{{Short description|Hydrous oxyuranyl mineral}} {{Infobox mineral | name = Gauthierite | category = Oxide mineral | boxwidth = | boxbgcolor = | image = Gauthierite assembly.jpg | imagesize = 260px | caption = Gauthierite crystals from Shinkolobwe Mine; approximate field of view {{cvt|3|mm}} | formula = * idealised: {{chem2|KPb[(UO2)7O5(OH)7]*8H2O}}<ref name="Olds" /><ref name="IMA-Liste-2021-03" /> * empirical: K0.67 Pb0.78 U7 O34 H23.77<ref name="Olds" /> | IMAsymbol = Gut<ref name="Warr" /> | molweight = | strunz = 4.GB | system = Monoclinic | class = 2/''m''<ref name="Olds" /> | symmetry = ''P''2<sub>1</sub>/''c''<ref name="Olds" /> | color = orange<ref name="Olds" /> | habit = Tabular crystals | twinning = | cleavage = Perfect [010] | fracture = Uneven | mohs = 3–4 | luster = Glassy<ref name="Olds" /> | refractive = nα = 1.780(5) nβ = 1.815(5) nγ = 1.825(5)<ref name="Olds" /> | opticalprop = Biaxial (-) | birefringence = | pleochroism = x: very pale yellow, y = z = orange-yellow | streak = Light orange | density = calculated: 5.437<ref name="Olds" /> | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent (single crystals), translucent (masses) | other = 25px Radioactive | references = }}
'''Gauthierite''' is a very rare mineral with the idealised chemical sum formula {{chem2|KPb[(UO2)7O5(OH)7]*8H2O}}.<ref name="Olds" /> It is a radioactive, hydrated orange-coloured lead potassium uranyl oxide hydroxide. It was found by analysing old mineral specimens, and is only known from one locality, the Shinkolobwe Mine in the Democratic Republic of the Congo. The mineral was named in honour of Gilbert Gauthier,<ref>{{Cite journal |last=King |first=Vandall T. |date=2006 |title=Obituary: Gilbert Gauthier |url=https://www.thefreelibrary.com/Died%2C+Gilbert+Gauthier%2C+81.-a0152633241 |journal=The Mineralogical Record |volume=37 |issue=5 |pages=354–355 |access-date=2023-08-28 |archive-date=2023-08-28 |archive-url=https://web.archive.org/web/20230828232407/https://www.thefreelibrary.com/Died%2C+Gilbert+Gauthier%2C+81.-a0152633241 |url-status=live }}</ref> a Belgian collector of uranium minerals, who provided a sample to one of the co-authors of the study that first identified it in 2017.<ref name="Olds" />
== Etymology and history == thumb|left|Gauthierite crystals on matrix (field of view app. 3 mm) Gauthierite is a very rare mineral and was first described in 2017. It was discovered on an old mineralogical sample from Shinkolobwe Mine, Democratic Republic of the Congo.<ref name="Olds" /> A co-author of the original study was given the sample by Gilbert Joseph Gauthier (24. December 1924 – 23. June 2006), a Belgian mineral collector who focused on uranium minerals, after whom the mineral was named.<ref name="Olds" />
== Classification == According to the International Mineralogical Association (IMA), which last updated its list in 2009,<ref name="IMA-Liste-2021-03" /> the Nickel-Strunz system lists gauthierite in the section of "oxides and hydroxides" amongst the "uranyl hydroxides".<ref name="Olds"/> There it forms the group 4.GB, together with leesite K(H<sub>2</sub>O)<sub>2</sub>[(UO<sub>2</sub>)<sub>4</sub>O<sub>2</sub>(OH)<sub>5</sub>]·3H<sub>2</sub>O, shinkolobweite Pb<sub>1.25</sub>[U<sup>5+</sup>(H<sub>2</sub>O)<sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>5</sub>O<sub>8</sub>(OH)<sub>2</sub>](H<sub>2</sub>O)<sub>5</sub> and kroupaite KPb<sub>0.5</sub>[(UO<sub>2</sub>)<sub>8</sub>O<sub>4</sub>(OH)<sub>10</sub>]·10H<sub>2</sub>O.<ref name="Olds"/>
== Chemistry == An analysis by electron microprobe using nine samples of the type material gave an averaged composition of 1.29 w.-% K<sub>2</sub>O, 7.17 w.-% PbO, 82.10 w.-% UO<sub>3</sub> and 8.78 w.-% H<sub>2</sub>O. Based on 34 oxygen atoms this gives the empirical sum formula K<sub>0.67</sub>Pb<sub>0.78</sub>U<sub>7</sub>O<sub>34</sub>H<sub>23.77</sub>, which is idealised as KPb[(UO<sub>2</sub>)<sub>7</sub>O<sub>5</sub>(OH)<sub>7</sub>]∙8H<sub>2</sub>O.<ref name="Olds" />
