Gauthierite
| Gauthierite | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 2016-004 |
| chemical formula |
|
|
Mineral class (and possibly department) |
Oxides and hydroxides |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | P 2 1 / c (No. 14) |
| Lattice parameters |
a = 29.844 (2) Å ; b = 14.5368 (8) Å; c = 14.0406 (7) Å β = 103.708 (6) ° |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 3-4 |
| Density (g / cm 3 ) | 5.437 (calculated) |
| Cleavage | perfect {010} |
| Break ; Tenacity | uneven |
| colour | orange |
| Line color | bright orange |
| transparency | transparent (single crystals), translucent (solid) |
| shine | Glass gloss |
| radioactivity | highly radioactive |
| Crystal optics | |
| Refractive indices |
n α = 1.780 (5) n β = 1.815 (5) n γ = 1.825 (5) |
| Optical character | biaxial negative |
| Axis angle | 2V = 58 (1) ° (measured); 58.4 ° (calculated) |
Gauthierit is a very rarely occurring minerals from the mineral class of oxides and hydroxides having the idealized chemical composition KPb [(UO 2 ) 7 O 5 (OH) 7 ] ∙ 8H 2 O and chemical point of a crystal water-containing potassium - and lead-containing uranyl - oxide - hydroxide .
Gauthierite crystallizes in the monoclinic crystal system and is found in the form of orange tablets up to 1 mm in length. The mineral is transparent to translucent and has a grease-like sheen on the surface . So far it is only known from a single source.
Etymology and history
Gauthierite is a very rare mineral and was first described in 2017. It was on an old mineral level from the Shinkolobwe mine ( Democratic Republic of Congo discovered). One of the co-authors of the study got it from the Belgian mineral collector Gilbert Joseph Gauthier (December 24, 1924 - June 23, 2006), who mainly collected uranium minerals, and named it after him. There are very few mineral samples of gauthierite in the world as there is no new material from active mineral developments. All known gauthierite samples are on old collection levels, most of which are in private collections. Due to the small size of the crystals, many old mineral grades would have to be re-analyzed and determined by the owners in order to verify or rule out that they also show gauthierite crystals.
classification
Since the gauthierite was only described as an independent mineral in 2017, it is neither listed in the 8th edition , which has been outdated since 1977, nor in the 9th edition of the mineral systematics according to Karl Hugo Strunz . The mineral system of minerals according to Dana , which is mainly used in the English-speaking world , is also unknown to date.
Only in the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on the old form of the systematics by Karl Hugo Strunz in the 8th edition, the mineral received the system and mineral number IV / H.07-35 . In the Lapis-system equivalent to the class of oxides and hydroxides, where the Department of uranyl ([UO 2 ] 2+ ) hydroxides and hydrates where Gauthierit with Curit , Fourmarierit , Metavandendriesscheit , Richetit , Sayrit , Spriggit , Shinkolobweit and Vandendriesscheit forms an independent but unnamed group (as of 2018).
Chemism
The electron beam microanalysis on a total of nine samples of the type material from the Shinkolobwe mine resulted in an average composition with a mass fraction of 1.29% by weight K 2 O , 7.17% by weight PbO , 82.10% by weight UO 3 and 8.78 wt .-% H 2 O .
On the basis of 34 oxygen atoms (apfu), this results in the empirical formula K 0.67 Pb 0.78 U 7 O 34 H 23.77 , which results in KPb [(UO 2 ) 7 O 5 (OH) 7 ] ∙ 8H 2 O was idealized.
Crystal structure
Gauthierite crystallizes monoclinically in the space group P 2 1 / c (space group no. 14) with the lattice parameters a = 29.844 (2) Å ; b = 14.5368 (8) Å and c = 14.0406 (7) Å and β = 103.708 (6) ° as well as eight formula units per unit cell .
The crystal structure of gauthierite is related to that of Vandendriesscheit . Together with fourmarierite , the three minerals form a group of early transformation products of the weathering and hydration of uraninite . They are characterized by a high proportion of crystal water between the crystallographic uranyl layers.
properties
Due to its uranium content of up to 67.2%, the mineral is radioactive in terms of the ideal formula . Considering that natural uranium has a specific activity of about 50 kBq / g, can be used for the mineral has a specific activity of about 33.6 k Bq / g are calculated (compared to natural potassium 0.0312 kBq / g). However, the absolute radioactivity of real mineral samples can be increased if the matrix contains uraninite and / or daughter products from the decay series.
Education and Locations
So far, gauthierite could only be detected on old collection samples from its type locality , the Shinkolobwe mine in the Democratic Republic of the Congo (as of 2021). The mineral is associated with soddyite , slodovskite and the members of the metazeunerite - metatorbernite - mixed crystal series . The matrix is quartz mixed with aged uraninite. Gauthierite is presumably formed through weathering of uraninite in the presence of radiogenic lead, while potassium is added through leaching processes from other gangue minerals.
Precautions
Due to the toxicity and the strong radioactivity of the mineral, mineral samples of gauthierite should only be kept in dust and radiation-proof containers, but especially never in living rooms, bedrooms or work rooms. 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
- Travis A. Olds, Jakub Plášil, Anthony R. Kampf, Radek Škoda, Peter C. Burns, Jiří Čejka, Vincent Bourgoin and Jean-Claude Boulliard: Gauthierite, KPb [(UO 2 ) 7 O 5 (OH) 7 ] · 8H 2 O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology . In: European Journal of Mineralogy . tape 29 , no. 1 , 2017, p. 129–141 , doi : 10.1127 / ejm / 2017 / 0029-2586 (English).
- Gauthierite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2018 (English, handbookofmineralogy.org [PDF; 346 kB ; accessed on April 4, 2021]).
Web links
- Gauthierite. In: Mineralienatlas Lexikon. Stefan Schorn et al., Accessed on April 4, 2021 .
Individual evidence
- ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2021. (PDF; 3.5 MB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2021, accessed April 5, 2021 .
- ↑ a b c d e f g h i j k l m Travis A. Olds, Jakub Plášil, Anthony R. Kampf, Radek Škoda, Peter C. Burns, Jiří Čejka, Vincent Bourgoin and Jean-Claude Boulliard: Gauthierite, KPb [ (UO2) 7 O5 (OH) 7] · 8H2 O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology . In: European Journal of Mineralogy . tape 29 , 2017, p. 129–141 (English, [1] [PDF; 968 kB ; accessed on October 14, 2020]).
- ↑ 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 .