Francevillite
- Ba ( UO2 ) 2 ( VO4 ) 2.5 H2O
- (Ba, Pb) [ UO2 | VO4 ] 2.5 H2O
Francevillite is a rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the idealized chemical composition Ba ( UO2 ) 2 ( VO4 ) 2.5 H2O, is therefore a barium uranyl vanadate. However, since in naturally occurring Francevillite usually a small fraction of barium replaced by lead ( substituted ), the formula is often also with (Ba, Pb) [ UO2 | VO4 ] indicated 2.5 H2O.
Francevillite is translucent and developed only small crystals usually orange -yellow to yellow-green mineral aggregates and often adhesions rhombic single crystals.
Special Features
The mineral is classified radioactive due to its uranium content of up to 48% as very strong and has a specific activity of about 87 kBq / g (compared to natural potassium 0.0312 kBq / g).
Francevillite may vary by locality contain less lead in its structure, which occupies the places of barium in the crystal lattice or more. Francevillite therefore also forms a complete solid solution series with its lead analogue Curienit (Pb (UO2 ) 2 ( V2O8 ) · 5H2O).
Etymology and history
Francevillite was first discovered in the " Mounana Mine" in Franceville in Gabon and described in 1957, designated by Georges industry, Marie- Edith Ropert, Francis Chantret, Bernard Morignat and Robert Pouget the mineral after its place of origin.
Type material of the mineral is stored in the Mines ParisTech in Paris and at the Natural History Museum in London.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Francevillite belonged to the mineral class of " phosphates, arsenates and vanadates " and then to the Department of " Uranylphosphate / arsenates and Uranylvanadate " where he along with carnotite, Curienit, Margaritasit, Metatyuyamunit, Metavanuralit, Sengierit, Strelkinit, Tyuyamunite and Vanuralit the group of " uranyl Gruppenvanadate with [ UO2 ] 2 - [ V2O8 ] 6 - " with the system no. VII/E.11 formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of Strunz 's Mineral classification assigns the Francevillite other hand, in the class of " oxides and hydroxides " and there in the department of " V [ 5,6] vanadates, " a. This is also further divided according to the crystal structure, so that the mineral is found in accordance with its construction in the subsection " uranyl Gruppenvanadate ( Sorovanadate ) ", where he was named the " Francevillitgruppe " with the system no. Forms 4.HB.15 and the other members Curienit and Fritz log.
The mostly commonly used in English-speaking classification of minerals according to Dana assigns the Francevillite as the outdated Strunz'sche systematics in the class of " phosphates, arsenates and vanadates " one -up, but in the department of " water -containing phosphates, etc. ". Here he is with the Curienit in the unnamed group 40.02a.27 within the sub-division of " water -containing phosphates, etc., with A2 ( B2 ) 2 ( XO4 ) × x (H2O), with (UO2 ) 2 " to find.
Education and Locations
Francevillite formed in the oxidation zone of lead-containing uranium - vanadium deposits. Accompanying minerals can occur, among other carnotite, Chervetit, Curienit, Dewindtit, Duttonit, Johannit, Kasolit, Mottramite, Torbernite, Uranopilite and Vanuralit.
A rare mineral formation Francevillite could be detected only in a few localities, where so far (as of 2013) are about 30 localities known as. Apart from its type locality " Mounana Mine" the mineral nor entered Gabon in some other mines in the area of Franceville evident. This location is also renowned for its well-trained crystals and aggregates.
In Germany you know Francevillite in part from the Clara mine in Oberwolfach in Baden- Württemberg, the quarry steel at Dörrmorsbach in Bavaria, the uranium deposit Schweisweiler - Winnweiler in Rhineland -Palatinate and from Tirpersdorf in Saxony.
Other previously known localities are the " Sleisbeck Mine" in the Northern Territory of Australia, several pits in the French regions of Auvergne and Midi- Pyrénées, the uranium deposit in the Otish Mountains near the James Bay ( Baie- James ) in Canada, Karamurun the river Ili in Kazakhstan, Tyuya - Muyun the Altay Mountains in Kyrgyzstan, several pits at Kambove and Kolwezi in the Katanga province of the Democratic Republic of Congo, the Moron massif of Aldanhochlandes ( Eastern Siberia ) and the Zaonezhie peninsula on Lake Onega ( Republic of Karelia ) in Russia, Todraž in Slovenia, Litice Orlicí in the Czech region of Bohemia, St Stephen in Brannel in the English county of Cornwall in the United Kingdom and Packerton Junction in Carbon County (Pennsylvania ) and the " Pandora Mine" in San Juan County (Utah ) in the United States of America.
Crystal structure
Francevillite crystallizes in the orthorhombic space group PCAN ( Raumgruppen-Nr. 60) with the lattice parameters a = 10.42 Å; b = 8.51 Å and c = 16.76 Å and four formula units per unit cell.
It thereby formed layers of UO2 - V2O8 units that are linked by the barium atoms with each other. Two vanadium atoms constitute two edge-sharing pyramids whose vertices occupy oxygen atoms. The two pyramid tips look here in opposite directions and coordinate the barium atoms. The remaining free edges of the vanadate polyhedra coordinate the uranyl equatorial units. A uranyl oxygen atom also is coordinating a barium atom, the second remains uncoordinated. The barium atoms have a distorted tetrahedral geometry.
Security measures
When dealing with Francevillite is to ensure adequate radiation protection. To prevent incorporation ( uptake into the body ), is thorough hand washing after handling with bare hands is recommended.