Torbernite

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Torbernite
Torbernite-120981.jpg
Torbernite crystals from the Mashamba West Mine, Kolwezi, Katanga , Democratic Republic of the Congo
Size: 3.2 × 2.5 × 1.4 cm
General and classification
other names
  • Chalcolite
  • Green mica
  • Copper autunit
  • Copper phosphorururanite
  • Copper uranium mica
  • Mica viridis cryst.
chemical formula Cu [UO 2 | PO 4 ] 2 • 12H 2 O
Mineral class
(and possibly department)
Phosphates , arsenates and vanadates
System no. to Strunz
and to Dana
8.EB.05 ( 8th edition : VII / E.01)
40.02a.13.01
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal; 4 / m  2 / m  2 / m
Space group I 4 / mmm (No. 139)Template: room group / 139
Lattice parameters a  = 7.0267 (4)  Å ; c  = 20.807 (2) Å
Formula units Z  = 2
Frequent crystal faces {001}, {011}, {110}
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) 3.22
Cleavage completely after {001}
Break ; Tenacity brittle
colour grass green, emerald green
Line color pale green
transparency transparent to translucent
shine Glass gloss to pearlescent
radioactivity highly radioactive
Crystal optics
Refractive indices n ω  = 1.590 to 1.592
n ε  = 1.581 to 1.582
Birefringence δ = 0.009 to 0.010
Optical character uniaxial negative
Pleochroism visible: ω = dark green to sky blue; ε = green

Torbernit , as copper uranium mica , chalcolite , Kupferautunit , Kupferphosphoruranit or out of date as Green mica or cryst Mica viridis. is a rather seldom occurring mineral from the "autunite group" within the mineral class of " phosphates , arsenates and vanadates " with the chemical composition Cu [UO 2 | PO 4 ] 2 · 12H 2 O.

Torbernite crystallizes in the tetragonal crystal system and develops mostly transparent to translucent, tabular or pyramidal crystals a few centimeters in size. It can also be found in the form of granular, earthy or massive mineral aggregates and crusty coatings. Since Torbernit often forms stacked, tabular aggregates, it can look quite similar to the Autunit , but the Autunit is a lighter, almost neon-colored yellow-green.

The color of torbernite fluctuates between different shades of green from emerald to grass and leek to more yellowish siskin and apple green, but its line color is always light green. The crystal surfaces have a glass-like shine , cleavage surfaces, on the other hand , shimmer more like mother-of-pearl and aggregate shapes are matt.

Etymology and history

Torbern Olof Bergman

Torbernite was first found in the Georg Wagsfort mine near Johanngeorgenstadt in the Saxon Ore Mountains .

The mineral is first mentioned in 1772 by Ignaz von Born in his work Lythophylacium Bornianum , where it is described as "Mica viridis crystallina, ibid." (Translated: Green crystalline mica from [Johanngeorgenstadt Sax.]; Ibid = like one over it). Abraham Gottlob Werner took up von Born's work in 1780 and described the mineral in detail, initially also referring to it as "green mica", but later as Torbernit, in honor of the Swedish chemist and mineralogist Torbern Olof Bergman .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the torbernite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "uranyl phosphates / arsenates and uranyl vanadates", where it belonged together with Autunit , Fritzscheit , Heinrichit , Kahlerite , Nováčekit , Sabugalit , Saléeit , Trögerit , Uranocircit , Uranospinit and Zeunerit the "Autunit-Gruppe" with the system no. VII / E.01 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies torbernite in the category of "uranyl phosphates and arsenates". However, this is further subdivided according to the ratio of the uranium oxide complex (UO 2 ) to the phosphate or arsenate complex (RO 4 ), so that the mineral can be found in the sub-section "UO 2  : RO 4  = 1: 1" according to its composition , where together with Autunit, Heinrichit, Kahlerit, Kirchheimerit , Metarauchit , Nováčekit-I , Nováčekit-II , Saléeit, Uranocircit I , Uranocircit II , Uranospinit, Xiangjiangit and Zeunerit it forms the unnamed group 8.EB.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns torbernite to the class of "phosphates, arsenates and vanadates", but there in the department of "water-containing phosphates etc.". Here it is together with Metatorbernit in the unnamed group 40.02a.13 within the subdivision of “Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) • x (H 2 O), with (UO 2 ) 2+ ”.

