Uraninite

• Pitchblende
• Pitchblende
• Uranit
• Uranin

Uraninite ( among other things, also known as pitchblende or Bechblende ) is a commonly occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the cubic crystal system with the composition UO2, is so chemically seen a uranium (IV ) oxide. By the radioactive decay series of uranium uraninite always contains a certain amount of lead oxide (PbO ) that can be up to 20 % depending on the geological age.

Uraninite usually develops cubic or octahedral crystals or combinations thereof, but also low one, granular or massive aggregates in gray, black and brownish in color with brownish-black to greenish stroke color. In general, uraninite is opaque, only fine splinters and thinnest layers are reddish brown translucent. Fresh samples have a pitch - to -fat -like, occasionally weak metallic luster, which, however, after some time due to weathering is matt.

Special Features

Due to its uranium content of up to 88.15 % uraninite is one of the strongest natural sources of radiation. The uranium is in secular equilibrium with its daughter nuclides, has pure uraninite a specific activity of about 157.8 kBq / g (compared to natural potassium 0.0312 kBq / g; spent nuclear fuel 18,000,000 kBq / g). Therefore uraninite should be stored and processed in accordance with strict safety precautions.

Uraninite is usually at least partially metamict ( isotropisiert ), that is, its crystal lattice was destroyed by its own radioactivity partly to mostly, but are in contrast to other, uranium poorer minerals mostly remnants of the crystal lattice detectable. Nevertheless, go certain physical properties such as the cleavage is lost and the outside still crystalline acting samples show a conchoidal fracture.

Also interesting is the high variability of the density which is initially about 10.63 to 10.95 g / cm ³, but slowly decreases with increasing geological age to about 9 to 7.5 g / cm ³. Derbe and kollomorphe varieties can especially in weathering are relatively easy and even very clearly fall below 7. Uraninite is often accompanied weathering products of brightly colored (red, yellow, rarely green).

The mineral may rarely form with columbite epitaxies. Uraninite crystals grow in certain directions aligned with Columbitkristallen. It forms the first end member of the perfect mix series (mixed crystal) uraninite - thorianite. Thorium -containing uranium Destinite are called inter alia Bröggerit. Younger uranium Destinite shine glass to pechartig, while the older copies more and more metallic shine. Weathering influences and metamorphosis let the metal shine disappear.

Etymology and history

One of the oldest mentions of the mineral was made in 1565 by John Kent man who called it Plumbago sterilis pici similis Bechblende ( pitchy sterile panel). This he had acquired by the Saxon miners, who promoted the mineral from the silver - cobalt transitions of the Ore Mountains. They had no use for the pitch-black stones and rejected the supposedly metal-free diaphragm.

Later to find different colors on the old dumps oxidation products on the discarded pitchblende were, they were cut to obtain this new beautiful colors. As already oxidized materials were consumed, the colors were also produced in a certain scale from pitchblende. Therefore today are radioactively contaminated some old works of art. Since it was recognized that the pitchblende consists of a compound of various uranium oxides that are deposited as kollomorphes aggregate, the term is used only for this batch.

Martin Heinrich Klaproth (1743-1817) 1789 was isolated from pitchblende the element uranium, which he initially described as Uranit 1790 but renamed the rules of analogy, according to uranium. The term Uranit was subsequently used as a synonym for various uranium minerals. From Klaproth also comes the misnomer sulfurized Uranit. Later he took over the embossed name of Karsten 1792 Uranerz. Other synonyms are pęcherz (of Werner), pitchblende ( Leonhard ), pitch uranium ( Hausmann ) and Nasturan ( rough KOBELL of 1853 from the Greek ναστός for tight or ). Haidinger finally introduced the term uranine as a designation for the mineral, which was transferred from Dana in the still valid naming uraninite.

