Françoisite- (Ce)
| Françoisite- (Ce) | |
|---|---|
_(80x,_Bildbreite_2,9_mm)_-_La_Creusaz.jpg) |
|
| General and classification | |
| other names |
IMA 2004-029 |
| chemical formula | (Ce 0.6 Nd 0.3 Ca 0.1 ) [(UO 2 ) 3 | (O) (OH) | (PO 4 ) 2 ] • 6H 2 O |
|
Mineral class (and possibly department) |
Phosphates, arsenates, vanadates |
|
System no. to Strunz and to Dana |
8.EC.05 ( 8th edition : VII / E.07) April 42, 2014 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | 2 1 / b |
| Lattice parameters | a = 9.295 Å ; b = 15.53 Å; c = 13.71 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | 4.62 |
| Cleavage | after {010} |
| Break ; Tenacity | uneven |
| colour | lemon yellow |
| Line color | Please complete |
| transparency | Please complete |
| shine | Please complete |
| radioactivity | highly radioactive |
Françoisit- (Ce) is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the composition (Ce 0.6 Nd 0.3 Ca 0.1 ) [(UO 2 ) 3 | (O) (OH) | (PO 4 ) 2 ] · 6H 2 O, so it is chemical seen a cerium - containing uranyl phosphate .
Françoisit- (Ce) only develops very small, 0.1 mm long, needle-like lemon-yellow crystals and is known from only two sites so far.
Special properties
The mineral is very radioactive due to its uranium content of up to 56.1 % by weight . Taking into account the natural decay series, a specific activity of about 100.1 k Bq / g is given for Françoisite- (Ce) (for comparison: natural potassium 0.0312 kBq / g).
Etymology and history
The mineral was named after its Nd analogue Françoisit- (Nd) , which was discovered in 1988. This was named in honor of the Belgian geologist Armand François (* 1922), who was the chief geologist of the national Congolese mining company Gécamine.
classification
Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Françoisit- (Ce) belonged to the mineral class of "phosphates, arsenates, vanadates" and there to the department of "uranyl phosphates and uranyl vanadates", where together with Althupit , Arsenuranylit , Bergenit , Dewindtit , Dumontit , Françoisit- (Nd) , Hügelit , Kamitugait , Kivuit , Metavanmeersscheit , mundite , Phosphuranylit , Phuralumit , Phurcalit , Vanmeersscheit and Yingjiangit the unnamed group VII / E.07 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), also assigns the Françoisite- (Ce) to the class of "phosphates, arsenates and vanadates" and there in the department of "uranyl phosphates and Arsenate ”. However, this section is further subdivided according to the molar ratio of uranium oxide complex (UO 2 ) and phosphate or arsenate complex (RO 4 ), so that the mineral can be found in the sub-section "UO 2 : RO 4 = 3: 2" according to its composition , where together with Françoisit- (Nd), Phuralumit and Upalit the "Upalit-Phuralumit-Gruppe" with the system no. 8.EC.05 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the francoisite (Ce) to the class of "phosphates, arsenates, vanadates", but there in the category of "water-containing phosphates etc., with hydroxyl or halogen". Here, together with francoisite (Nd), it forms the francoisite group within the subdivision of “ water-containing phosphates etc., with hydroxyl or halogen with (AB) 5 (XO 4 ) 2 Z q × x (H 2 O) ”.
Education and Locations
Françoisite- (Ce) is found in weathered hydrothermal breccias in which it forms sea urchin-like bright yellow aggregates. It is often associated with nováčekite / metanováčekite, jarosite and, more rarely, metatorbernite , metazeunerite , arsenuranospathite , uranospathite and hyalite . The primary rock-forming mineral is often monazite (Ce) . Françoisite- (Ce) from Arkaroola is formed due to the presence of regional hydrothermal systems that are rich in hematite , copper , uranium , niobium and the rare earth elements . The mineral eventually crystallizes in cavities created after uranium ore minerals dissolve. The direct accompanying minerals are barite , metatorbernite and clay minerals of the kaolinite group.
So far, the mineral is only known from its two type localities. The first site is the La Creusaz uranium mine near Les Marécottes in the Vallé du Trient in the canton of Valais in Switzerland , the second site is mine No. 2, Radium Ridge near Arkaroola in Australia . From Bangobé in Gabon , a cerium-rich francoisite (Nd) is known which contains almost equal proportions of Ce and Nd.
Crystal structure
Françoisit- (Ce) crystallizes monoclinically in the space group 2 1 / b with the lattice parameters a = 9.295 Å ; b = 15.53 Å and c = 13.71 Å as well as four formula units per unit cell .
See also
literature
- Nicolas Meisser, Joël Brugger, Stefan Ansermet, Philippe Thélin, François Bussy: Françoisite- (Ce), a new mineral species from La Creusaz uranium deposit (Valais, Switzerland) and from Radium Ridge (Flinders Ranges, South Australia): Description and genesis . In: American Mineralogist . tape 95 , no. 10 , January 10, 2010, p. 1527–1532 , doi : 10.2138 / am.2010.3413 .
