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| Francevillite | |
| Category: | Vanadate mineral |
| Imasymbol: | Fvl[1] |
| Strunz: | 4.HB.15 |
| Dana: | 40.02a.27.01 |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Pcan |
| Unit Cell: | a = 10.41, b = 8.51 c = 16.76 [Å]; Z = 4 |
| Color: | Lemon-yellow, yellow-orange, orange, greenish yellow; green, brown |
| Habit: | Aggregates and incrustations of crystals, also massive, in veinlets and as impregnations |
| Cleavage: | On, perfect |
| Mohs: | 3 |
| Luster: | Adamantine - pearly |
| Streak: | Light yellow |
| Diaphaneity: | Semitransparent |
| Gravity: | 4.55 |
| Opticalprop: | Biaxial (-) |
| Refractive: | nα = 1.750 - 1.785 nβ = 1.910 - 1.952 nγ = 1.945 - 2.002 |
| Birefringence: | δ = 0.195 - 0.217 |
| Pleochroism: | X = colorless; Y = Z = yellow |
| 2V: | Measured: 52°, Calculated: 46° to 52° |
| Other: | Radioactive |
| References: | [2] [3] [4] [5] |
Francevillite is a uranyl-group vanadate mineral in the tyuyamunite series. Its chemical formula is . Francevillite is a strongly radioactive mineral. It is typically orange, yellow or brownish yellow. It forms a series with curienite.[2]
Francevillite occurs in the oxidized zone of a lead-bearing uranium–vanadium deposits.[2] Francevillite was first described in 1957 for an occurrence in its type locality of the idle Mounana uranium mine, near Franceville, Haut-Ogooué, Gabon and was named for the city.[3] [4]
At its type locality it is associated with curienite (a closely related uranyl vanadate), chervetite (a lead vanadate), and mounanaite (another lead vanadate). At other localities, francevillite is associated with duttonite, vanuralite, mottramite, carnotite, dewindtite, torbernite, uranopilite, johannite and kasolite.[2]