Carnotite

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Carnotite
Carnotite-96138.jpg
Group of carnotite crystals from the "Mashamba West Mine" near Kolwezi , Democratic Republic of the Congo
General and classification
chemical formula K 2 [UO 2 | VO 4 ] 2  • 3H 2 O
Mineral class
(and possibly department) 		Oxides and hydroxides (formerly phosphates, arsenates and vanadates)
System no. to Strunz
and to Dana 		4.HB.05 ( 8th edition : VII / E.11)
40.02a.28.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Room group (no.) P 2 1 / a (No. 14)
Lattice parameters a  = 10.47  Å ; b  = 8.41 Å; c  = 6.59 Å
β  = 103.8 °
Formula units Z  = 2
Physical Properties
Mohs hardness 2
Density (g / cm 3 ) 3.7 to 4.7
Cleavage completely after {001}
Break ; Tenacity uneven, brittle
colour light to dark yellow, yellow-green
Line color light yellow
transparency translucent
shine Silk gloss, earthy matt
radioactivity very radioactive
Crystal optics
Refractive indices n α  = 1.750
n β  = 1.925
n γ  = 1.950
Birefringence δ = 0.200
Optical character biaxial negative
Axis angle 2V = measured: 43 ° to 60 °; calculated: 26 ° to 36 °

Carnotite is a frequently occurring mineral from the mineral class of " oxides and hydroxides " (formerly phosphates, arsenates and vanadates). It crystallizes in the monoclinic crystal system with the chemical composition K 2 [UO 2 | VO 4 ] 2  • 3H 2 O and develops mostly massive or earthy mineral aggregates , but rarely tabular to needle-like crystals up to about 2 mm in size from light to dark green or yellow-green color with light yellow streak color .

Etymology and history

Carnotite was first discovered in the "Rajah Mine" near Uravan in Montrose County (Colorado) in the USA and described in 1899 by Charles Friedel and Edouard Cumenge , who named the mineral after the French chemist Marie Adolphe Carnot .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , carnotite belonged to the mineral class of " phosphates , arsenates and vanadates " and there to the department of "uranyl phosphates and uranyl vanadates ", where it belonged to Curienit , Francevillit , Margaritasite , Metatyuyamunit , Metavanuralit , Sengierit , Strelkinit , Tyuyamunit and Vanuranylit 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), assigns carnotite to the class of "oxides and hydroxides" and there in the division of "V [5,6] vanadates" . This section is further subdivided according to the crystal structure, so that the mineral can be found in the sub-section "Uranyl group vanadates (Sorovanadate)", where it only forms the unnamed group 4.HB.05 together with margaritasite .

The systematics of minerals according to Dana , which is predominantly used in the English-speaking world , assigns carnotite to the class of "phosphates, arsenates and vanadates" like the outdated Strunz'sche systematics, but there it belongs to the category of "water-containing phosphates etc.". Here it is together with margaritasite in the unnamed group 40.02a.28 within the subdivision of “ Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O), with (UO 2 ) 2+ ”.

Crystal structure

Carnotite crystallizes monoclinically in the space group (space group no. 14) with the lattice parameters a  = 10.47  Å ; b  = 8.41 Å; c  = 6.59 Å and β = 103.8 ° and 2 formula units per unit cell .

properties

The mineral is classified as very radioactive due to its uranium content of up to 52.8% and has a specific activity of around 94.46 k Bq / g (for comparison: natural potassium 31.2 Bq / g).

Carnotite is often difficult to distinguish from other uranium minerals; X-ray structure analyzes are occasionally necessary for this.

Education and Locations

Carnotite is formed as sedimentary rock by deposits in vanadium and uranium-rich waters . Accompanying minerals include tyuyamunite , metatyuyamunite , volborthite , tangite , metatorbernite , rossite , hewettite and other uranium or vanadium oxides as well as gypsum and barite .

So far (as of 2011), carnotite has been found at around 1100 sites worldwide. Important deposits are located in the US state of Colorado , in Namibia ( Langer Heinrich Mine) and in Morocco . Other locations include the Democratic Republic of the Congo , Colorado and Utah in the USA , and Tyuya Muyun in Uzbekistan .

use

The high uranium dioxide content of 63 percent, which is responsible for the radioactivity of the mineral, makes it an important uranium and vanadium ore.

Precautions

Due to the toxicity and the strong radioactivity of the mineral, mineral samples of carnotite should only be kept in dust- and radiation-proof containers, but especially never in living rooms, bedrooms or work rooms. 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 .

See also

Individual evidence

  1. ↑ 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 .
  2. ↑ a b Webmineral - Carnotite (English)
  3. ↑ a b c d Carnotite at mindat.org (engl.)

literature

  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 191 .

Web links

Commons : Carnotite  - collection of images, videos and audio files