Metanatroautunit

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Metanatroautunit
General and classification
chemical formula Na 2 [UO 2 | PO 4 ] 2  • 8H 2 O

or
Na 2 (UO 2 ) 2 (PO 4 ) 2  • 6−8 H 2 O

Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.EB.10 ( 8th edition : VII / E.02)
40.02a.05.01
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal 4 / m 2 / m 2 / m
Space group P 4 / nmm
Lattice parameters a  = 6.92  Å ; c  = 8.63 Å
Formula units Z  = 1
Physical Properties
Mohs hardness 2.0 to 2.5
Density (g / cm 3 ) calculated: 3.62
Cleavage completely after {001}, almost completely after {100}
colour lemon yellow
Line color pale yellow
transparency translucent
shine Glass gloss, pearlescent
radioactivity radioactive
Crystal optics
Refractive indices n ω  = 1.578
n ε  = 1.559
Birefringence δ = 0.019
Optical character uniaxial negative
Pleochroism weak: ω = ε = light yellow

Metanatroautunit , also Meta-Natroautunit , Meta-Sodium-Autunit or Sodium Meta-Autunit (English: Metanatroautunite or Sodium meta-autunite ; formerly Sodium Autunit or Natroautunite ) is a very rarely occurring mineral from the class of " phosphates , arsenates and Vanadates ". It crystallizes in the tetragonal crystal system with the chemical composition Na 2 [UO 2 | PO 4 ] 2  • 8H 2 O or Na 2 (UO 2 ) 2 (PO 4 ) 2  • 6−8 H 2 O.

Metanatroautunit thus represents the sodium analog of autunite (Ca [UO 2 | PO 4 ] 2  • 10–12H 2 O) with a lower water of crystallization content ( Meta ) and, similar to this, develops mostly tabular crystals up to about 5 mm in size and radial, leafy ones Mineral aggregates from lemon-yellow to greenish-yellow color with light yellow streak color .

Special properties

The mineral is classified as very radioactive due to its uranium content of up to 51.7% and has a specific activity of around 92.6 k Bq / g (for comparison: natural potassium 31.2 Bq / g).

Under UV light , some show a yellowish-green fluorescence , similar to that of neon-colored highlighters .

Etymology and history

The mineral was first discovered in the uranium deposit “Kuruk” near Khodzhent in the Tajik province of Sughd . It was described in 1957 by AA Chernikov, OV Krutetskaya and NI Organova, who initially referred to it as Natroautunit with the formula Na (UO 2 ) (PO 4 ) • 5-8H 2 O based on its composition and thus close relationship to the autunit . In a further publication from 1994 in the Doklady Akademiia Nauk , the research team around Chernikov once again dealt with the natroautunite and metanatroautunite , which ultimately led to an application for a redefinition and renaming of the mineral.

In 2004 the application was approved by the "CNMMN", a commission of the International Mineralogical Association (IMA) for the naming and classification of new minerals, and the mineral was renamed Metanatroautunit. The formula has been corrected to Na 2 (UO 2 ) 2 (PO 4 ) 2  • (6−8) H 2 O.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the metanatroautunit belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the general department of "uranyl phosphates and uranyl vanadates", where together with Autunit, Fritzscheit , Heinrichit , Kahlerite , Nováčekit , Sabugalit , Saléeit , Torbernit , Trögerit , Uranocircit , Uranospinit and Zeunerit formed an independent group.

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the IMA, also assigns the metanatroautunit to the class of "phosphates, arsenates and vanadates" and the department of "uranyl phosphates and arsenates". However, this section is now more precisely subdivided according to the molar ratio of uranium oxide complex (UO 2 ): phosphate or arsenate complex (RO 4 ), so that the mineral can be found in the sub-section "UO 2  : RO 4  = 1: 1" according to its composition where it together with Bassetit , Lehnerit , meta-autunite , Metaheinrichit , Metakahlerit , Metakirchheimerit , Metalodèvit , Metanováčekit , Metasaléeit , Metatorbernit , Metauramphit , Metauranocircit I , Metauranocircite II , Metauranospinit , Metazeunerit , Przhevalskit and Uramarsit the unnamed group 8.EB.10 forms.

The systematics of minerals according to Dana also assigns the metanatroautunit to the class of "phosphates, arsenates and vanadates" and there into the department of "hydrated phosphates etc.". Here he is the only member of the unnamed group 40.02a.05 within the subdivision of “ Hydrated Phosphates etc., with A ++ (B ++ ) 2 (XO 4 ) • x (H 2 O), with (UO 2 ) + + "

Education and Locations

Metanatroautunite forms, mostly in paragenesis with schoepite , gypsum , kaolinite and limonite , in the oxidation zone of uranium deposits in granodiorites .

In addition to its type locality "Kuruk" (Khodzhent, Sughd) in Tajikistan , the mineral could also be found in the granite quarries at Lake Boga (Victoria) and at Boomerang Lake near Menangina ( Western Australia ) in Australia as well as in the Cave Hills , North Cave Hills and Slim Buttes in Harding County, South Dakota, USA.

Crystal structure

Metanatroautunit crystallizes tetragonally in the space group P 4 / nmm with the lattice parameters a  = 6.92  Å and c  = 8.63 Å and one formula unit per unit cell .

Metanatroautunit differs from the “normal” autunit only in that one calcium atom in the molecule is replaced by two sodium atoms. There is also a little less water of crystallization .

Precautions

Due to the damage to health caused by ingesting small particles into the body, hands should be washed after contact with the material.

See also

Individual evidence

  1. ↑ 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. 524 .
  2. ↑ IMA / CNMNC List of Mineral Names - Metanatroautunite (English, PDF 1.8 MB; p. 187)
  3. ↑ a b Webmineral - Sodium-autunite (English)
  4. ↑ Handbook of Mineralogy - Sodium meta-autunite (English, PDF 65.9 kB)
  5. ↑ a b c Metanatroautunite at mindat.org (engl.)
  6. ↑ a b IMA / CNMNC List of Mineral Names - Natroautunite discredited (English, PDF 1.8 MB; p. 199)
  7. ↑ Mineral Names, Redefinitions & Discreditations Passed by the CNMMN of the IMA - Metanatroautunite (p. 94) and Natroautunite (p. 99) (PDF; 703 kB)
  8. ^ 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. 524 .

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