Guilleminite
(repeating unit)Ba(UO2)3(SeO3)2(OH)4·3H2O IMA symbol Gul[1] Strunz classification 4.JJ.10 Dana classification 34.07.03.01 Crystal system Orthorhombic Crystal class Pyramidal (mm2)
(same H-M symbol) Space group P21nm Unit cell 869.48 Å3 Identification Color Bright yellow, greenish yellow, yellow Cleavage Perfect on {100}, good on {010} Fracture Brittle Tenacity Brittle Mohs scale hardness 2 Luster Waxy, greasy, dull, earthy Diaphaneity Transculent Specific gravity 4.88 Optical properties Biaxial (−) Refractive index nα = 1.720 nβ = 1.798 nγ = 1.805 Birefringence 0.085 Pleochroism Strong 2V angle Measured 35°, calculated 32° Dispersion r > v strong Other characteristics 
RadioactiveReferences [2][3][4]
(same H-M symbol)
RadioactiveGuilleminite (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.[3]
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.[5]
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
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Mineralienatlas
- ^ a b Guilleminite: Guilleminite mineral information and data on Mindat.org
- ^ Webmineral data
- ^ Pierrot R, Toussaint J, Verbeek T. Bull. Soc. Franc. Mineral. Crist. 1965; 88: 132.
