Davidite
| Davidite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (Ce, La, Y, U) 2 Fe 2 3+ (Ti, Fe 3+ ) 18 O 38 |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.CC.40 ( 8th edition : IV / C.09) 08.05.01.05 (-La), 08.05.01.06 (-Ce) and 08.05.01.11 (-Y) |
| Crystallographic Data | |
| Crystal system | trigonal |
| Crystal class ; symbol | trigonal-rhombohedral; 3 |
| Space group | R 3 (No. 148) |
| Lattice parameters | see crystal structure |
| Formula units | Z = 3 |
| Physical Properties | |
| Mohs hardness | 6th |
| Density (g / cm 3 ) | 4.29 to 4.48 |
| Cleavage | is missing |
| Break ; Tenacity | uneven to slightly scalloped; brittle |
| colour | black to gray-black |
| Line color | black |
| transparency | opaque |
| shine | Glass gloss |
| radioactivity | weak to strong |
Davidite is the collective name for an unspecified mineral of the series davidite (Ce) , davidite (La) and davidite (Y) (formerly gramaccioliite (Y) ) from the mineral class of " oxides and hydroxides ". All three minerals crystallize in the trigonal crystal system with the general chemical composition (Ce, La, Y, U) 2 Fe 2 3+ (Ti, Fe 3+ ) 18 O 38 The elements given in the round brackets can be mutually exclusive in the formula represented ( substitution , diadochie), but are always in the same proportion to the other components of the mineral.
Davidite is opaque and mostly develops well-developed, albeit crude crystal forms up to about 30 cm in size with a cubic or pyramidal habit , but can also be found in the form of granular to massive mineral aggregates, predominantly black to dark gray in color. Reddish and brownish colors are produced by partially weathered and / or oxidized surfaces.
Etymology and history
Davidite was first discovered in the "Radium Hill Mine" on Radium Hill in South Australia. It was first described, but still as a single mineral, in 1906 by Douglas Mawson (1882-1958), who named it after the Australian geologist Tannatt William Edgeworth David (1858-1934).
However, later analyzes showed that davidite is a mixed series with a total of three end links. The mineral with the predominant lanthanum content was therefore renamed Davidit- (La). Davidite- (Ce) was described by Levinson in 1966 and Davidit- (Y) in 2002 by Pasero, Olmi and Orlandi.
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Davidites belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with the molar ratio of metal: oxygen = 2: 3", where he and Cleusonite , Crichtonit , Dessauit- (Y) , Landauit , Lindsleyit , Loveringit , Mathiasit and Senait formed the unnamed group IV / C.09 .
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 Davidite to the class of "oxides and hydroxides" and there into the department of "oxides with the molar ratio of metal: oxygen = 2: 3, 3: 5 and comparable “. However, this section is further subdivided according to the size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With large and medium-sized cations”, where it is found together with Cleusonite, Crichtonite, Dessauit- (Y), Gramaccioliite- (Y), Landauit, Lindsleyit, Loveringit, Mathiasit and Senait forming the unnamed group 4.CC.40 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Davidite to the class of "oxides and hydroxides" and there in the division of "multiple oxides with Nb, Ta and Ti". Here he is together with Cleusonit, Crichtonit, Dessauit, Landauit, Lindsleyit, Loveringit, Mathiasit and Senait in the "Crichtonitgruppe (ABC 18 T 2 O 38 )" with the system no. May 8, 2001 to be found in the subsection of " Multiple Oxides with Nb, Ta and Ti ".
Crystal structure
All davidites crystallize trigonal in the space group R 3 (space group no.148) with 3 formula units per unit cell , but with slightly different lattice parameters :
- Davidite- (Ce): a = 10.28 Å and c = 20.81 Å
- Davidite- (La): a = 10.38 Å and c = 20.91 Å
- Davidite- (Y): a = 10.41 Å and c = 20.97 Å
properties
Davidite (Ce) and davidite (La) are classified as highly radioactive due to their uranium content of up to 3% and radioactive isotopes of the rare earths cerium and lanthanum and have a specific activity of about 5.8 k Bq / g (for comparison: natural potassium 0.031.2 kBq / g). Davidite- (Y), on the other hand, is only classified as slightly radioactive due to its lower uranium content and a specific activity of 488 Bq / g.
Due to their own radioactivity , davidites are mostly completely metamictic , i.e. the internal structure has been lost over time and the material is amorphous despite the retained external crystal shape . This condition is also the reason for its black color and opacity. However, it can be recrystallized by heating to around 1000 ° C.
Education and Locations
Davidite- (La) as the most common form of the minerals forms primarily in high-grade hydrothermal veins with high contents of rare earths, including norites and anorthosites . It can also be found in alkaline rocks, granitic pegmatites and carbonatites . The same formation conditions apply to davidite (Ce) and davidite (Y) as closely related minerals. Davidite is associated with albite , allanite , apatite , calcite , epidote , euxenite , gadolinite , ilmenite , magnetite , rutile , titanite , thortveitite , tourmaline , xenotime and zircon .
Precautions
Due to the toxicity and the strong radioactivity of the mineral, mineral samples should only be kept in dust- and radiation-tight containers, but especially never in living rooms, bedrooms or work rooms. Absorption into the body ( incorporation ) should also be prevented in any case and direct body contact should be avoided to be on the safe side and face masks and gloves should be worn when handling the mineral.
See also
literature
- John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Davidite- (Ce) ( PDF 67.7 kB ) and Davidite- (La) ( PDF 109.4 kB ), in: Handbook of Mineralogy, Mineralogical Society of America , 2001
- Paul F. Kerr, HD Holland: DIFFERENTIAL THERMAL ANALYSES OF DAVIDITE , Columbia University, New York ( PDF 546.9 kB )
Web links
- Mineral Atlas: Davidite (Wiki)
- Mindat - Davidite- (Ce) and Davidite- (La) and Davidite- (Y)
- Webmineral - Davidite- (Ce) , Davidite- (La) and Gramaccioliite- (Y) (= Davidite- (Y))
Individual evidence
- ↑ a b c Stefan Weiss: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
- ↑ a b Webmineral - Davidite- (Ce) , Davidite- (La) and Gramaccioliite- (Y) (= Davidite- (Y))
- ↑ a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 201 .
- ↑ a b c Webmineral - Gramaccioliite- (Y) (= Davidite- (Y))
- ↑ Biography of Sir Douglas Mawson (1882–1958) ( Memento from August 15, 2014 in the Internet Archive ) (PDF; 680 kB)
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 518 (first edition: 1891).
- ↑ John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Davidit- (La) , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 (see literature)