Vandendriesscheit
| Vandendriesscheit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Pb 1.57 [(UO 2 ) 10 | O 6 | (OH) 11 ] • 11H 2 O |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.GB.40 ( 8th edition : IV / H.07) 08/05/01/01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | mmm |
| Space group | Pbca (No. 61) |
| Lattice parameters |
a = 14.117 Å ; b = 41.378 Å; c = 14.535 Å α = 90 °; β = 90 °; γ = 90 ° |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | 5.45 |
| Cleavage | completely after {001} |
| colour | brown-yellow, yellow-orange |
| Line color | Please complete |
| transparency | transparent to translucent |
| shine | Diamond luster |
| radioactivity | very strong |
| Crystal optics | |
| Refractive indices |
n α = 1.780 n β = 1.850 n γ = 1.860 |
| Birefringence | δ = 0.080 |
| Optical character | biaxial negative |
| Axis angle | 2V = measured: 60 °; calculated: 40 ° |
| Pleochroism | X = almost colorless, Y = Z = yellow-orange to golden yellow |
Vandendriesscheit is a rather rarely occurring lead-containing uranium mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition Pb 1.57 [(UO 2 ) 10 | O 6 | (OH) 11 ] · 11H 2 O and develops mostly transparent to translucent crystals of brown-yellow to yellow-orange color.
Etymology and history
Vandendriesscheit was first described in 1947 by the Belgian mineralogist Johannes Franciscus Vaes together with the minerals billietite , masuyit , richetite , studtite and diderichite on a sample from the Shinkolobwe mine , who made it in honor of the Belgian geologist Adrien Vandendriessche (January 13, 1914 to 27. May 1940) who dealt with Congolese minerals. In 1997 the single crystal structure analysis of a Vandendriesscheit sample from the Shinkolobwe mine in the Democratic Republic of the Congo was successful .
The Vandendriesscheit type mineral is located at Harvard University (catalog no. 106523) in Cambridge , Massachusetts , USA .
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Vandendriesscheit belonged to the mineral class of "oxides and hydroxides" and there to the department of "uranyl hydroxides and hydrates", where it together with Curit , Fourmarierit , Metavandendriesscheit , Richetit , Sayrit and Spriggit forms an independent group.
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 the Vandendriesscheit to the class of "oxides and hydroxides" and there in the department of "uranyl hydroxides". However, this section is further subdivided according to the presence of further cations and the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “With additional cations ( K , Ca , Ba , Pb etc.); with predominantly UO 2 (O, OH) 5 pentagonal polyhedra ”can be found under together with Metavandendriesscheit in the Vandendriesscheitgruppe .
The systematics of minerals according to Dana also assigns the Vandendriesscheit to the class of "oxides and hydroxides", but there in the department of "uranium and thorium-containing oxides". Here it is with the system no. 05.08.01.01 within the sub-section of the “ 05.08 Oxides with uranium and thorium and a cation charge of 6+, which contain Pb and considerable amounts of crystal water ”.
Crystal structure
Vandendriesscheit crystallizes in the orthorhombic crystal system in the space group Pbca (space group no. 61) with the lattice parameters a = 14.117 Å , b = 41.378 Å, c = 14.535 Å and α = β = γ = 90 ° as well as eight formula units per unit cell .
In the crystal structure , the uranium atom has a pentagonal-bipyramidal geometry. The peaks of the pyramid represent the uranyl oxygen atoms, in the equatorial plane oxide or hydroxide ions are coordinated to the uranium atom. There are two different lead positions, one of which is only 57% occupied, which makes up 1.57 lead atoms in the empirical formula. There are 11 water molecules in the structure, five of which are coordinated to the lead atoms. The remaining water molecules are only held in the structure by hydrogen bonds. A network of equatorial edge-linked uranyl units is created, whereby these are coordinated by the lead ions via the uranyl oxygen atoms in such a way that parallel layers are created. This motif is one of the most complex among the uranyl oxide hydrates. The crystal structure of the Vandendriesscheit in this form is very similar to the structures of Schoepit and Becquerelit .
properties
The mineral is very radioactive due to its uranium content of up to 67.8 % by weight . 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 121.3 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.
Modifications and varieties
X-ray crystallographic investigations on Vandendriesscheit crystals have shown that, in addition to the Vandendriesscheit (= phase I ), a second phase can be found that does not differ optically from the first. This second phase was called " Metavandendriesscheit ". The prefix “Meta-” indicates the loss of water of crystallization , which could be proven by storing a clear orange crystal of Vandendriesscheit over concentrated sulfuric acid . Due to the dehydrating effect of sulfuric acid, the crystal became cloudy, so that the diffraction pattern showed phase II (metavandendriac wood) as the main component. This behavior is very similar to that of Schoepit .
Education and Locations
Vandendriesscheit is found as a conversion product of Precambrian primary uranium deposits. The washing out of mobile UO 2 2+ ions leads to a relative enrichment of lead ions, so that lead-rich uranium oxide hydrates are formed. Depending on where it was found, the mineral is associated with other uranium minerals and occurs in Shinkolobwe with metavandendriesscheit , fourmarierite , rutherfordin , becquerelite , metatorbernite and uraninite, among others .
In Germany, Vandendriesscheit was found in Menzenschwand , Wittichen and Oelsnitz , among others . In Switzerland it can be found in the canton of Valais in Les Marécottes and Isérables, and in Austria in Hüttwinkl.
Other sites in France are the Occitania region in the Hérault department in Rabejac near Lodève and the Rhône-Alpes region . It is also known from a few sources in Argentina , Australia , China , the Czech Republic , Italy , Norway , Spain , Sweden , Tanzania , the United Kingdom and the United States of America .
Precautions
Due to the strong radioactivity of the mineral, mineral samples from Vandendriesscheit should only be kept in dust- and radiation-tight containers, but above all never in living rooms, bedrooms or work rooms. Likewise, because of the high toxicity and radioactivity of uranyl compounds, absorption into the body ( incorporation , ingestion ) should be prevented in any case and, for safety, direct body contact should be avoided and face masks and gloves should be worn when handling the mineral.
See also
literature
- Vandendriesscheite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 71.0 kB ).
Web links
Individual evidence
- ↑ a b c d e f g h PC Burns: A new uranyl oxide hydrate sheet in vandendriesscheite: Implications for mineral paragenesis and the corrosion of spent nuclear fuel. In: American Mineralogist, 1997, 82, pp. 1176–1186 ( PDF (English) 1.5 MB ).
- ↑ a b c Vandendriesscheit at Webmineral.com
- ↑ a b c Vandendriesscheite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( PDF 73.0 kB ).
- ↑ a b - Vandendriesscheit at Mindat.org
- ^ JF Vaes: Six nouveaux minéraux d'urane provenant de Shinkolobwe (Katanga) . In: Annales de la Société Géologique de Belgique. 1947, pp. B212 – B226 ( PDF (French) 441 kB ).
- ↑ M. Fleischer: New mineral names . In: American Mineralogist . 1948, 33, pp. 384-386 ( PDF (English) 176 kB ).
- ^ CL Christ, Joan R. Clark: Crystal Chemical Studies Of Some Uranyl Oxide Minerals . In: The American Mineralogist. 1960, 45, 1026-1061 PDF (English) 2.1 MB