Dewindtite

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Dewindtite
Dewindtite-571792.jpg
yellow dewindtite from the Kasolo Mine in the Democratic Republic of the Congo
General and classification
other names

Stasite

chemical formula Pb 3 [(UO 2 ) 3 | O | OH | (PO 4 ) 2 ] 2 • 12H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.EC.10 ( 8th edition : 7 / E.07)
42.09.08.01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal, 2 / m 2 / m 2 / m
Space group Bmmb (No. 63, position 6)Template: room group / 63.6
Lattice parameters a  = 16.03  Å ; b  = 17.62 Å; c  = 14.61 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 2.75
Density (g / cm 3 ) measured: 5.03; calculated: 5.12
Cleavage Completely at {100}
Break ; Tenacity brittle
colour canary yellow, partly with a green cast
Line color bright yellow
transparency semi-transparent
shine Resin or wax gloss
radioactivity available
Crystal optics
Refractive indices n α  = 1.760 to 1.762
n β  = 1.767 to 1.768
n γ  = 1.768 to 1.770
Optical character biaxial positive
Axis angle 2V = moderate to large, 30 °
Pleochroism X = colorless, Y = Z = golden yellow
Other properties
Chemical behavior soluble in acids
Special features green fluorescence

Dewindtite is a rare mineral from the mineral class of phosphates , arsenates and vanadates . It crystallizes in the orthorhombic crystal system with the chemical composition Pb 3 [(UO 2 ) 3 | O | OH | (PO 4 ) 2 ] 2 · 12H 2 O and is therefore chemically seen a hydrous lead - uranyl - phosphate with additional oxygen - and Hydroxide ions .

Dewindtite forms tabular crystals along [100] with a size of up to 3 mm. The crystals are fine-grained to massive. Dewindtite is yellow in color. Due to its pleochroism, the color ranges from colorless to canary yellow, depending on the viewing direction. The mineral is translucent and has a resin-like to wax-like sheen on the surface .

Etymology and history

The mineral was discovered in 1922 by Alfred Schoep in a sample from Katanga , Democratic Republic of the Congo and named after the Belgian geologist Dr. Jean Dewindt named, who drowned in Lake Tanganyika (Congo). Schoep discovered in 1923 that the mineral is identical to stasite . The status of dewindtite has long been very unclear. It has been suggested, based on X-ray studies , that the mineral is a mixture of renardite and phosphuranylite . In addition, the chemical composition was not entirely clear. For example, Pb 2 (UO 2 ) 4 (PO 4 ) 3 (OH) 3 · 7H 2 O is also given, based on an X-ray analysis by Hogarth and Nuffield from 1954.

The above formula was redefined in 1990 by Paul Piret, Jacqueline Piret-Meunier and Michel Deliens after more recent analyzes using X-ray diffractometry and corresponds, albeit in a slightly different way, to (H 2 Pb 3 (UO 2 ) 6 O 4 (PO 4 ) 4 12H 2 O) of the formula currently (2015) used by the International Mineralogical Association (IMA).

The type material is kept in the Royal Museum for Central Africa in Tervuren , Belgium (catalog no. RGM6433) and in the Natural History Museum Paris (catalog no. 122.106).

classification

Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the dewindtite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "uranyl phosphates / arsenates and uranyl vanadates", where together with Althupit , Arsenovanmeersscheit , Arsenuranylite , Bergenit , Dumontit , Françoisit- (Ce) , Françoisit- (Nd) , Hügelite , Kamitugait , Kivuit , Metavanmeer log , Mundit , Phosphuranylit , Phuralumit , Phurcalit , Vanmeersscheit and Yingjiangit formed the unnamed group with the system number VII / E.07.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also classifies dewindtite in the category of “uranyl phosphates and arsenates”. However, this is further subdivided according to the ratio of uranyl to anions , so that the mineral can be found according to its composition in the sub-section "UO 2  : RO 4  = 3: 2", where arsenuranylite, phosphuranylite and yingjiangite in the phosphuranylite Phurcalit group with the system number 8.EC.10 is.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns dewindtite to the class of "phosphates, arsenates and vanadates" and there in the section "water-containing phosphates etc., with hydroxyl or halogen " (no. 42) and there in the subgroup “with (A) 3 (XO 4 ) 2 Z q × x (H 2 O)”. Here he is the only one in the unnamed group with the system number 42.09.08 .