Although the mineral was formerly known as described, taken as the type locality for the transition uraninite deposit Jachymov (now Jáchymov ), from where it FE Brückmann has described 1727. The pitchblende, which took Klaproth to the discovery of uranium comes from the pit Georg Johann George Wagsford in town in the Saxon Erzgebirge. In contrast, uranium compounds used by the French physicist Antoine Henri Becquerel not, as is often asserted, pitchblende to the discovery of radioactivity in 1896, but man-made. The Polish-French chemist and Nobel Prize winner Marie Curie used for their research that led to the discovery of polonium and radium uranium decay products, initially pitchblende. For cost reasons, but they used mainly the processing waste ( tailings ) of uranium color production from Jáchymov in which these rare elements were already enriched compared to Ursprungserz. A ton contains about 0.1 g of radium.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the uraninite belonged to the mineral class of " oxides and hydroxides " and then to the Department of " oxides with the molar ratio of metal: oxygen = 1: 2 ," where he along with baddeleyite, Calzirtit, cerianite - (Ce), Hiärneit, Tazheranit and thorianite formed a distinct group.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz 's Mineral classification assigns the uraninite also in the class of " oxides and hydroxides " and there in the department of " Metal: Oxygen = 1: 2 and comparable " one. This division, however, is further divided according to the size of the involved cations and the crystal structure, so that the mineral according to its composition and structure in the subdivision " with large (± medium-sized ) cations; Fluorittypische structures "can be found, where it forms the unnamed group 4.DL.05 together with cerianite - (Ce), and thorianite zirkelite.

The mainly common in English-speaking classification of minerals according to Dana assigns the uraninite in the class of " oxides and hydroxides ", There, however, in the department of " uranium and thorium- containing oxides ." Here it is only to be found along with thorianite in the unnamed group 05:01:01 within the sub-division of " uranium and thorium oxides with a cation charge of 4 ( AO2 ) ".

Modifications and varieties

Pitchblende consists essentially of U3O8, U3O7 rarely, plus other metal oxides with lead, iron, thorium and rare earth metals and received the designation because of the often black color and greasy luster, which looks very similar to the tar-like substance out of luck.

Nierig - spherical varieties are called Blasenerz. Oily shiny rough variants called pęcherz. When individual spheres " peep " through the matrix they are called because of their black color like mouse eyes. Thorium -containing pieces pegmatisch formed are called Bröggerit. The so-called high-grade ore referred only pieces that rather call this much of a mineral. The name is not just limited to uraninite.

Education and Locations

In the following deposits occurs uraninite / pitchblende:

• Hydrothermal vein ( Saxon- Bohemian Erzgebirge, Pribram, Czech Republic; Krunkelbachtal at Menzenschwand, Black Forest; Massif Central France)
• Unconformity deposits ( Athabasca Basin, Canada, Northern Territory, Australia)
• Sediment- bound deposits in sandstones, carbonates, coal ( Königstein, Saxony; Culmitzsch, Thuringia; Freital, Saxony, Curnamona Province, South Australia, Colorado Plateau, USA; Niger)
• Black slate- bound deposits ( Ronneburg, Thuringia )
• Iron -Oxide- Copper - Gold deposits ( Olympic Dam, South Australia)
• To volcanic bound ( Streltsovka Caldera at Krasnokamensk, Russia; Delitzsch, Saxony )
• Pegmatites (Norway )

Crystal structure

Uraninite crystallized in the cubic crystal system in the space group Fm3m with lattice parameters a = 5.47 Å and four formula units per unit cell. Its crystal structure is isotypic with fluorite ( CaF2). The U4 cations thereby form a cubic close packing, with the tetrahedral sites are fully occupied by oxide anions, that is, each oxygen atom is surrounded by four uranium atoms tetrahedrally. The uranium (IV ) cations in turn thus have a coordination number of CN = ​​8, as coordination polyhedra results here a cube.

Use

Uraninite is the most economically important uranium mineral. In the 19th and early 20th century uraninite for the production of paints, and for the extraction of radium (eg Jáchymov ( Joachimsthal ), Czech Republic ) was obtained. In the period of the Cold War was far above the energy out continuous demand for uranium for the production of nuclear weapons and for the production of plutonium in nuclear reactors. In the Erzgebirge there rich uranium deposits were mined by the Soviet- German Aktiengesellschaft ( SDAG ) bismuth in the GDR on a large scale and placed in pre-processed form ( Seelingstädt, Crossen ) in the Soviet Union. From the 1970s, the production of uranium dominated for energy.

With the political changes in 1989, there was a sharp drop in uranium production. At this time already played the uranium production for nuclear weapons between the two superpowers no longer any major, but both sides had amassed large strategic reserves, which were released and the world price expressed strong. Also, now new producers came with lowest prices in Central Asia on the open market.

Precautions

Due to the toxicity and the high radioactivity of the mineral mineral samples should be stored in a dust - and radiation- proof containers, especially but never in living, sleeping and working areas. Similarly, inclusion in the body ( incorporation or ingestion) should be definitely prevented and the safety of direct body contact and worn when handling the mineral mask and gloves.