guilleminite

{{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(UO2)3(SeO3)2(OH)4·3H2O | IMAsymbol = Gul | strunz = 4.JJ.10 | system = Orthorhombic |dana=34.07.03.01| class = Pyramidal (mm2) (same H-M symbol) | symmetry = P21nm | unit cell =869.48 Å3 | 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 = }} Guilleminite (Ba(UO2)3(SeO3)2(OH)4·3H2O) 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.

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.