Schoepit
| Schoepit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | [(UO 2 ) 4 | O | (OH) 6 ] • 6H 2 O |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.GA.05 ( 8th edition : IV / H.01) 02/05/01/03 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-pyramidal; mm 2 |
| Room group (no.) | P 2 1 ca (No. 29) |
| Lattice parameters | a = 14.34 Å ; b = 16.81 Å; c = 14.73 Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | ≈ 2.5 |
| Density (g / cm 3 ) | measured: 4.8 to 4.96; calculated: 4.87 |
| Cleavage | completely after {001} |
| Break ; Tenacity | brittle |
| colour | lemon yellow, sulfur yellow, brownish yellow |
| Line color | light yellow |
| transparency | transparent |
| shine | Diamond luster |
| radioactivity | very strong |
| Crystal optics | |
| Refractive indices |
n α = 1.690 n β = 1.714 n γ = 1.735 |
| Birefringence | δ = 0.045 |
| Optical character | biaxial negative |
| Axis angle | 2V = measured: 89 ° |
| Pleochroism | visible: X = c = colorless Y = b = lemon yellow Z = a = lemon yellow |
| Other properties | |
| Special features | green fluorescence |
Schoepit is a rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition [(UO 2 ) 4 | O | (OH) 6 ] · 6H 2 O and develops mostly transparent and diamond- shining crystals with tabular, but also short-prismatic habit according to {001} and lemon-yellow, sulfur-yellow or brownish yellow color with light yellow streak color . Microcrystalline mineral aggregates are also rare .
Etymology and history
Schoepit was first discovered in 1922 in the " Shinkolobwe Mine" (Kasolo Mine) in the province of Katanga, now part of the Democratic Republic of the Congo ( Zaire ), and described in 1923 by Thomas Leonard Walker , who named it after the Belgian geographer and mineralogist Alfred Schoep .
The type mineral is located in the Royal Ontario Museum in Toronto , Canada .
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Schoepit belonged to the mineral class of "oxides and hydroxides" and there to the department of "uranyl hydroxides and hydrates", where together with ianthinite , metaschoepite , metastudtite , Paraschoepit and Studtit formed an independent 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 Schoepit to the class of "oxides and hydroxides" and there in the department of "uranyl hydroxides". However, this section is further subdivided according to the possible presence of further cations , so that the mineral can be found according to its composition in the sub-section “Without additional cations”, where it only forms the schoepite group 4.GA.05 together with metaschoepite and paraschoepite .
The systematics of minerals according to Dana also assigns the Schoepit to the class of "oxides and hydroxides", but there in the department of "uranium and thorium-containing oxides". Here it can also be found together with Metaschoepit and Paraschoepit in the unnamed group 05.02.01 within the subdivision " Oxides containing uranium and thorium with a cation charge of 6+ (AO 3 ), and containing water ".
Crystal structure
Schoepit crystallizes orthorhombically in space group P2 1 ca (space group no. 29) with the lattice parameters a = 14.34 Å ; b = 16.81 Å and c = 14.73 Å and 8 formula units per unit cell .
The crystal structure of Schoepit is topologically identical to that of Fourmarierite . The uranium atom has a pentagonal-bipyramidal geometry, with the uranyl oxygen atoms sitting on the axes and the equatorial plane forming layers of edge and corner-linked oxygen atoms.
properties
The mineral is classified as very radioactive due to its uranium content of up to 72.9% and has a specific activity of around 130.5 k Bq / g (for comparison: natural potassium 0.0312 Bq / g).
Some schoepites show green fluorescence under UV light .
Modifications and varieties
In their investigation of various uranyl oxide hydrates, Christ and Clark noticed that the diffraction pattern of schoepite crystals shows the presence of three different phases. In their study, the authors come to the conclusion that these phases are Schoepit (" Schoepit I "), Metaschoepit (" Schoepit II ") and Paraschoepit (" Schoepit III "). You specify the following crystal parameters:
Schoepit I crystallizes orthorhombically in the space group Pbca (space group no. 61) with the lattice parameters a = 14.33 Å; b = 16.79 Å and c = 14.73 Å.
Schoepit II crystallizes orthorhombically in the space group Pbna (space group no. 60) with the lattice parameters a = 13.99 Å; b = 16.72 Å and c = 14.73 Å.
Schoepit III crystallizes orthorhombically in the space group Pbca (space group no. 61) with the lattice parameters a = 14.12 Å; b = 16.83 Å and c = 15.22 Å.
