Coffinite
| Coffinite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | U 4+ [(SiO 4 ), (OH) 4 ] |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.AD.30 ( 8th edition : VIII / A.09) 05.51.02.04 |
| Similar minerals | Zircon , Hafnon , Thorite , Huttonite , Uraninite |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetragonal-dipyramidal 4 / m 2 / m 2 / m |
| Room group (no.) | I 4 1 / amd (No. 141) |
| Lattice parameters | a = 6.99 Å ; c = 6.26 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | measured: 5.1 |
| Cleavage | irregular to slightly mussel-like |
| Break ; Tenacity | brittle |
| colour | black to brown |
| Line color | grey black |
| transparency | opaque, transparent in very thin layers |
| shine | Glass gloss |
| radioactivity | very radioactive |
| Crystal optics | |
| Refractive indices |
n α = 1.730 to 1.750 n β = 1.730 to 1.750 |
| Birefringence | δ = 1.730 |
| Optical character | uniaxial alternating |
The mineral coffinite is an island silicate from the zirconium group with the chemical composition U 4+ [(SiO 4 ), (OH) 4 ]. It crystallizes in the tetragonal crystal system and rarely develops small crystals larger than 20 μm. It is usually found in the form of colloidal and kidney crusts or radial, fibrous, massive or powdery mineral aggregates of black to brown color. Coffinite is abundant at individual sites, but overall not very widespread.
Etymology and history
Coffinit was first discovered in “La Sal No. 2 Mine “on Beaver Mesa in Mesa County , Colorado and described in 1956 by LR Stieff, TW Stern and AM Sherwood, who named the mineral after the American geologist Reuben Clare Coffin (1886–1972) in order to carry out his pioneering research into the Honor uranium deposits on the Colorado Plateau.
classification
Already in the now outdated, but still in use 8th edition of the mineral systematics according to Strunz , the coffinite belonged to the mineral class of "silicates and germanates" and there to the department of " island silicates (nesosilicates)", where it together with Hafnon , Reidit , Thorit , Thorogummit and Zirkon formed a separate 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 coffinite to the class of "silicates and germanates" and there in the department of "island silicates (nesosilicates)". However, this section is now further subdivided according to the presence of further anions and the coordination of the cations , so that the mineral can be found according to its composition in the subdivision of "Island silicates without further anions with cations in octahedral [6] and usually greater coordination", where it, also together with Hafnon, Thorit, Thorogummit and Zircon, forms the unnamed group 9.AD.30 .
The systematics of minerals according to Dana also assigns the coffinite to the class of "silicates and germanates" and there in the department of "island silicate minerals ". Here it is together with zircon, hafnon, thorite, thorogummite and steadindite in the " zircon group" with the system no. May 51, 2002 to be found in the subsection of " Island silicates: SiO4 groups only with cations in> [6] coordination ".
Crystal structure
Coffinite crystallizes tetragonally in the space group I 4 1 / amd (space group no. 141) with the lattice parameters a = 6.99 Å and c = 6.26 Å as well as 4 formula units per unit cell .
Structurally, coffinite belongs to the zirconium - titanite group . By substitution of considerable amounts of other elements may occur, in particular thorium instead of uranium . There is extensive miscibility between coffinite and thorite. Due to its own radioactivity, the crystal lattice is often destroyed and the mineral metamict .
Coffinite is one of the island silicates , i.e. the SiO 4 tetrahedra are not connected to one another.
properties
The mineral is classified as highly radioactive due to its uranium content of up to 72.6% and has a specific activity of 130.016 k Bq / g (for comparison: natural potassium 31.2 Bq / g).
Modifications and varieties
Uranothorite is a variety with high levels of thorium.
Education and Locations
Coffinite forms in hydrothermal veins and hydrothermally mineralized fault zones (e.g. Dolní Rožínka , Czech Republic ). It is also found in sedimentary uranium deposits in sandstones (e.g. Colorado). Accompanying minerals include uraninite , thorite , pyrite , marcasite , roscoelite as well as various clay minerals and amorphous organic substances.
So far (as of 2011), coffinite has been found at around 500 sites worldwide. In addition to its type locality , the mineral was found in many other places in the United States in the states of Arizona , Colorado , New Mexico , Texas , Utah and Wyoming as well as at Koyuk and Ketchikan in Alaska, on the Kern River and Sonora Pass in California, near East Granby ( Hartford County ) in Connecticut, in the Stanley Basin ( Custer County in Idaho), the uranium deposit in Dawes County in Nebraska, in Humboldt County and on the Reese River ( Lander County ) in Nevada, near Bedford ( Westchester County ) in New York Lakeview ( Lake County ) and McDermitt District ( Malheur County ) in Oregon, Jim Thorpe in Pennsylvania, Fall River County in South Dakota, Pittsylvania County in Virginia, Stevens County and Castle Peak ( Whatcom County ) in Washington.
Well-known sites are above all the deposits on the Colorado Plateau (Woodrow Mine, New Mexico), where the mineral acts as the main carrier of uranium in addition to pitchblende . The same applies to the “Ogame Mine” in Japan.
In Germany, coffinite is found together with pitchblende mainly in the Black Forest in Baden-Württemberg; in Franconia , near Miltach and the Upper Palatinate in Bavaria; in the Hessian Odenwald ; at several sites in Rhineland-Palatinate ; near Mansfeld in Saxony-Anhalt; in the Ore Mountains and Vogtland in Saxony and near Ronneburg in Thuringia.
In Austria, coffinite was found on the Hüttenberger Erzberg in Carinthia, on the forest tunnel on the A9 near Wald am Schoberpaß in Styria and on the Graschberg near Thierbach (Wildschönau municipality) in Tyrol.
In Switzerland, the mineral was found at Kaisten AG and Riniken in the canton of Aargau, Lavey-les-Bains in the canton of Vaud and at Collonges VS and Les Marécottes in the canton of Valais.
Other locations are in Egypt , Argentina , Australia , Bolivia , Brazil , Bulgaria , Canada , China , Czech Republic , Finland , France , Gabon , Greenland , Guyana , India , Kazakhstan , Mongolia , New Zealand , Niger , Nigeria , Norway , Poland , Portugal , Russia , Zambia , Sweden , Slovakia , Slovenia , Spain , South Africa , Hungary , Uzbekistan , the United Kingdom (Great Britain) and the United States of America (USA).
use
Coffinite is an economically important mineral for the extraction of uranium.
Precautions
Due to the toxicity and the strong radioactivity of the mineral, mineral samples from Coffinit should only be kept in dust- 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 .
Individual evidence
- ↑ 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. 543 .
- ↑ a b Webmineral - Coffinit (engl.)
- ↑ a b Handbook of Mineralogy - Coffinite (English, PDF 75 kB)
- ↑ a b Coffinit at mindat.org (engl.)
- ↑ Mindat - Localities for Coffinite
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 671 .
- HJ Rößler: Textbook of Mineralogy . VEB German publishing house for basic industry, Leipzig 1981
See also
Web links
- Mineral Atlas: Coffinite (Wiki)