Weeksit

from Wikipedia, the free encyclopedia
Weeksit
Weeksite.jpg
Yellow weeksite crystals from Goanikontes, Namibia (image width 5 mm)
General and classification
other names
  • ICSD 63515
chemical formula
  • K 2 (UO 2 ) 2 (Si 2 O 5 ) 3 · 4H 2 O
  • K 1.26 Ba 0.25 Ca 0.12 [(UO 2 ) 2 (Si 5 O 13 )] · H2O
  • K 2 (UO 2 ) 2 (Si 5 O 13 ) • 4H 2 O
Mineral class
(and possibly department) 		Silicates and germanates - layered silicates (phyllosilicates)
System no. to Strunz
and to Dana 		9.AK.30 ( 8th edition : VIII / A'.15)
53.03.02.01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 14.1957 (4)  Å ; b  = 14.2291 (5) Å; c  = 9.6305 (3) Å
α  = 90; β  = 111.578 (3); γ  = 90 Please complete the source as an individual reference!
Physical Properties
Mohs hardness 1 to 2
Density (g / cm 3 ) 4.1
Cleavage good after {hk0}
colour yellow
Line color yellow
transparency transparent to translucent
shine waxy, silky
radioactivity very strong with 86.96 k Bq / g
Crystal optics
Refractive indices n α  = 1.596
n β  = 1.603
n γ  = 1.606
Birefringence δ = δ = 0.010
Optical character biaxial negative
Axis angle 2V = 60 ° (measured); 66 ° (calculated)
Pleochroism x: colorless, y: pale yellow-green, z: yellow-green
Other properties
Chemical behavior soluble in acids

Weeksite is a rarely occurring mineral from the mineral class of "silicates and germanates" with the chemical composition K 2 (UO 2 ) 2 (Si 5 O 13 ) · 4H 2 O an. and chemical terms, a water-containing potassium - uranyl - silicate with additional hydroxide . The mineral often contains traces of barium and calcium . A possible empirical formula for this is K 1.26 Ba 0.25 Ca 0.12 [(UO 2 ) 2 (Si 5 O 13 )] H 2 O.

Weeksit crystallizes in the orthorhombic crystal system and develops soft, non-fluorescent lance-like crystals , but mainly radial mineral aggregates of yellow color. The surfaces of the translucent crystals show a waxy to silk-like sheen .

Etymology and history

Weeksit was named in 1960 after Mary Alice Dowse Weeks (1909–1988), who was a mineralogist with the US Geological Survey and who specialized in uranium and vanadium minerals. He was in the Thomas Range at Autunite No. 8 Claim, discovered in Juab County , Utah, USA.

classification

In the now outdated 8th edition of the mineral classification according to Strunz , the Weeksit belonged to the mineral class of "silicates and Germanates" and there to the department of "Neso-Subsilicates", where together with Haiweeit it belonged to the "Weeksit Group ", which belongs to the uranyl silicate family “With the system no. VIII / A'.15 formed.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. VIII / H.37-10 . In the "Lapis system" this also corresponds to the class "Silicates and Germanates", but there the department "Layered silicates", where Weeksit together with Coutinhoit , Haiweeit and Metahaiweeit forms an independent but unnamed group.

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, again classifies the Weeksit under the category of "island silicates (nesosilicates)". This is further subdivided according to the possible presence of further anions, the structure or the molar ratio of uranium:  silicon . Accordingly, Weeksit can be found in the department of "Uranyl island and polysilicates with the molar ratio U: Si = 2: 1", where together with Coutinhoit it is the "Weeksit group" with the system no. 9.AK.30 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Weeksit to the class of "silicates and germanates" and there in the section of "island silicates: SiO 4 groups and other anions of complex cations". Here he is together with Coutinhoit, Haiweeit and Meta-Weeksit in the "Weeksit group" with the system no. 53.03.02.01 to be found in the subsection “Island silicates with SiO 4 groups and other anions as well as complex cations with (UO 2 ) ”.

