{{Short description|Rare uranium/selenium mineral}} {{Infobox mineral | name = Guilleminite | boxbgcolor =#6dd166 | image = Guilleminite-Vandenbrandeite-Cuprosklodowskite-201031.jpg | imagesize = 260px | caption = A cuprosklodowskite vug filled with well formed dark green vandenbrandeite crystals. These are dusted over with small yellow crystals of guilleminite. | category = Oxide minerals | formula = Ba(UO<sub>2</sub>)<sub>3</sub>(SeO<sub>3</sub>)<sub>2</sub>(OH)<sub>4</sub>·3H<sub>2</sub>O | IMAsymbol = Gul<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | strunz = 4.JJ.10 | system = Orthorhombic |dana=34.07.03.01| class = Pyramidal (mm2) <br/><small>(same H-M symbol)</small> | symmetry = ''P2''<sub>1</sub>nm | unit cell =869.48 Å<sup>3</sup> | color =Bright yellow, greenish yellow, yellow | cleavage =Perfect on {100}, good on {010} | fracture =Brittle | tenacity =Brittle | mohs =2 | luster =Waxy, greasy, dull, earthy | diaphaneity =Transculent | gravity =4.88 | opticalprop =Biaxial (−) | refractive =nα = 1.720 nβ = 1.798 nγ = 1.805 | birefringence =0.085 | pleochroism =Strong | 2V =Measured 35°, calculated 32° | dispersion =r > v strong | other = 25px Radioactive | references = <ref name=atlas>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Guilleminite Mineralienatlas]</ref><ref name=Mindat/><ref name=Webmin>[http://webmineral.com/data/Guilleminite.shtml Webmineral data]</ref> }} '''Guilleminite''' (Ba(UO<sub>2</sub>)<sub>3</sub>(SeO<sub>3</sub>)<sub>2</sub>(OH)<sub>4</sub>·3H<sub>2</sub>O) is a uranium mineral named by R. Pierrot, J. Toussaint, and T. Verbeek in 1965 in honor of Jean Claude Guillemin (1923–1994), a chemist and mineralogist. It is a rare uranium/selenium mineral found at the Musonoi Mine in the Katanga Province of the Democratic Republic of the Congo.<ref name=Mindat>[http://www.mindat.org/min-1771.html Guilleminite: Guilleminite mineral information and data on Mindat.org]</ref>
This secondary mineral also includes barium in its structure, in addition to selenium and uranium. It is bright yellow in colour and usually has an acicular crystal habit. It has a Mohs hardness of 2–3.<ref>[http://rruff.info/uploads/BSFMC88_132.pdf Pierrot R, Toussaint J, Verbeek T. ''Bull. Soc. Franc. Mineral. Crist.'' 1965; 88: 132.]</ref>
== Pleochroism == Guilleminite shows strong pleochroic attributes. Depending on the axis the gem is seen, guilleminite on the X axis can be seen in a bright yellow color, on the Y axis can be seen yellow, and on the Z axis is seen as a colorless gem.
==References== {{reflist}}
Category:Barium minerals Category:Uranium(VI) minerals Category:Selenite minerals Category:Orthorhombic minerals Category:Minerals in space group 31 Category:Trihydrate minerals Category:Minerals described in 1965