Crystal structure

Torbernite crystallizes tetragonally in the space group I 4 / mmm (space group no. 139) } with the lattice parameters a  = 7.0267 (4)  Å and c  = 20.807 (2) Å and 2 formula units per unit cell . Template: room group / 139

Packing picture of Torbernit __ U __ Cu __ O __ P __ O H2O __ H

In a study from 2003, Locock and Burns determined the crystal structures of the copper uranyl phosphates torbernite, Cu [(UO 2 ) (PO 4 )] 2 (H 2 O) 12 and metatorbernite, Cu [(UO 2 ) (PO 4 )] 2 (H 2 O) 8 with those of the copper uranyl arsenate zeunerite, Cu [(UO 2 ) (AsO 4 )] 2 (H 2 O) 12 , and metazeunerite, Cu [(UO 2 ) (AsO 4 )] 2 (H 2 O) 8 on the basis of synthetically produced single crystals. In these studies the crystal structure of torbernite could be elucidated for the first time and that of metatorbernite with regard to previous investigations (Makarov and Tobelko R 1 = 25%, Ross et al. R 1 = 9.7%, Stergiou et al. R 1 = 5.6%, Calos and Kennard R 1 = 9.2%) are made considerably more precise (Locock and Burns R 1 = 2.3%). It turns out that torbernite is isostructural to zeunerite and metatorbernite isostructural to metazeunerite. All four connections are of the autunit layer type with the [(UO 2 ) (XO 4 )] - structure motif (with X = P or As). In all these compounds, the Cu 2+ ions are surrounded by four water molecules in a square-planar manner and also coordinate the uranyl oxygen atoms, so that octahedra with Jahn-Teller distortion are formed. The crystal water molecules are held in the crystal lattice solely by hydrogen bonds .

Metatorbernit

Metatorbernite from the Margabal Mine, Entraygues-sur-Truyère , France (size: 4 cm × 3 cm × 1.8 cm)

Torbernite dehydrates easily to metatorbernite with the empirical formula Cu [UO 2 | PO 4 ] 2  · 8H 2 O. It forms as a weathering product of torbernite and can also be brought about artificially at temperatures above 75 ° C. The crystals are rather cloudy or slightly translucent with a glass luster.

Metatorbernite crystallizes tetragonal-dipyramidal in the P 4 / n (No. 85) with the lattice parameters a  = 6.9756 (5)  Å and c  = 17.349 (2) Å as well as 2 formula units per unit cell . Template: room group / 85

Packing picture of Metatorbernit __ U __ Cu __ O __ P __ O H2O __ H

The crystal structure of metatorbernite differs from that of torbernite principally in that every second uranyl phosphate layer is shifted by half the length of the a -axis in the direction [100] and [010]. The crystal structure analysis by Locock and Burns, as well as in the work by Stergiou et al., Shows that the Cu 2+ ions are only 88% occupied crystallographically. The authors therefore assume that the protonation of some crystal water molecules leads to a charge equalization, similar to what is discussed for the mineral chernikovite , so that the electrical neutrality is preserved. This is also postulated by the same authors for the Autunit . However, this hypothesis cannot be verified in practice using X-ray structure analysis methods alone.

In the structural analysis by Locock and Burns, the water of crystallization of the metatorbernite is 8 H 2 O molecules per formula unit. This agrees with the studies by Arthur Francis Hallimons and Kurt Walenta , which show that the different levels of hydration between torbernite and metatorbernite are sharply delineated and the water content of the individual compounds remains constant and does not vary, as is the case, for example, in zeolites . Therefore, empirical formulas with varying water of crystallization data for these minerals are excluded.

properties

Close-up of a pyramidal torbernite from Brest, France
(detail: 7 mm × 5 mm)
Submilimeter-sized adhesions of dipyramidal metatorbernite crystals in a druse from the Les Montmins Mine (Ste Barbe Ader), Échassières, Canton Ébreuil, Allier Department, Auvergne, France (image size: 1 mm × 1 mm)

morphology

The mineral usually occurs in the form of small, thin tablets, but it can also be flaky or powdery. More rarely, the boards can also be thicker, in which case they are reminiscent of a deck of cards. More common than these stacks are dipyramidal shapes.

physical and chemical properties

Due to its uranium content of up to 48%, torbernite is highly radioactive . Taking into account the proportions of the radioactive elements in the idealized empirical formula and the Folgezerfälle of the natural decay chains a specific activity of about 85.9 k for the mineral Bq stated / g (compared to natural potassium 0.0312 kBq / g).

In contrast to Autunit and most of the other members of the group of the same name, the mineral does not fluoresce under UV light . Torbernite is soluble in nitric acid (HNO 3 ) and before the soldering tube it melts into black spheres.

The mineral is brittle and easily fragile. Depending on the amount of crystal water contained , its Mohs hardness is 2 to 2.5 and its density is 3.22 g / cm³.

The mineral metatorbernite is formed by the loss of crystal water . The crystals become cloudy and the steps of such Torbernites become more brittle.

Education and Locations

Adhesion of kasolite (yellow radial rays) and torbernite (green tabular)

Torbernite forms as a secondary mineral in oxidation zones of uranium deposits. Accompanying minerals include autunite , metatorbernite , uraninite and zeunerite .

