Parsonsite

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Parsonsite
Parsonsite-Torbernite-90912.jpg
Yellow-brown crystals of parsonsite together with dark green torbernite from the Pinhal do Souto mine, Tragos, Chãs de Tavares , Mangualde , Viseu district , Portugal (image width: 4 mm).
General and classification
chemical formula
  • Pb 2 (UO 2 ) (PO 4 ) 2
  • Pb 2 (UO 2 ) (PO 4 ) 2 • 2 (H 2 O)
Mineral class
(and possibly department)
Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana
8.EA.10 ( 8th edition : VII / E.08)
40.02a.31.01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 6.89  Å ; b  = 10.42 Å; c  = 6.68 Å,
α  = 101.43 °; β  = 98.25 °; γ  = 86.28 °
Frequent crystal faces slat-like, elongated in [001], flattened in [010]
Physical Properties
Mohs hardness 2.5 to 3
Density (g / cm 3 ) measured: 5.72 to 5.75; calculated: [6.21]
Cleavage not observed
Break ; Tenacity shell-like, conchoidally indistinct after [010]
colour light yellow, honey-brown, green-brown
Line color White
transparency transparent, opaque
shine Greasy shine
radioactivity radioactive
Crystal optics
Refractive indices n α  = 1.850
n γ  = 1.860 n ω  = 2.150
n ε  = 1.910
Birefringence δ = 0.01
Optical character biaxial negative
Axis angle 2V = 11 ° to 26 °

Parsonsite is a rather seldom occurring mineral from the mineral class of " phosphates, arsenates and vanadates ". It crystallizes in the triclinic crystal system with the idealized chemical composition Pb 2 (UO 2 ) (PO 4 ) 2 . The mineral crystallizes in the form of flattened, pseudo-hexagonal, needle-like mineral aggregates from pale yellow to honey-brown in color.

Etymology and history

Parsonsit was first described in 1923 by Alfred Schoep on a torbernite sample from the Shinkolobwe mine in what is now the Democratic Republic of the Congo. He named it in honor of Arthur Leonard Parsons (1873–1957), Professor of Mineralogy and Petrography at the University of Toronto.

The type material of the mineral is kept at Mines ParisTech in Paris (France).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the parsonsite belonged to the mineral class of "phosphates, arsenates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 hallimondite it belongs to the unnamed group VII /E.08 formed.

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 classifies the parsonsite in the category of "uranyl phosphates and arsenates". However, this is further subdivided according to the molar ratio of the uranyl complex (UO 2 ) to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral can be found in the sub-section "UO 2  : RO 4  = 1: 2" according to its composition is where, together with Hallimondit, the "Parsonsit group" with the system no. 8.EA.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the parsonsite to the class of "phosphates, arsenates and vanadates" and there in the section "water-containing phosphates etc.". Here he is the only member of the unnamed group 40.02a.31 within the subdivision “Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O), with (UO 2 ) 2+ ”can be found.

Crystal structure

Animation of the crystal structure of Parsonsite __ U __ Pb __ O __ P

Parsonsite represents the phosphate analog of the lead uranyl arsenate Hallimondit (Pb 2 (UO 2 ) (AsO 4 ) 2 · nH 2 O, 0 ≤ n ≤ 0.5). In parsonsite crystallizes in the triclinic space group P 1 (space group -No. 2) with the lattice parameters a  = 6.842 (4)  Å , b  = 10.383 (6) Å and c  = 6.670 (4) Å with α = 101.26 (7) ° β = 98.17 (7) ° and γ = 86.38 (7) ° and two formula units per unit cell . Template: room group / 2

The crystal structure analysis of a Parsonsite sample from Grury , France, published by Peter Burns , shows the crystal structure without crystal water ; in contrast, however, the earlier work by Frondel (1958) and Mazzi (1959) as well as laboratory syntheses indicate a varying water of crystallization content of up to two molecules of H 2 O per formula unit. The connectivity of the atoms in parsonsite does not show a layer structure like the autunit layer types and phosphuranylite types known for uranyl phosphates , but three-dimensionally chained pentagonal-bipyramidal uranyl cations and tetrahedral phosphate anions, linked by lead (II) cations.

properties

The mineral is relatively highly radioactive due to its uranium content of up to 26.2 % by weight . Taking into account the natural decay chains is a parsonsite for specific activity of about 46.8 k Bq stated / g (compared to natural potassium 0.0312 kBq / g). The quoted value can vary significantly depending on the mineral content and composition of the levels; selective enrichment or depletion of the radioactive decay products is also possible and changes the activity.

Education and Locations

Parsonsite forms secondarily in the oxidation zone of hydrothermal uranium deposits. It is found associated with torbernite , kasolite , dewindtite ( Shinkolobwe Mine , Democratic Republic of the Congo), autunite , phosphuranylite ( Ruggles Mine , New Hampshire, USA), pyromorphite , torbernite and autunite (Lachaux, France).

Parsonsite is relatively widespread, but is rarely found in good crystals. In Germany, Parsonsit was found in the Krunkelbach mine near Menzenschwand in Baden-Württemberg, the Johannesschachte mine near Wölsendorf in Bavaria, near Ellweiler in Rhineland-Palatinate, the Himmelfahrt mine near Steinbach (Johanngeorgenstadt) , in the forest shaft (shaft 26) near Neustädtel ( Schneeberg) and found near Tirpersdorf in Saxony as well as in the Henneberg quarry near Weitisberga in Thuringia. In Austria, the mineral occurs on the Radhausberg .

Other sites include the Ranger uranium mine in Australia, Jáchymov (St Joachimsthal), Špindlerův Mlýn (Spindleruv Mlyn) and Javorník (Jauernig) in the Czech Republic, in the regions of Auvergne-Rhône-Alpes , Bretagne , Bourgogne-Franche- Comté , Occitania and Nouvelle-Aquitaine in France, Piedmont and Sardinia in Italy, in Miedzianka (Kupferberg) in Poland, in District Guarda and District Viseu in Portugal, and in Arizona , Colorado , Connecticut and New Hampshire in the USA.

Precautions

Due to the toxicity and the strong radioactivity of the mineral, mineral samples from Parsonsite should only be kept in dust- and radiation-proof 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

Web links

Individual evidence

  1. a b c d e f Peter C. Burns: A new uranyl phosphate chain in the structure of parsonsite . In: American Mineralogist . tape 85 , 2000, pp. 801–805 ( rruff.info [PDF; 126 kB ]).
  2. a b c d e f g h i j k l m n o p q r Mindat - Parsonsite
  3. ^ A b Alfred Schoep: Sur la parsonsite, nouveau minéral radioactif . In: Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences . tape 176 , 1923, pp. 171–173 ( rruff.info [PDF; 175 kB ]).
  4. a b c Webmineral - Parsonsite
  5. Mindat - Hallimondite
  6. Parsonsite . 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; 65  kB ]).
  7. a b List of localities for Parsonsite in the Mineralienatlas and in Mindat