Astrocyanite (Ce)

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Astrocyanite (Ce)
Astrocyanite- (Ce) -571090.jpg
Blue astrocyanite (Ce) from the Kamoto East Mine type locality in Kamoto, near Kolwezi , Katanga Province , Democratic Republic of the Congo
General and classification
other names

IMA 1989-032

chemical formula
  • Cu 2+ 4 (Ce, Nd, La) 4 [UO 2 | (OH) 2 | (CO 3 ) 5 ] 2 · 3 (H 2 O)
  • Cu 2 Ce 2 (UO 2 ) (CO 3 ) 5 (OH) 2 · 1.5H 2 O
  • (Ce, Nd) 2 Cu 2+ 2 [UO 2 | (OH) 2 | (CO 3 ) 5 ] · 1.5H 2 O
Mineral class
(and possibly department)
Carbonates and nitrates
System no. to Strunz
and to Dana
5.EF.05 ( 8th edition : V / F.06)
16b.01.06
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-dipyramidal; 6 / m  2 / m  2 / m
Room group (no.) P 6 / mmm (No. 191) (No. 191) Template: room group / 191
Lattice parameters a  = 14.96  Å ; c  = 26.86 Å
Formula units Z  = 12
Physical Properties
Mohs hardness 2 to 3
Density (g / cm 3 ) measured: 3.80; calculated: 3.95
Cleavage good after {0001}
colour light blue, teal
Line color bluish white
transparency translucent to opaque
shine Glass gloss
radioactivity very radioactive
Crystal optics
Refractive indices n ω  = 1.688
n ε  = 1.638
Birefringence δ = 0.050
Optical character uniaxial negative
Pleochroism Strong: light blue to light blue, almost colorless

Astrocyanite- (Ce) is a very rare mineral from the mineral class of " carbonates and nitrates " with the idealized chemical composition Cu 2 Ce 2 (UO 2 ) (CO 3 ) 5 (OH) 2 · 1.5H 2 O and is chemically speaking, it is a water-containing copper - cerium - uranyl carbonate with additional hydroxide ions .

Astrocyanite- (Ce) crystallizes in the hexagonal crystal system , but develops only very small, tabular crystals up to about one millimeter in size, which are often arranged in star- to rosette-shaped mineral aggregates . The translucent to opaque crystals are light blue to blue-green in color and have a glass-like sheen on the surfaces . Astrocyanit- (Ce) leaves a bluish-white line on the marking board .

Etymology and history

Astrocyantite- (Ce) was first described in 1990 by Michel Deliens and Paul Piret . As a general formula for the varying content of rare earth elements (REE = Rare Earth Element (s)), the authors give the formula with Cu 2 (REE) 2 (UO 2 ) (CO 3 ) 5 (OH) 2 1.5 (H 2 O). The name of the mineral is made up of the Greek words for star (άστρον ("astron")) and blue (κυανός ("kyanos")).

The type material of the mineral is in the Muséum des sciences naturelles de Belgique under the catalog no. RC3513 retained .

classification

In the 8th edition of the mineral systematics according to Strunz , which is outdated but still in use , the astrocyanite (Ce) belonged to the common mineral class of “carbonates, nitrates and borates” and there to the division of “uranyl carbonates [UO 2 ] 2+ to [CO 3 ] 2− “, where he formed the unnamed group V / F.06 together with Bijvoetit- (Y) , Kamotoit- (Y) and Shabait- (Nd) .

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 astrocyanite (Ce) to the newly defined class of “carbonates and nitrates”, but also to the “uranyl carbonates” class there " a. This is further subdivided according to the molar ratio of uranium dioxide (UO 2 ) to carbonate complex (CO 3 ), so that the mineral can be found in the sub-section "UO 2  : CO 3  > 1: 1" where it is classified as the only member is the unnamed group 5.EF.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the astrocyanite (Ce) and the outdated Strunz system to the common class of “carbonates, nitrates and borates” and there in the division of “carbonates - hydroxyl or halogen " a. Here he is the only member of the unnamed group 16b.01.06 within the subdivision "Carbonates - Hydroxyl or Halogen with (A) m (B) n (XO 3 ) p Z q , with (m + n): p = 1: 1 ”.

Crystal structure

Astrocyanite- (Ce) crystallizes in the hexagonal crystal system in the space group P 6 / mmm (space group no. 191) with the lattice parameters a  = 14.96  Å (1 Å = 100  pm ) and c  = 26.86 Å as well as 12 formula units per Unit cell . Template: room group / 191

properties

The mineral is very radioactive due to its uranium content of up to 25.0 % by weight . Taking into account the natural decay chains is a for Astrocyanit- (Ce) specific activity of about 45.2 k Bq stated / g (compared to natural potassium 0.0312 kBq / g).

Due to the accompanying rare earth elements, the sum formulas of different mineral samples of astrocyanite (Ce) can differ from one another. For example, in addition to the formula mentioned above, Webmineral also specifies the following formula for the composition: Cu 2 Ce 0.1 Nd 0.6 La 0.2 Pr 0.2 Sm 0.1 (UO 2 ) (CO 3 ) 5 (OH) 2 · 2.7 (H 2 O) The following rare earth elements are found in decreasing frequency as companions in astrocyanite (Ce): Cer (Ce), neodymium (Nd), lanthanum (La), praseodymium (Pr), samarium (Sm) and yttrium (Y).

Education and Locations

Dark green astrocyanite (Ce) and yellowish green kamotoite (Y) from the type locality opencast East Kamoto

Astrocyanite- (Ce) forms as a secondary uranium mineral in the oxidation zone of primary uranium ores.

The mineral is known so far only from the type locality Kamoto East (Kamoto East Open cut) in Kamoto in the Democratic Republic of the Congo . There it is associated with Francoisit- (Nd) , Kamotoit- (Y) , Masuyit , Schuilingit- (Nd) , Shabait- (Nd) and Uranophane . It forms on a dolomitic matrix.

Precautions

Due to the strong radioactivity of the mineral, mineral samples of astrocyanite (Ce) should only be kept in dust- and radiation-tight containers, but especially never in living rooms, bedrooms or workrooms. Likewise, because of the high toxicity and radioactivity of uranyl compounds, absorption into the body ( incorporation , ingestion ) should 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

  • Michel Deliens, Paul Piret, Eddy van der Meersche: Les Mineraux Secondaire d'Uranium du Zaïre. Deuxieme complément . Institut Royal des Sciences Naturelles de Belgique, Brussels 1990, OCLC 28885569 , p. 18 (French).
  • Astrocyanite- (Ce) . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 64 kB ; accessed on March 30, 2018]).

Web links

Commons : Astrocyanite- (Ce)  - collection of images, videos and audio files

Individual evidence

  1. a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  2. a b IMA / CNMNC List of Mineral Names; November 2017 (PDF 1.67 MB)
  3. a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  322 .
  4. a b c d Astrocyanite- (Ce) at Webmineral.com
  5. a b c d e Astrocyanite- (Ce) . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 64  kB ; accessed on March 30, 2018]).
  6. a b c d Mindat - Astrocyanite- (Ce) at Mindat.org
  7. ^ John Leslie Jambor , Jacek Puziewicz: New Mineral Names . In: American Mineralogist . tape  76 , 1991, pp. 665–671 ( minsocam.org [PDF; 830 kB ; accessed on March 30, 2018]).