Around 870 sites (as of 2010) are known for Torbernit worldwide. In Germany, in addition to its type locality Johanngeorgenstadt , the mineral occurs at several other sites in the Ore Mountains as well as in the Black Forest , Fichtel Mountains , Bavarian Forest , Upper Palatinate Forest , Königsberg (Wolfstein) and Thuringian Forest . In Austria it is mainly found in the Hohe Tauern and the Fischbacher Alps . The main sites in Switzerland are the Binntal , Lavey-Morcles and Schlans .

Other locations are Argentina , Australia , Belgium , Bolivia , Brazil , Chile , China , Czech Republic , Democratic Republic of the Congo , France , Gabon , Ireland , Italy , Japan , Canada , Madagascar , Mexico , Namibia , Norway , Poland , Portugal , Romania , Slovakia , Slovenia , Spain , South Africa , Tajikistan , Uzbekistan , the United Kingdom (Great Britain) and the United States of America (USA).

use

During the Cold War , it was considered several times to mine uranium minerals such as torbernite on a large scale for the extraction of uranium as an energy resource . This was partly the case in the GDR . With the rising energy prices and the increased use of nuclear energy worldwide, the use of uranium deposits is becoming more and more attractive.

Precautions

Due to the high level of radioactivity of the mineral, samples should only be stored in dust- and radiation-tight containers, but especially never in living rooms, bedrooms or work rooms. Absorption into the body ( incorporation ) should also be prevented in any case and direct body contact should be avoided to be on the safe side and face masks and gloves should be worn when handling the mineral.

See also

literature

  • Torbernite . 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; 63 kB ; accessed on August 20, 2017]).
  • Metatorbernite . 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 August 20, 2017]).

Web links

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

Individual evidence

  1. a b c d e f g h Andrew J. Locock, Peter C. Burns: Crystal structures and synthesis of the copper-dominant members of the autunite and meta-autunite groups: torbernite, zeunerite, metatorbernite and metazeunerite . In: The Canadian Mineralogist . tape 41 , 2003, p. 489–502 ( rruff.info [PDF; 2.5 MB ; accessed on August 20, 2017]).
  2. a b Webmineral - Torbernite (English)
  3. ^ 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.  524 .
  4. a b c d Mindat - Torbernite (English)
  5. a b Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  655 (first edition: 1891).
  6. Thomas Witzke : Discovery of Torbernit at www.strahl.org
  7. ES Makarov, KI Tobelko: Crystal structure of metatorbernite . In: Doklady Akademii Nauk SSSR . tape 131 , 1960, pp. 87-89 .
  8. Malcolm Ross, HT Evans Jr., DE Appleman: Studies of the torbernite minerals. II. The crystal structure of metatorbernite . In: The American Mineralogist . tape 49 , 1964, pp. 1603–1621 ( minsocam.org [PDF; 1.1 MB ; accessed on August 20, 2017]).
  9. AC Stergiou, PJ Rentzeperis, p Sklavounos: Refinement of the crystal structure of metatorbernite . In: Journal of Crystallography . tape 205 , 1993, p. 1–7 ( rruff.info [PDF; 382 kB ; accessed on August 20, 2017]).
  10. NJ Calos, CHL Kennard: Crystal structure of copper bis (uranyl phosphate) octahydrate (metatorbernite), Cu (UO 2 PO 4 ) 2 · 8 (H 2 O) . In: Journal of Crystallography . tape 211 , 1996, pp. 701–702 , doi : 10.1524 / zkri.1996.211.10.701 ( abstract from DeGruyter [accessed on August 20, 2017]).
  11. a b AF Hallimond: The crystallography and dehydration of torbernite . In: Mineralogical Magazine . tape 17 , 1916, pp. 326–339 ( minersoc.org [PDF; 546 kB ; accessed on August 20, 2017]).
  12. Mindat - Metatorbernite (English)
  13. Andrew J. Locock, Peter C. Burns: The crystal structure of synthetic autunite, Ca [(UO 2 ) (PO 4 )] 2 (H 2 O) 11 . In: American Mineralogist . tape 88 , 2003, p. 240–244 ( rruff.info [PDF; 398 kB ]).
  14. ^ AF Hallimond: Meta-torbernite I. Its physical properties and relation to torbernite . In: Mineralogical Magazine . tape 19 , 1920, p. 43–47 ( minersoc.org [PDF; 222 kB ; accessed on August 20, 2017]).
  15. Kurt Walenta: Contributions to the knowledge of rare arsenate minerals with special consideration of occurrences of the Black Forest . In: Tschermaks mineralogical and petrographic communications . tape 9 , no. 3 , 1964, pp. 252-282 , doi : 10.1007 / BF01128088 .
  16. Mindat - Number of localities for torbernite
  17. Find location list for torbernite at the Mineralienatlas and at Mindat