Some of the crystals examined showed an amber-brown core ( Schoepit I ), which was surrounded by yellow needle-shaped crystals ( Schoepit II or Schoepit III ), the morphology of which corresponds to that of the original crystal. The diffraction pattern of Schoepit III agrees with that which Schoep and Stradiot found for Paraschoepit as early as 1947. Even optically very pure amber-brown crystals ( Schoepit I ) show the presence of Schoepit II in the X-ray experiment . The dates for Schoepit I agree with those that Billiet and de Jing determined for Schoepit in 1935. The conversion of Schoepit I to Schoepit II and Schoepit III is attributed to the progressive loss of crystal water . Repeated examinations on these crystals showed that the conversion progresses continuously from phase I to phase II and / or phase III, even in an atmosphere saturated with water vapor. Completely yellow crystals of Schoepit III do not transform into Schoepit I again . It was also observed that if an amber-brown Schoepit crystal is split under the microscope with a needle, the split surfaces turn yellow due to the escaping crystal water. This dehydration could also be demonstrated by placing an amber-brown crystal over concentrated sulfuric acid . A yellow powder formed after a few hours.
Education and Locations
Schoepit forms as a rare alteration product of uraninite by hydrothermal processes in uranium - deposits and is correspondingly mostly in paragenesis with this, but also with Arsenuranylit , Becquerelit , Billietit , Curit , Fourmarierit , Ianthinit , Metazeunerit , Nováčekit , Paraschoepit , rutherfordine , Soddyit , Uranophan , Uranospinit and Vanden Dries log to find.
Schoepit is often found as a direct conversion product of Ianthinite, which is unstable in air. Complete pseudomorphoses according to Ianthinit are also called "Epi-Ianthinit". Schoepit itself slowly transforms into metaschoepit ((UO 3 ) · nH 2 O n≈2) in air, as the water of crystallization between the layers of the crystal lattice escapes first, so that it finally collapses and then rearranges it into a more stable one Structure comes. Usually the crystals of the Schoepit show adhesions of the two minerals. In this context, it is discussed that metaschoepit transforms itself further to “dehydrated schoepit” (((UO 3 ) · nH 2 O n≈ 0.75 - 1)).
As a rare mineral formation, Schoepit could only be proven at a few sites, whereby so far (as of 2013) around 90 sites are known. In addition to its type locality "Shinkolobwe Mine", the mineral was also found in the Democratic Republic of the Congo in the "Musonoi Mine" near Kolwezi and in the uranium mine east of Kamoto .
In Germany, Schoepit was found in the "Kirchheimerstollen" near Baden-Baden -Müllenbach, on the now inaccessible piles of the Krunkelbachtal uranium deposit near Menzenschwand and in the Clara mine near Oberwolfach in Baden-Württemberg; in the "Johannessschacht" near Wölsendorf in Bavaria; at the Bühlskopf near Ellweiler in Rhineland-Palatinate and near Schneeberg in the Saxon Ore Mountains.
The only previously known site in Switzerland is a rift on the Albigna glacier in the canton of Graubünden.
Other localities include Argentina, Australia, China, France, Gabon, Italy, Japan, Canada, Mexico, New Zealand, Norway, Russia, Tajikistan, the Czech Republic, Hungary, the United Kingdom (England, Scotland) and several federal states of the United States (Arizona, Colorado, Maine, New Hampshire, Utah).
See also
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 559 .
- Schoepite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 71.8 kB )
Web links
- Mineral Atlas: Schoepit (Wiki)
- Photos of Schoepit on the website of the Association des Géologues Amateurs de Belgique (AGAB)
Individual evidence
- ↑ a b Webmineral - Schoepite (English)
- ↑ a b c d 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. 249 .
- ↑ a b Handbook of Mineralogy - Schoepite ( English, 71.8 kB; PDF )
- ↑ a b c d Mindat - Schoepite (English)
- ↑ TL Walker, "Schoepite, a new uranium mineral from Kasolo, Belgian Congo", In: "American Mineralogist" 1923, 8, pp. 67-69 ( PDF 164 kB )
- ↑ RJ Finch, MA Cooper, FC Hawthorne, RC Ewing, "The crystal structure of schoepite, [(UO 2 ) 8 O 2 (OH) 12 ] (H 2 O) 12 ", In: "The Canadian Mineralogist" 1996, 34, pp. 1071-1088 ( PDF 1.4 MB )
- ^ CL Christ, Joan R. Clark: Crystal Chemical Studies Of Some Uranyl Oxide Minerals . In: The American Mineralogist. 1960, 45, 1026-1061 PDF (English) 2.1 MB
- ↑ PC Burns, RJ Finch, FC Hawthorne, ML Miller, RC Ewing, "The crystal structure of ianthinite, [U 4+ 2 (UO 2 ) 4 O 6 (OH) 4 ] (H 2 O) 5 " In: " Journal of Nuclear Materials "1997, 249, pp. 199-206
- ↑ RJ Finch, FC Hawthorne, RC Ewing "Structural relations among schoepite, metaschoepite, and" dehydrated schoepite "", In: "The Canadian Mineralogist" 1998, 36, pp. 831–845 ( PDF 1.9 MB )
- ↑ Mindat - Number of localities for Schoepit
- ↑ Find location list for Schoepit at the Mineralienatlas and at Mindat