Metakirchheimerite
| Metakirchheimerite | |
|---|---|
| General and classification | |
| chemical formula | Co [UO 2 | AsO 4 ] 2 • 8H 2 O |
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8.EB.10 ( 8th edition : VII / E.02) 40.02a.17.01 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetrahedral - dipyramidal 4 / m 2 / m 2 / m |
| Room group (no.) | P 4 2 / n (No. 86) |
| Lattice parameters | a = 7.15 Å ; c = 8.62 Å |
| Formula units | Z = 1 |
| Physical Properties | |
| Mohs hardness | 2 to 2.5 |
| Density (g / cm 3 ) | measured: 3.33; calculated: [4.11] |
| Cleavage | perfect after {001}, good after {100} |
| colour | light pink to flesh pink |
| Line color | White |
| transparency | Please complete |
| shine | Pearlescent luster on the cleavage surface {001} |
| radioactivity | very radioactive |
| Crystal optics | |
| Refractive indices |
n ω = 1.644 n ε = 1.617 |
| Birefringence | δ = 0.027 |
| Optical character | uniaxial negative (also abnormally biaxial negative) |
| Axis angle | 2V = 0 to 20 ° |
Metakirchheimerite (also Meta-Kirchheimerite ) is a very rare mineral from the mineral class of " phosphates , arsenates and vanadates ", which belongs to the group of uranium mica . It crystallizes in the tetragonal crystal system with the chemical composition Co [UO 2 | AsO 4 ] 2 • 8H 2 O and has so far only been found in the form of tabular crystals with a square habit up to about 50 μm in size from light pink to flesh pink in color.
Metakirchheimerite is sometimes also referred to as Kirchheimerite for short . However, this is also the name for the water-containing form of metakirchheimerite with the composition Co [UO 2 | AsO 4 ] 2 • 12H 2 O, which has not been observed in nature up to now .
Etymology and history
Kirchheimerite was first discovered in the Sophia mine near Wittichen in the Black Forest district of Rottweil in Baden-Württemberg and described in 1958 by Kurt Walenta , who named the mineral after the then President of the Baden-Württemberg Geological Office , Professor Franz Kirchheimer .
During his analyzes of metakirchheimerite, Walenta was able to prove through experiments that Kirchheimerite, after its formation in nature, changes very quickly to metakirchheimerite through water loss ( dehydration ) and has therefore only been found in this form so far. However, this conversion is relatively easy to reverse. After just one day of storage of natural metakirchheimerite in a cold, wet atmosphere, it converts back to the higher hydration level. According to Walenta, it should therefore be possible to find natural Kirchheimerite, at least in the cold season.
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the metakirchheimerite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "uranyl phosphates and uranyl vanadates", where together with abernathyite , bassetite , chernikovite , lehnerite , meta-Ankoleit , meta-autunite , Metaheinrichit , Metakahlerit , Metalodèvit , Metanováčekit , Metatorbernit , Metauranocircit , Metauranospinit , Metazeunerit , sodium meta-autunite , Natrouranospinit , pseudo-autunite , Ulrichit and Uramphit formed a distinct group.
The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also assigns metakirchheimerite to the class of "phosphates, arsenates and vanadates" and there in the department of "uranyl phosphates and arsenates". However, this section is further subdivided according to the ratio of uranium oxide complex (UO 2 ) to phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral according to its composition is in the sub-section "UO 2 : RO 4 = 1: 1" is to find where it along with Bassetit, Lehnerit, meta-autunite, Metaheinrichit, Metakahlerit, Metalodèvit, Metanováčekit, Metasaléeit , Metatorbernit, Metauramphit , Metauranocircit-I , Metauranocircit II , Metauranospinit, Metazeunerit, Przhevalskit and Uramarsit the "meta-autunite -Group "with the system no. 8.EB.10 forms. The hypothetical mineral Kirchheimerite is in the same subdivision in the "Autunit group" with the system no. 8.EB.05 sorted.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the metakirchheimerite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here it is together with Metarauchit in the unnamed group 40.02a.17 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
Metakirchheimerite crystallizes tetragonally in the space group P 4 2 / n (space group no. 86) with the lattice parameters a = 7.15 Å and c = 8.62 Å and one formula unit per unit cell .
properties
The mineral is toxic due to its arsenic content of around 17.7% and classified as very highly radioactive due to its uranium content of up to 46.6% and has a specific activity of around 83.5 k Bq / g (for comparison: natural potassium 31.2 Bq / g).
Its mostly pale pink color is very unusual for radioactive minerals and therefore, like its non-existent fluorescence, quite noticeable.
Education and Locations
Metakirchheimerit forms like other uranium mica in the oxidation zone of uranium - deposits . In the hydrothermal Co - U - Ag - Bi - As - transitions occurs Kirchheimerit together with Kahlerit as scaly crusty secondary conversion product primary uranium minerals such. B. uraninite . Other accompanying minerals include Nováčekit , Metaheinrichit and Erythrin .
Metakirchheimerite, a very rare mineral, has so far only been found in a few locations (registered locations at mindat.org: 7). In addition to its type locality Grube Sophia near Wittichen, which is now closed, the mineral was found in Germany in the nearby pits “St.- Josephs-Zeche ”and“ Anton ”.
In the Czech Republic, Metakirchheimerit was found in the Jáchymov " Grube Einigkeit " ( Důl Svornost ) and in the local vein "Jan Evangelista". The French site Riviéral near Lodève in the Languedoc-Roussillon region is still questionable.
Precautions
Due to the toxicity and 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 workrooms. 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
Individual evidence
- ↑ a b c d e 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. 525 .
- ↑ a b Webmineral - Metakirchheimerite (English)
- ↑ a b Handbook of Mineralogy - Metakirchheimerite (English, PDF 63.5 kB)
- ↑ a b c Metakirchheimerite at mindat.org (engl.)
- ^ Kurt Walenta: Contributions to the knowledge of rare arsenate minerals with special consideration of occurrences of the Black Forest , pp. 160–161
- ↑ Mindat - number of sites for Metakirchheimerite (last accessed on August 19, 2011)
literature
- Kurt Walenta: Contributions to the knowledge of rare arsenate minerals with special consideration of occurrences of the Black Forest , in: Mineralogy and Petrology , 1962, Volume 9, Numbers 1–2, 111–174, doi : 10.1007 / BF01127780
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, Stuttgart 1978, ISBN 3-432-82986-8 , p. 654-655 .
- Strübel G. & Zimmer SH (1991): Lexicon of Minerals. Enke publishing house, Stuttgart. ISBN 3-432-92722-3