Compreignacit
| Compreignacit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | K 2 [(UO 2 ) 6 | O 4 | (OH) 6 ] • 7H 2 O |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.GB.05 ( 8th edition : IV / H.03) 07/05/01/01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; mmm |
| Room group (no.) | Pnmn (No. 58) |
| Lattice parameters |
a = 14.859 Å ; b = 7.175 Å; c = 12.187 Å α = 90 °; β = 90 °; γ = 90 ° |
| Formula units | Z = 2 |
| Frequent crystal faces | flattened to {001}; large {001} and {010} |
| Twinning | often twinned to {110}, as simple contact twins, or twinned in various ways |
| Physical Properties | |
| Mohs hardness | Please complete |
| Density (g / cm 3 ) | measured: 5.03 (5); calculated: 5.13 (5) |
| Cleavage | completely after {001} |
| Break ; Tenacity | brittle |
| colour | yellow, golden yellow, light yellow |
| Line color | pale yellow |
| transparency | transparent to translucent |
| shine | Please complete |
| radioactivity | very strong |
| Crystal optics | |
| Refractive indices |
n α = 1.790 n β = 1.798 n γ = 1.802 |
| Birefringence | δ = 0.012 |
| Optical character | biaxial negative |
| Axis angle | 2V = measured: 13 ° |
| Pleochroism | intense: X = colorless; Y = Z = yellow |
Compreignacit is a very rarely occurring uranium mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition K 2 [(UO 2 ) 6 | O 4 | (OH) 6 ] · 7H 2 O and very small, at most 0.1 mm large, mostly translucent, often twinned crystals of bright yellow Colour.
Etymology and history
Compreignacit was first found in 1964 in the Margnac mine in the Haute-Vienne department , Limousin region in France and named after the place Compreignac , which is located near the mine.
The type mineral is located at the Pierre and Marie Curie University in Paris; at Mines ParisTech in Paris, France, and at the National Museum of Natural History in Washington, DC, USA.
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Compreignacit belonged to the mineral class of "oxides and hydroxides" and there to the department of "uranyl hydroxides and hydrates", where together with Becquerelit , Billietit , Masuyit and Protasit 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 Compreignacit 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 in the Compreignacite group together with Agrinierite and Rameauit .
The systematics of minerals according to Dana also assigns the Compreignacit to the class of "oxides and hydroxides", but there in the department of "uranium and thorium-containing oxides". Here it can be found within the subdivision of “ 05.07 Oxides containing uranium and thorium with alkali or hydrated hydroxide components ” in the Becquerelite group together with Becquerelite and Billietite .
Crystal structure
Compreignacite crystallizes in the orthorhombic crystal system in the space group Pnmn with the lattice parameters a = 14.859 Å , b = 7.175 Å, c = 12.187 Å and α = β = γ = = 90 ° as well as two formula units per unit cell . The following figures show the structure of the Compreignacit unit cell:
In the crystal structure , the uranyl units are coordinated by two oxygen atoms and three hydroxide ions, so that layers of edge-sharing pentagonal-bipyramidal coordination polyhedra arise. These layers are topologically identical to α-U 3 O 8 , becquerelite , billietite , protasite and richetite . These layers are linked by potassium ions. In his crystal structure analysis, Peter Burns postulates that the potassium ions in the structure of compreignacite could theoretically be replaced relatively easily by cesium ions, since the sums of the effective ion radii change from Cs + ··· O 2− to K + ··· O 2− only differ by 9%. An experimental verification of this thesis is still pending, but could be of relevance for investigations into nuclear waste, since radioactive 137 Cs could be bound in Compreignacite structures.
properties
The mineral is very radioactive due to its uranium content of up to 71.1 % by weight . Taking into account the proportions of radioactive elements in the idealized empirical formula as well as the subsequent decays of the natural decay series, a specific activity of about 127.3 k Bq / g is specified for the mineral (for comparison: natural potassium 0.0312 kBq / g). However, the quoted value can vary significantly depending on the mineral content and composition of the levels; selective enrichment or depletion of the radioactive decay products are also possible and change the activity.
Education and Locations
Compreignacite is found as a very rare transformation product in the oxidation zone of primary uranium ore deposits. In its type locality, the Margnac Mine in France, the mineral is associated with uraninite , cuprosklodovskite , uranophane , zeunerite , schoepite , brochantite , connellite and agardite (Ce) . Parageneses with cuprosklodovskite, uranophane, brochantite, connellite, calcite , chalcopyrite , siderite , uraninite and potassium feldspar are found in the Wheal Edward Mine in Cornwall, England .
In Germany, Compreignacit was only found in the Krunkelbach mine near Menzenschwand and in the Lichtenberg mine near Ronneburg .
Other locations for are Finhaut and Les Marécottes in Switzerland as well as Příbram , Horní Slavkov , Jáchymov and Slavkovice in the Czech Republic , the Eureka mine in Spain , Lombardy and Sardinia in Italy and in Colorado, New Hampshire and Utah in the USA .
Precautions
Due to the high level of radioactivity of the mineral, mineral samples from Compreignacit should only be kept in dust- and radiation-proof containers, but above all never in living rooms, bedrooms or workrooms. 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
- Compreignacite , 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 ).
Web links
Individual evidence
- ↑ a b c d e f PC Burns: "The structure of Compreignacite, K 2 [(UO 2 ) 6 | O 4 | (OH) 6 ] · 7H 2 O" In: "The Canadian Mineralogist" 1998, 36, 1061 -1067 ( PDF (English) 543 kB ).
- ↑ a b c Compreignacit at Webmineral.com .
- ↑ a b c Compreignacite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 71.2 kB ).
- ↑ a b Mindat - Compreignacit at Mindat.org .
- ↑ M. Fleischer: "New mineral names", In: "American Mineralogist" 1965, 50, 805–813 ( PDF (English) 532 kB ).