Guilleminite , Malachite Locality: Musonoi Mine, Kolwezi , Western area, Katanga Copper Crescent, Katanga (Shaba) , Democratic Republic of Congo (Zaïre) ( Locality at mindat.org ) Size: 4.3 x 4.2 x 3.2 cm. An exceptionally rich specimen featuring lemon-yellow, sub-mm crystals of the rare species Guilleminite on malachite. TYPE LOCALITY. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Guilleminite
A yellow barium uranyl selenite named in 1965 for chemist Jean-Claude Guillemin.
Intro adapted from Wikipedia (CC BY-SA).
Guilleminite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Ba(UO₂)₃(Se⁴⁺O₃)₂O₂·3H₂O.
It crystallizes in the orthorhombic crystal system (space group P2_1nm).
Key properties: specific gravity 4.88; [Vitreous.] luster; optically biaxial.
IMA symbol Gul, IMA status: approved, named in 1964.
Found in the oxidized portions of a Cu–Co sulfide deposit (Musonoi mine, Congo).
It is found associated with Malachite, cuprosklodowskite, kasolite, marthozite, derriksite, uranophane, wulfenite (Musonoi mine, Congo).
The mineral was named to honor Dr. Claude Guillemin (1923–1994), eminent French mineralogist, Bureau de Recherches Géologiques et Minières, Paris, France.