO 4 ) | (OH) 5 ] requires levels of 23.70% ZnO; 29.70% Al 2 O 3 ; 33.48% As 2 O 5 and 13.12 H 2 O.

In chemical terms, gerdtremmelite is not related to other minerals. Another mineral with only Zn, Al, Fe, As, O and H does not exist, the only other mineral with only Zn, Al, As, O and H is an aluminum-containing adamin .

Crystal structure

Gerdtremmelite crystallizes in the triclinic crystal system in space group P 1 (space group no. 2) or space group P 1 (space group no. 1) with the lattice parameters a  = 5.169  Å ; b  = 13.038 Å; c  = 4.931 Å; α = 98.78 °; β = 100.80 ° and γ = 78.73 ° as well as two formula units per unit cell . Template: room group / 2 Template: room group / 1

The crystal structure of gerdtremmelite is still unknown.

properties

morphology

Gerdtremmelit develops spherical-spherical aggregates from 0.5 to almost 1 mm in diameter, which are composed of tabular crystals up to 3 µm in size and 1 µm in thickness. According to other information, the tabular crystals are larger and reach sizes up to 0.5 mm.

physical and chemical properties

The crystals of Gerdtremmelite are brown, yellow-brown and dark brown in different shades, but their line color is always white. The surfaces of the transparent crystals have a diamond-like sheen , which agrees well with the values ​​for light refraction . High values ​​for light refraction (n α  = 1.730–1.740; n γ  = 1.830–1.840) and very high values ​​for birefringence (δ = 0.100) were found on the crystals of Gerdtremmelite .

Gerdtremmelit is neither cleavable nor broken . There is no information on tenacity or values ​​for Mohs hardness , which could not be determined due to the limited amount of material available. The measured density for Gerdtremmelite is> 3.3 g / cm³, the calculated density for the mineral is 3.66 g / cm³ (calculated for iron-containing mixed crystal) or 3.59 g / cm³ (calculated for the iron-free end member of the mixed crystal row).

Gerdtremmelit is neither in the long term nor in the short wavelength UV light , a fluorescent .

The mineral dissolves neither in cold nor in warm hydrochloric acid , HCl.

Education and Locations

As an extremely rare mineral formation (fewer than ten stages are known) Gerdtremmelite could only be described from one site so far (as of 2018). The type locality is the “Tsumeb Mine” near Tsumeb, Oshikoto region , Namibia , with the exact location within the mine being the second oxidation zone. Occurrences of Gerdtremmelite in Germany , Austria or Switzerland are therefore not known.

Gerdtremmelit is a typical secondary mineral , which in the oxidation zone an arsenic-rich polymetallic non-ferrous metal - deposit has formed. The zinc comes from the weathering of sphalerite , the arsenic from oxidized tennantite, the iron possibly also from the sphalerite or from the weathering of pyrite or chalcopyrite from the primary ores. The aluminum is very likely to be derived from the host rock . In the “Tsumeb Mine”, gerdtremmelite was found grown on intensely oxidized layers in hematite and quartz. Further paragenesis minerals are scorodite, the molybdates powellite and betpakdalite (more precisely Betpakdalit-CaCa) and kaolinite.

Later finds on the 44th level in the area of ​​the so-called third oxidation zone yielded significantly better crystallized material with tan-colored gerdtremmelite single crystals less than 1 mm in size on pale blue, aluminum-containing scorodite (approx. 10% by weight Al 2 O 3 ), the were accompanied by excellently trained Wilhelmkleinit crystals and Adamin .

use

Gerdtremmelite is only of interest to mineral collectors due to its extreme rarity.

See also

literature

  • Karl Schmetzer, Olaf Medenbach: Gerdtremmelite, (Zn, Fe) (Al, Fe) 2 [(AsO 4 ) | (OH) 5 ], a new mineral from Tsumeb, Namibia . In: New yearbook for mineralogy, monthly books . tape 1985 , no. 1 , 1985, pp. 1-6 .
  • Gerdtremmelite . 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; 64 kB ; accessed on July 24, 2018]).

Web links

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

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 y z aa ab ac ad ae Karl Schmetzer, Olaf Medenbach: Gerdtremmelite, (Zn, Fe) (Al, Fe) 2 [(AsO 4 ) | (OH) 5 ], a new mineral from Tsumeb, Namibia . In: New yearbook for mineralogy, monthly books . tape 1985 , no. 1 , 1985, pp. 1-6 .
  2. ^ Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  450 .
  3. ↑ a b c d e f g h Mindat - Gerdtremmelite (English)
  4. ↑ a b c Gerdtremmelite . 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; 64  kB ; accessed on July 24, 2018]).
  5. ^ IMA / CNMNC List of Mineral Names; March 2018 ( Memento from June 11, 2018 in the Internet Archive ) (PDF 1.65 MB)
  6. ^ Karl Schmetzer, Bernhard Nuber, Gerd Tremmel: Betpakdalit from Tsumeb, Namibia: Mineralogy, crystal chemistry and structure . In: New yearbook for mineralogy, monthly books . tape 1984 , 1984, pp. 393-403 .
  7. ^ Karl Schmetzer, Gerd Tremmel, Olaf Medenbach: Arhbarite, Cu 2 [OH | AsO 4 ] · 6H 2 O, a new mineral from Bou-Azzer, Morocco . In: New yearbook for mineralogy, monthly books . tape 1982 , 1982, pp. 529-533 .
  8. ↑ Commission on Museums (IMA): Catalog of Type Mineral Specimens - Storage of the type material for Gerdtremmelite ( Memento of March 28, 2017 in the Internet Archive )
  9. ↑ a b c Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, ISBN 3-925322-03-5 , pp. 216, 256-257, 271-272 .
  10. ↑ Webmineral - Gerdtremmelite (English)
  11. ↑ Mindat - Number of localities for Gerdtremmelit
  12. ↑ a b List of localities for Gerdtremmelite in the Mineralienatlas and Mindat
  13. ↑ Tsumeb.com - Gerdtremmelite (English)