| Guilleminite | |
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| Category: | Oxide minerals |
| Formula: | Ba(UO2)3(SeO3)2(OH)4·3H2O |
| Imasymbol: | Gul[1] |
| 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, good on |
| 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: | Radioactive |
| References: | [2] [3] |
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.[4]
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]
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.