Johannit

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Johannit
Johannite-ea9b.jpg
Johannit from the Malwine shaft, Annaberg-Buchholz , Ore Mountains ( overall size : 3.5 cm × 2 cm × 1.7 cm)
General and classification
other names

Uranium vitriol

chemical formula Cu [UO 2 | OH | SO 4 ] 2 · 8H 2 O
Mineral class
(and possibly department) 		Sulfates
System no. to Strunz
and to Dana 		7.EB.05 ( 8th edition : VI / D.21)
08/31/02/01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Room group (no.) P 1 (No. 2)
Lattice parameters a  = 8.90  Å ; b  = 9.50 Å; c  = 6.81 Å,
α  = 109.9 °; β  = 112.0 °; γ  = 100.4 °
Formula units Z  = 1
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) measured: 3.32; calculated: 3.44
Cleavage good after {100}
colour grass green, emerald green
Line color light green
transparency transparent to translucent
shine Glass gloss
radioactivity very strong
Crystal optics
Refractive indices n α  = 1.572 to 1.577
n β  = 1.592 to 1.597
n γ  = 1.612 to 1.616
Birefringence δ = 0.040
Optical character alternating biaxially
Axis angle 2V = 90 ° (calculated: 86 to 88 °)
Pleochroism strong: X = colorless; Y = light yellow; Z = greenish or canary yellow

Johannite , also known as uranium vitriol , is a rarely occurring mineral from the mineral class of sulfates . It crystallizes in the triclinic crystal system with the chemical composition Cu [UO 2 | OH | SO 4 ] 2 · 8 H 2 O and is therefore chemically seen a hydrous basic copper - uranyl - sulfate .

Johannit develops only small, prismatic to thick tabular crystals , but mostly scaly or kidney-shaped aggregates and crusty coatings of grass-green to emerald-green color with light green streak color .

Etymology and history

Johannite was first discovered in the Elias mine near Jáchymov (German Sankt Joachimsthal ) in Okres Karlovy Vary (German Karlsbad ) in the Czech Republic and described in 1830 by Haidinger , who named the mineral after Archduke Johann von Österreich (1782-1859), the founder of the Styrian State Museum Joanneum (Austria), named.

The type material of the mineral is kept in the Natural History Museum Vienna (catalog no. Aa186).

classification

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the Johannit belonged to the mineral class of "sulfates, chromates, molybdates, wolframates (including some selenates and tellurates)" and there to the department of "water-containing sulfates with foreign anions ", where he named the "Johannit Group" with the system no. VI / D.21 and the other members Deliensit , Pseudojohannit and Schröckingerit formed.

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 assigns Johannit to the class of "sulfates (and relatives)", although there it is in the "uranyl sulfates" category. This is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With medium-sized cations”, where it is the only member of the unnamed group 7.EB.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Johannit to the class of "sulfates, chromates and molybdates" and there in the category of "water-containing sulfates with hydroxyl or halogen". Here it can be found together with Deliensit in the unnamed group 08/31/02 within the subsection “ Hydrogen sulphates with hydroxyl or halogen with (A + B 2+ ) 3 (XO 4 ) 2 Z q × x (H 2 O)”.

Crystal structure

Johannite crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 8.90  Å ; b  = 9.50 Å; c  = 6.81 Å; α = 109.9 °; β = 112.0 ° and γ = 100.4 ° with one formula unit per unit cell .

properties

The mineral is radioactive due to its uranium content of up to 48.9% . 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 87.5 k for the mineral Bq stated / g (compared to natural potassium 0.0312 kBq / g). The quoted value can vary significantly depending on the mineral content and the composition of the levels; selective enrichment or depletion of the radioactive decay products is also possible and changes the activity. Due to the natural isotopic composition of uranium, this corresponds to an equivalent dose of 12.4 µ Sv / h per gram of the mineral.

Education and Locations

Johannit from Ronneburg in Thuringia

Johannite is formed as a secondary mineral by oxidation from uraninite together with various other uranium minerals .

As a rare mineral formation, Johannite could only be detected at a few sites, whereby so far (as of 2014) around 70 sites are known. In addition to its type locality Elias Mine and the nearby mines Svornost and Rovnost near Jáchymov ( Sankt Joachimsthal ), the mineral was also found in the Czech Republic near Předbořice in Central Bohemia and near Újezd ​​u Kasejovic ( Kasejovice ) in the Pilsen region.

In Germany, Johannit was found in the Krunkelbach mine near the municipality of Menzenschwand in Baden-Württemberg, the Johannesschacht mine near Wölsendorf in Bavaria, in the Malwine mine at Schreckenberg , near Johanngeorgenstadt , in Schneeberg and in the Pöhla- Tellerhäuser mine in the Saxon Ore Mountains as well as at Paitzdorf in the Thuringian district of Greiz.

The only known site in Switzerland to date is the La Creusaz uranium prospection near Les Marécottes in the Trient Valley in the canton of Valais.

Other sites are in Argentina, Australia, France, Gabon, Greece, Italy, Slovenia, England in the United Kingdom (UK) and in several states of the USA.

Precautions

Due to the toxicity and the strong radioactivity of the mineral, mineral samples from Johannit should only be kept in dust- and radiation-proof containers, but especially never in living rooms, bedrooms or workrooms. Absorption into the body (incorporation, ingestion ) should also be prevented in any case and, for safety, direct body contact should be avoided and respiratory protection mask and gloves should be worn when handling the mineral .

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e 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.  414 .
  2. ↑ a b c Webmineral - Johannite (English)
  3. ↑ a b c Johannite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 68 kB )
  4. ↑ a b c d Mindat - Johannite (English)
  5. ^ Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 597 .
  6. ↑ Mindat - Number of localities for Johannit
  7. ↑ Find location list for rathite at the Mineralienatlas and at Mindat