Francevillit
| Francevillit | |
|---|---|
 |
|
| General and classification | |
| chemical formula |
|
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.HB.15 ( 8th edition : VII / E.11) 40.02a.27.01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Space group | Pcan (No. 60, position 3) |
| Lattice parameters | a = 10.42 Å ; b = 8.51 Å; c = 16.76 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | measured: 4.55; calculated: [4.56] |
| Cleavage | completely after {001} |
| colour | lemon yellow, yellow orange, orange, greenish yellow, green, brown |
| Line color | light yellow |
| transparency | translucent |
| shine | Diamond luster, pearlescent luster |
| radioactivity | very strong |
| Crystal optics | |
| Refractive indices |
n α = 1.750 to 1.785 n β = 1.910 to 1.952 n γ = 1.945 to 2.002 |
| Birefringence | δ = 0.195 to 0.217 |
| Optical character | biaxial negative |
| Axis angle | 2V = measured: 52 °; calculated: 46 to 52 ° |
| Pleochroism | X = colorless; Y, Z = yellow |
Francevillit 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 (UO 2 ) 2 (VO 4 ) 2 · 5H 2 O, that is a barium - uranyl vanadate.
However, since a small proportion of barium is usually replaced ( substituted ) by lead in naturally occurring Francevillit , the formula is often also given with (Ba, Pb) [UO 2 | VO 4 ] 2 · 5H 2 O. The less lead is contained in its structure, the greener the color appears and with increasing lead content the color tends towards orange.
Francevillit is translucent and develops only small crystals usually orange-yellow to yellow-green mineral aggregates and often adhesions rhombic single crystals .
Etymology and history
Francevillit was first discovered in the "Mounana Mine" near Franceville in Gabon and described in 1957 by Georges Branche, Marie-Edith Ropert, Francis Chantret, Bernard Morignat and Robert Pouget, who named the mineral after its place of origin.
Type material of the mineral is kept at the Mines ParisTech in Paris and in the Natural History Museum (catalog number 1958,597) in London .
classification
In the 8th edition of the mineral classification according to Strunz , which is now outdated, but still in use , Francevillit belonged to the mineral class of " phosphates , arsenates and vanadates " and there to the department of "uranyl phosphates / arsenates and uranyl vanadates ", where it belongs together with carnotite , curienite , margaritasite , Metatyuyamunit , Metavanuralit , Sengierit , Strelkinit , Tyuyamunit and Vanuralit the group of the "uranyl group vanadates with [UO 2 ] 2+ - [V 2 O 8 ] 6− " with the system no. VII / E.11 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), assigns the Francevillit to the class of "oxides and hydroxides" and there in the department of "V [5,6] vanadates" . This is also further subdivided according to the crystal structure, so that the mineral can be found in the sub-section "Uranyl group vanadate (Sorovanadate)" according to its structure, where it is named after the "Francevillit group" with the system no. 4.HB.15 and the other members Curienit and Fritzscheit .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Francevillit to the class of "phosphates, arsenates and vanadates", like the outdated Strunz'sche systematics, but there in the department of "water-containing phosphates etc." Here it is together with the curienite in the unnamed group 40.02a.27 within the subdivision of “Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O), with (UO 2 ) 2+ ”to be found.
Crystal structure
Francevillit crystallizes orthorhombically in the space group Pcan (space group no. 60, position 3) with the lattice parameters a = 10.42 Å ; b = 8.51 Å and c = 16.76 Å as well as 4 formula units per unit cell .
Layers of UO 2 -V 2 O 8 units are formed, which are linked to one another by the barium atoms. Two vanadium atoms form two edge-linked pyramids, the corners of which are occupied by oxygen atoms . The two pyramid tips look in opposite directions and coordinate the barium atoms. The other free edges of the vanadate polyhedra coordinate the uranyl units equatorially. A uranyl oxygen atom also coordinates a barium atom, the second remains uncoordinated. The barium atoms have a distorted tetrahedral geometry.
properties
The mineral is very strong by its uranium content of up to 48% radioactively classified and has a specific activity of about 87 k Bq / g (compared to natural potassium 0.0312 kBq / g).
Depending on where it was found, Francevillit may contain more or less lead in its structure, which occupies the places of the barium in the crystal lattice . Francevillit therefore also forms a complete mixed crystal row with its lead analogue curienite (Pb (UO 2 ) 2 (V 2 O 8 ) · 5H 2 O).
Education and Locations
Francevillit forms in the oxidation zone of lead-containing uranium-vanadium deposits . As accompanying minerals may include Carnotit , Chervetit , Curienit , Dewindtit , Duttonit , Johannit , Kasolite , Mottramit , Torbernit , Uranopilite and Vanuralit occur.
As a rare mineral formation, Francevillit could only be detected at a few sites, whereby so far (as of 2013) around 30 sites are known. In addition to its type locality "Mounana Mine", the mineral appeared in Gabon in several other pits in the vicinity of Franceville . This site is also known for its particularly well-developed crystals and aggregates.
In Germany, Francevillit is known from the Clara mine near Oberwolfach in Baden-Württemberg, the steel quarry near Dörrmorsbach in Bavaria, the Schweisweiler - Winnweiler uranium deposit in Rhineland-Palatinate and from Tirpersdorf in Saxony.
Other previously known sites are the “Sleisbeck Mine” in the Northern Territory of Australia, several pits in the French regions of Auvergne-Rhône-Alpes and Occitania , the uranium deposit in the Otish Mountains near James Bay (Baie-James) in Canada, Karamurun am Ili River in Kazakhstan, Tyuya-Muyun in the Alai Mountains in Kyrgyzstan, several pits near Kambove and Kolwezi in the Katanga Province of the Democratic Republic of Congo, the Murun Massif of the Aldan Highlands (Eastern Siberia) and the Zaonezhie Peninsula on Lake Onega (Republic of Karelia) in Russia, Todraž in Slovenia, Litice nad Orlicí in the Czech region of Bohemia , St Stephen in Brannel in the English county of Cornwall in the United Kingdom as well as Packerton Junction in Carbon County (Pennsylvania) and the "Pandora Mine" in San Juan County (Utah) in the United States of America.
Precautions
Due to the toxicity and radioactivity of the mineral, mineral samples from Francevillit should only be kept in dust-proof 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
- G. Branche, ME Ropert, F. Chantret, B. Morignat, R. Pouget: La francevillite, nouveau minéral uranifère , In: Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences , Volume 245 (1957), p. 89– 91
- M. Fleischer: New mineral names , In: American Mineralogist , Volume 43 (1958), pp. 180–180 ( PDF 72.5 kB ; Francevillite p. 1)
- Francevillite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 65.7 kB )
Web links
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names; February 2013 (PDF 1.3 MB; Francevillite p. 59)
- ↑ 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. 256 .
- ↑ a b Webmineral - Francevillite (English)
- ↑ a b Francevillite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 65.7 kB )
- ↑ a b c Mindat - Francevillite (English)
- ↑ Fabien P. Cesbron et Pierre Bariand, "The Uranium-Vanadium Deposit of Mounana, Gabon", Mineralogical Record, vol. 6, no 5, 1975, pp. 237-249
- ↑ K. Mereiter: Crystal structure refinement of two francevillites, (Ba, Pb) (UO 2 ) 2 (VO 4 ) 2 · 5H 2 O , In: Neues Jahrbuch für Mineralogie , Monatshefte, 1986, pp. 552-560
- ↑ Mindat - Number of localities for Fancevillit
- ↑ Find location list for Francevillite at the Mineralienatlas and at Mindat