thumb|left|Gauthierite single crystal (app. 0.1 mm) Gauthierite crystallises monoclinically in space group ''P''2<sub>1</sub>/''c'' 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)° with eight formula units per unit cell. <ref name="Olds" /> The crystal structure is related to that of vandendriesscheite. Together with fourmarierite these three minerals form a group of early stage alteration products which are formed in the oxidation-hydration weathering of uraninite. This is particularly prominent in the amount of water between the uranyl layers.<ref name="Olds" />
Because of its uranium content of about 67.2% the material is strongly radioactive.<ref>{{cite journal |last1=Lu |first1=Kimbal T. |last2=Zhang |first2=Yingjie |last3=Wei |first3=Tao |last4=Ablott |first4=Timothy A. |last5=Plášil |first5=Jakub |last6=Karatchevtseva |first6=Inna |last7=Zheng |first7=Rongkun |title=Investigation of uranium oxide hydrates with barium(II) ions: structural diversity, uranium valences and implications |journal=New Journal of Chemistry |date=2023 |volume=47 |issue=28 |pages=13286–13296 |doi=10.1039/D3NJ01334K|s2cid=259745427 |doi-access=free }}</ref>
== Occurrence and localities == Gauthierite has so far been only identified on old mineralogical samples from its type locality Shinkolobwe Mine in the Democratic Republic of the Congo. The mineral is associated on the type specimen with soddyite, sklodowskite and a member of the metazeunerite-metatorbernite series. The matrix of the type material is quartz with disseminated altered uraninite. The mineral may form by weathering of uraninite in the presence of radiogenic lead, while potassium may be leached from other gangue materials.<ref name="Olds" />
== See also == * List of minerals * List of minerals named after people
==References== <references>
<ref name="IMA-Liste-2021-03">M. Back, W. D. Birch, M. Blondieau et al.: ''The New IMA List of Minerals – A Work in Progress – Updated: March 2021'' [http://cnmnc.main.jp/IMA_Master_List_%282021-03%29.pdf PDF 3.5 MB] {{Webarchive|url=https://web.archive.org/web/20230828232437/http://cnmnc.main.jp/IMA_Master_List_%282021-03%29.pdf |date=2023-08-28 }})</ref> <ref name="Warr">L. Warr: ''IMA–CNMNC approved mineral symbols'' In: ''Mineralogical Magazine'' 2021, ''85'', 291–320 ([https://www.cambridge.org/core/services/aop-cambridge-core/content/view/62311F45ED37831D78603C6E6B25EE0A/S0026461X21000438a.pdf/imacnmnc-approved-mineral-symbols.pdf cambridge.org PDF 320 kB] {{Webarchive|url=https://web.archive.org/web/20230828232410/https://www.cambridge.org/core/services/aop-cambridge-core/content/view/62311F45ED37831D78603C6E6B25EE0A/S0026461X21000438a.pdf/imacnmnc-approved-mineral-symbols.pdf |date=2023-08-28 }})</ref> <ref name="Olds">{{cite journal |last1=Olds |first1=Travis A. |last2=Plášil |first2=Jakub |last3=Kampf |first3=Anthony R. |last4=Škoda |first4=Radek |last5=Burns |first5=Peter C. |last6=Čejka |first6=Jiří |last7=Bourgoin |first7=Vincent |last8=Boulliard |first8=Jean-Claude |title=Gauthierite, KPb[(UO<sub>2</sub>)<sub>7</sub>O<sub>5</sub>(OH)<sub>7</sub>]·8H<sub>2</sub>O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology |journal=European Journal of Mineralogy |date=2017 |volume=29 |issue=1 |pages=129–141 |doi=10.1127/ejm/2017/0029-2586 |bibcode=2017EJMin..29..129O |url=https://www.schweizerbart.de/papers/ejm/detail/29/87388/Gauthierite_KPb%5BUO27_O5_OH7%5D_8H2_O_a_new_uranyl_oxide_hydroxy_hydrate_mineral_from_Shinkolobwe_with_a_novel_uranyl_anion_sheet_topology |access-date=2023-07-13 |archive-date=2023-08-28 |archive-url=https://web.archive.org/web/20230828232926/https://www.schweizerbart.de/papers/ejm/detail/29/87388/Gauthierite_KPb%5BUO27_O5_OH7%5D_8H2_O_a_new_uranyl_oxide_hydroxy_hydrate_mineral_from_Shinkolobwe_with_a_novel_uranyl_anion_sheet_topology |url-status=live |url-access=subscription }}</ref>
</references>
== External links == * {{Commonscat inline|Gauthierite}} * [https://www.handbookofmineralogy.org/pdfs/gauthierite.pdf Gauthierite] in the ''Handbook of Mineralogy'', Mineralogical Society of America
Category:Geology of the Democratic Republic of the Congo Category:Lead minerals Category:Uranium(VI) minerals Category:Oxide minerals Category:Hydroxide minerals Category:Potassium minerals Category:Octahydrate minerals Category:Radioactive minerals Category:Monoclinic minerals Category:Minerals described in 2017