Bergenite

from Wikipedia, the free encyclopedia
Bergenite
Bergenite-144917.jpg
Bergenite crystals from shaft 362 near Mechelgrün ( Neuensalz municipality ), Saxony (field of view: 7 mm)
General and classification
chemical formula (Ba, Ca) 2 (OH) 2 [(UO 2 ) 3 | (OH) 2 | (PO 4 ) 2 ] • 5.5H 2 O
Mineral class
(and possibly department)
Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana
8.EC.40 ( 8th edition : VII / E.07)
April 42, 05.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / c (No. 14)Template: room group / 14
Lattice parameters a  = 23.32  Å ; b  = 17.19 Å; c  = 20.63 Å
β  = 93.0 °
Formula units Z  = 18
Physical Properties
Mohs hardness 2-3
Density (g / cm 3 ) measured: ~ 4.1; calculated: 4.98
Cleavage Please complete!
colour yellow
Line color light yellow
transparency translucent
shine Please complete!
radioactivity very strong
Crystal optics
Refractive indices n α  = 1.660
n β  = 1.700 to 1.710
n γ  = 1.722
Birefringence δ = 0.062
Optical character biaxial negative

Bergenite is a very rarely occurring mineral from the mineral class of " phosphates , arsenates and vanadates ". It crystallizes in the monoclinic crystal system with the composition (Ba, Ca) 2 (OH) 2 [(UO 2 ) 3 | (OH) 2 | (PO 4 ) 2 ] · 5.5H 2 O, so it is chemically complex , water-containing uranyl phosphate. The elements barium and calcium indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral.

Bergenite is translucent and usually develops thin tabular to needle-like crystals with a yellow to greenish-yellow color with a light yellow streak .

Etymology and history

Bergenite was first discovered in 1956 on a dump near Streuberg in the municipality of Bergen in the Saxon Vogtland district and described in 1959 by Hans Wilhelm Bültemann and Günter Harald Moh, who named the mineral after its type locality Bergen.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , bergenite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "uranyl phosphates and uranyl vanadates", where together with althupit , arsenovanmeersscheit , arsenuranylite , dewindtite , Dumontit , Françoisit- (Ce) , Françoisit- (Nd) , Hügelite , Kamitugait , Kivuit , Metavanmeer log , Mundit , Phosphuranylit , Phuralumit , Phurcalit , Vanmeersscheit and Yingjiangit formed the independent group VII / E.07 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns bergenite to the class of “phosphates, arsenates and vanadates” and there to the department of “uranyl phosphates and arsenates”. However, this is further subdivided according to the molar ratio of the uranium oxide (UO 2 ) to the phosphate or arsenate complex (RO 4 ), so that the mineral can be found in the sub-section "UO 2  : RO 4  = 3: 2" according to its composition , where it is the only member of the unnamed group 8.EC.40 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns bergenite to the class of "phosphates, arsenates and vanadates" and there to the category of "water-containing phosphates, etc., with hydroxyl or halogen ". Here he is together with Dumontit and Hügelit in the "Dumontit group" with the system no. April 42, 2005 within the subsection of " Water-containing phosphates etc., with hydroxyl or halogen with (AB) 5 (XO 4 ) 2 Z q × x (H 2 O) ".

Crystal structure

Linking pattern of the edge-sharing hexagonal-bipyramidal and pentagonal-bipyramidal uranyl units in bergenite. __ U __ O __ P

Bergenite crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a  = 23.32  Å ; b  = 17.19 Å; c  = 20.63 Å and β = 93.0 ° and 18 formula units per unit cell . The crystal structure of bergenite contains both pentagonal-bipyramidal and hexagonal-bipyramidal uranyl units. In addition, further coordination takes place via phosphate tetrahedra, which are responsible for the formation of the layer structure. These layers are finally coordinated and held together by the calcium and barium ions via the oxygen atoms of the phosphate and uranyl ions. Template: room group / 14

properties

The mineral is classified as very radioactive due to its uranium content of up to 43.28% and has a specific activity of around 77.475 k Bq / g (for comparison: natural potassium 31.2 Bq / g).

Under UV light , some bergenites show a light green fluorescence .

Education and Locations

Nothing is known about the exact formation conditions of bergenite. Uranocircite , torbernite , autunite , dewindtite ( Renardite ) and barium uranophane were found as accompanying minerals .

As a very rare mineral formation, bergenite has so far (as of 2012) only been detected in a few samples from around 10 sites. In addition to its type locality Streuberg near Bergen, the mineral was also found in Germany in “Schacht 362” near Mechelgrün in the Vogtland, near Johanngeorgenstadt and in the “Father Abraham” mine near Lauta in the Ore Mountains and in the Krunkelbach uranium deposit near the Menzenschwand community in Baden-Württemberg .

Bergenite was also found in the "Les Montmins Mine" near Échassières in the French department of Allier and on the Green River in the US state of Utah.

Precautions

Due to the strong radioactivity of the mineral, mineral samples from bergenite should only be kept in dust- and radiation-tight containers, but especially never in living rooms, bedrooms or work rooms. Absorption into the body ( incorporation ) should also be prevented in any case and direct body contact should be avoided to be on the safe side and face masks and gloves should be worn when handling the mineral.

See also

literature

  • Hans W. Bültemann, Günter H. Moh: Bergenite, a new mineral of the phosphuranylite group . In: New yearbook for mineralogy - monthly books . tape 10 , 1959, pp. 232–233 ( minsocam.org [PDF; 220 kB ]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 656 (first edition: 1891).

Web links

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

Individual evidence

  1. a b c d e 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.  528 .
  2. a b c Webmineral - Bergenite (English)
  3. a b Bergenite . 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 August 19, 2017]).
  4. a b c d e f g Mindat - Bergenite (English)
  5. ^ Andrew J. Locock, Peter C. Burns: The crystal structure of bergenite, a new geometrical isomer of the phospuranylite group . In: The Canadian Mineralogist . tape 41 , 2003, p. 91–101 ( rruff.info [PDF; 955 kB ; accessed on August 19, 2017]).