Chemism

Theoretically, i.e. in an ideal composition, dewindtite consists of 49.18% uranium , 21.41% lead , 4.27% phosphorus , 0.90% hydrogen and 24.24% oxygen .

Crystal structure

Dewindtite crystallizes orthorhombically in the space group Bmmb (space group no. 63, position 6) with the lattice parameters a  = 16.03  Å , b  = 17.62 Å and c  = 14.61 Å and four formula units per unit cell . Template: room group / 63.6

properties

Chemical properties

Dewindtite is very soluble in acids .

Physical Properties

Due to its uranium content of up to 49.18%, the mineral is very radioactive . Taking into account the natural decay chains or of existing decay products which is specific activity of 88.04 k Bq / g indicated (compared to natural potassium 0.0312 kBq / g). The quoted value can vary significantly depending on the mineral content and the composition of the levels; selective enrichment or depletion of the radioactive decay products is also possible and changes the activity.

Dewindtite shows green fluorescence under short and long-wave UV light.

Education and Locations

Lemon yellow, needle-like dewindtite crystals from Grury , France (image width: approx. 5 mm)

Dewindtite forms as a secondary mineral in the oxidation zone of uraninite or other uranium-containing minerals. It forms communions with torbernite , parsonsite , dumontite, uraninite, bergenite, autunite , barium-containing uranophane , uranosphaerite and wölsendorfite .

88 locations of Dewindtit are known (as of 2015).

The type locality of Dewindtit is in the Democratic Republic of the Congo . In addition to the type locality, it is also known from the Swambo mine in the Congo.

Nine sites are known in Germany . There is a site near Menzenschwand in Baden-Württemberg in the Black Forest . There are three known sites in Bavaria : one in the Fichtel Mountains , a second in Wösendorf and a third in Zandt . In Rhineland-Palatinate, there is also a site near Ellweiler in the Birkenfeld district . In Saxony there is one site in the Ore Mountains near Schneeberg and two sites in Vogtland . A last German site is in Thuringia near Wurzbach .

In Switzerland there are two sites in the canton of Valais : one near Finhaut and one near Les Marécottes .

There are surprisingly many sites in France , which can show 30 sites. They are located in the Auvergne-Rhône-Alpes , Bretagne , Bourgogne-Franche-Comté , Occitania , Nouvelle-Aquitaine , Pays de la Loire and Provence-Alpes-Côte d'Azur regions .

The other sites are in Argentina , Australia , Gabon , Italy , Canada , Colombia , Madagascar , Portugal , Slovenia , Tajikistan , the Czech Republic , the United Kingdom and the United States of America .


Precautions

Due to the toxicity and the high level of radioactivity of the mineral, mineral samples from dewindtite should only be kept in dust- and radiation-tight containers, but especially never in living rooms, bedrooms or workrooms. 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

literature

  • C. Palache, H. Berman, C. Frondel: Dana's system of mineralogy . 7th edition. tape 2 , 1951, p. 875, 928 .
  • Clifford Frondel : Systematic Mineralogy of Uranium and Thorium In: US Geological Survey Bulletin , 1958 ( PDF ).
  • DD Hogarth, EW Nuffielt: Studies of radioactive compounds: VII - Phosphuranylite and dewindtite. In: American Mineralogist , Vol. 39, 1954, pp. 444-447 ( PDF ).
  • Paul Piret, Jacqueline Piret-Meunier, Michel Deliens: Composition chimique et structure cristalline de la dewindtite Pb 3 [H (UO 2 ) 3 O 2 (PO 4 ) 2 ] 2 · 12H 2 O. In: European Journal of Mineralogy , volume 2, 1990, pp. 399-405 doi : 10.1127 / ejm / 2/3/0399 (French with a brief English description).

Web links

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

Individual evidence

  1. ↑ 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.  528 .
  2. ↑ a b c Mineralienatlas: Dewindtit .
  3. ↑ a b c d e f g Mindat - Dewindtit .
  4. ↑ a b c d e f Dewindtite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 59.7 kB ).
  5. ↑ Clifford Frondel : Systematic Mineralogy of Uranium and Thorium In: US Geological Survey Bulletin , 1958 ( PDF ).
  6. ↑ IMA / CNMNC List of Minerals December 2014 (English, PDF).
  7. ↑ a b c Webmineral - Dewindtite