Umohoit
| Umohoit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (UO 2 ) MoO 4 · 2H 2 O |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.GC.10 ( 8th edition : VI / G.05) 49.02.02.01 |
| Crystallographic Data | |
| Crystal system | triclinic |
| Crystal class ; symbol | triclinic pinacoidal; 1 |
| Space group | P 1 (No. 2) |
| Lattice parameters |
a = 6.375 Å ; b = 7.529 Å; c = 14.628 Å, α = 82.64 °; β = 85.95 °; γ = 89.91 ° |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 2 |
| Density (g / cm 3 ) | measured: 4.53-4.66; calculated: 4.523-4.457 |
| Cleavage | completely after {001} |
| colour | bluish black, olive green, black, orange |
| Line color | blue-gray |
| transparency | translucent to opaque, opaque |
| shine | Glass gloss |
| radioactivity | radioactive |
| Crystal optics | |
| Refractive indices |
n α = 1.66 n β = 1.831 n γ = 1.915 |
| Birefringence | δ = 0.255 |
| Optical character | biaxial negative |
| Axis angle | 2V = 65 ° (measured) |
| Pleochroism | X = dark blue, Y = light blue, Z = olive green |
Umohoit is a very rare occurring uranium - mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the triclinic crystal system with the chemical composition (UO 2 ) MoO 4 · 2H 2 O and develops mostly translucent or opaque crystals of bluish black, black, olive green or orange color. The crystal surfaces have a glass-like sheen .
Etymology and history
The name Umohoit is derived from its chemical composition and stands for the elements uranium (U), molybdenum (Mo), hydrogen (H) and oxygen (O). From a chemical point of view, the mineral is a hydrous uranyl molybdate . It was first investigated by GP Brophy and PF Kerr in 1953 using samples from Marysvale ; afterwards, several investigations into the crystal structure were made, with mostly the lattice parameters a and b being similar and c being clearly different in the samples. The cause was identified as the influence of humidity and temperature fluctuations during the measurements, so that Hamilton and Kerr stored the crystals in ethylene glycol during their measurements . As type locality is the Freedom No. 2 mine in Marysvale, Piute County , Utah in the United States .
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the umohoite belonged to the mineral class of " sulfates , chromates , molybdates and tungstates (as well as some selenates and tellurates)" and there to the department of "molybdates and wolframates", where he together with Moluranit and Mourit formed the unnamed group VI / G.05 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies umohoite in the “uranyl hydroxide” department. This is further subdivided according to the possible presence of additional cations and the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “With additional cations; with UO 2 (O, OH) 6 hexagonal polyhedra ”can be found, where it is the only member in the unnamed group 4.GC.10 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns umohoite to the class of "phosphates, arsenates and vanadates", but there also to the category of "molybdates and tungstates". Here he is to be found as the only member of the unnamed group 49.02.02 within the subdivision " Basic and water-containing molybdates and tungstates (hydrated) ".
Crystal structure
Umohoite crystallizes in the triclinic crystal system in the space group P 1 (space group no. 2) with the lattice parameters a = 6.375 Å , b = 7.529 Å, c = 14.628 Å and four formula units per unit cell .
In 2000, Krivovichev and Burns were able to elucidate the crystal structure of umohoite on a mineral sample from an unknown site on the territory of the former Soviet Union using an opaque, black single crystal. The crystal structure of umohoite consists of layers of uranyl molybdate that follow the uranophane anion topology. In these layers there are pentagonal-bipyramidal coordinated uranyl (VI) cations, the tips of which represent the uranyl oxygen atoms. In the equatorial plane there are five oxygen atoms, four of which are shared with the adjacent uranyl and molybdate units and one with two adjacent molybdate units. The molybdenum (VI) atoms are coordinated to form distorted octahedra , one octahedron tip being occupied by an oxide ion and the other by an oxygen atom of a water molecule. The layers are only held together by hydrogen bonds. Molecules of water of crystallization alternate between the layers. In their analysis, the authors do not rule out the possibility that small amounts of molybdenum (V) ions, which are responsible for its black color, are also present in the crystal under investigation. Due to the crystal structure, the empirical formula can therefore also be written as [(UO 2 ) MoO 4 (H 2 O)] (H 2 O) to represent the coordination of the water molecules to the Mo atoms.
properties
The mineral is very radioactive due to its uranium content of up to 53.13 % by weight . Taking into account the proportions of the radioactive elements in the idealized empirical formula and the Folgezerfälle of the natural decay chains a specific activity of about 95.109 k for the mineral Bq stated / g (compared to natural potassium 0.0312 kBq / g). However, the quoted value can vary significantly depending on the mineral content and composition of the levels; selective enrichment or depletion of the radioactive decay products are also possible and change the activity.
Education and Locations
Umohoite forms as a rare transformation product in the edge area and above the groundwater level of primary uranium ore deposits. Depending on where it was found , the mineral is associated with uraninite , ilsemannite , jordisite , iriginite , schoepite , uranophane , rutherfordin , calcurmolite , fluorite , pyrite , gypsum and quartz . Locations include:
- Shinkolobwe ( Kasolo Mine ) in the Democratic Republic of the Congo
- in Rabejac near Lodève and Mas d 'Alary , Hérault department, Languedoc-Roussillon region in France
- Kyzylsai Mo-U deposit in the Shu-Ili Mountains , Almaty Oblast , Kazakhstan
- and in the USA:
- at the Alyce Tolino Mine in Cameron, Coconino County , Arizona
- in Branch Ranch, Guadalupe County , New Mexico
- in the McLean Mine, Ray Point District, Live Oak County , Texas
- in the Marysvale District
- in the Prospector Mine
- in Freedom No. 1 Mine & Freedom No. 2 mine in Piute County
- in Freedom No. 2 Occurrence in the Gold Mountain District , Sevier County , Utah
- at the Lucky MC Mine (Lucky Mac), Gas Hills District , Fremont County , Wyoming
Precautions
Due to the high level of radioactivity and toxicity , mineral samples from Umohoit 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 face masks and gloves should be worn when handling the mineral .
See also
literature
- Robert G. Coleman & Daniel E. Appleman: Umohoite from the Lucky Mc Mine, Wyoming . In: American Mineralogist . Volume 42, 1957, pp. 657–660 ( PDF 228 kB )
- Peggy Kay-Hamilton & Paul F. Kerr: Umohoite from Cameron, Arizona . In: American Mineralogist . Volume 44, 1959, pp. 1248–1260 ( PDF 242 kB )
Web links
Individual evidence
- ↑ a b c Umohoit at Webmineral.com
- ↑ a b c d e Umohoit . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 69 kB )
- ↑ a b c Mindat - Umohoit at Mindat.org
- ↑ a b B. de Vivo: Uranium geochemistry, mineralogy, geology, exploration and resources: Published for the Institution of Mining and Metallurgy . Springer Science & Business Media, December 6, 2012, ISBN 978-94-009-6060-2 , p. 62.
- ^ A b SV Krivovichev and PC Burns: Crystal chemistry of uranyl molybdates. I. The structure and formula of umohoite In: The Canadian Mineralogist 2000, Volume 38, pp. 717-726. (English, PDF, 333 kB)
- ↑ PC Burns, ML Miller and RC Ewing: U6 + minerals and inorganic phases: a comparison and hierarchy of crystal structures In: The Canadian Mineralogist 1996, Volume 34, pp. 845–880. (English, PDF, 3.5 MB) ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