Crystal structure

In the first description, Weeksit is described as orthorhombic and pseudotetragonal with the space group space group Pnna (space group no. 52) and the cell parameters a  = 14.26 (2)  Å ; b  = 35.88 (10) Å and c  = 14.20 (2) Å. The authors give K 2 (UO 2 ) 2 (Si 2 O 5 ) 3 · 4H 2 O as the sum formula . Template: room group / 52

Jackson and Burns re-examined the structure in 2001 and describe Weeksite as a mineral that is orthorhombic in the space group Cmme (space group no. 67, position 2) with the lattice parameters a  = 14.209 (2)  Å ; b  = 14.248 (2) Å and c  = 35.869 (4) Å as well as 4 formula units per unit cell crystallizes. The authors describe the examined mineral with the formula K 1.26 Ba 0.25 Ca 0.12 [(UO 2 ) 2 (Si 5 O 13 )] H 2 O. Template: room group / 67.2

In 2012 a new investigation could show that the investigation from 2001, which describes the mineral as orthorhombic, is a result of twinning, and the mineral in the space group C 2 / m (space group no. 12) with the cell parameters a  = 14.1957 (4)  Å ; b  = 14.2291 (5) Å, c  = 9.6305 (3) Å and β = 111.578 (3) °, V = 1808.96 (10) Å 3 crystallized. You give the ideal empirical formula as K 2 (UO 2 ) 2 (Si 5 O 13 ) · 4H 2 O. Template: room group / 12

properties

The mineral is very radioactive due to its uranium content of over 52.8% . Taking into account the proportions of the radioactive elements in the idealized empirical formula and the Folgezerfälle of the natural decay chains a specific activity of approximately 86.96 k for the mineral Bq stated / g (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.

Education and Locations

Weeksit is found as a secondary mineral in the oxidation zone of uranium deposits . In its type locality it occurs in opal-containing veins in rhyolite and agglomerates, as well as in sandstones and limestones. As Begleitminerale occur among others opal, chalcedony, calcite, gypsum, fluorite, uraninite, thorogummite, Uranophan, Boltwoodit, Carnotit and Margaritasit.

Only a small number of places where the Weeksite was found are known, including: Flinders Ranges, Australia, Fresach, Austria, Minas Gerais and São Paulo, Brazil, Quebrada San Miguel, Chile, Mariánské Lázně, Jáchymov and Nepomuk, Czech Republic, Menzenschwand und Dörrmorsbach, Germany, Ningyo-toge mine, Japan, Sierra Peña Blanca, Mexico, Goanikontes, Namibia, Macusani Uranium Deposits (Quenamari Meseta), Peru, Crucea, Romania and in the states of Arizona, California, Nevada, New Mexico, Pennsylvania, Texas, Utah, and Wyoming in the United States.

Precautions

Due to the radioactivity of the mineral, mineral samples from Weeksit should only be kept in dust- and radiation-proof containers, but especially never in living rooms, bedrooms or work rooms. 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 respiratory protection mask and gloves should be worn when handling the mineral .

See also

Web links

Commons : Weeksite  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l David Barthelmy: Weeksite Mineral Data. In: webmineral.com. Retrieved June 8, 2020 .
  2. ^ A b WF Outerbridge, MH Staatz, R. Meyrowitz and AM Pommer: Weeksite, a new uranium silicate from the Thomas Range, Juab County, Utah . In: The American Mineralogist . tape 45 , 1960, pp. 39–52 (English, minsocam.org [PDF; 922 kB ; accessed on June 8, 2020]).
  3. ↑ a b c Jennifer M. Jackson and Peter C. Burns: A re-evaluation of the structure of weeksite, a URANYL SILICATE FRAMEWORK MINERAL . In: The American Mineralogist . tape 39 , 2001, p. 187–195 (English, web.gps.caltech.edu [PDF; 1000 kB ; accessed on June 8, 2020]).
  4. ↑ a b c d e f g h i j Karla Fejfarová, Jakub Plášil, Hexiong Yang, Jiří Čejka, Michal Dušek, Robert T. Downs, Madison C. Barkley, Radek Škoda: Revision of the crystal structure and chemical formula of weeksite, K 2 (UO 2 ) 2 (Si 5 O 13 ) · 4H 2 O . In: American Mineralogist . tape 97 , 2012, p. 750-754 , doi : 10.2138 / am.2012.4025 (English).
  5. ↑ a b c d e f g Weeksite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 8, 2020 .
  6. ↑ a b Weeksite . 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; 204  kB ; accessed on June 8, 2020]).
  7. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  8. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed September 14, 2019 .
  9. ↑ The former name of this space group was Cmmb .