Francevillite
| Francevillite | |
|---|---|
 Yellow crystals of francevillite on matrix with small mounanaite crystals (specimen size, 4 x 3.5 x 1 cm) | |
| General | |
| Category | Vanadate mineral |
| Formula (repeating unit) | (Ba,Pb)(UO2)2V2O8·5(H2O) |
| IMA symbol | Fvl[1] |
| Strunz classification | 4.HB.15 |
| Dana classification | 40.02a.27.01 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pcan |
| Unit cell | a = 10.41, b = 8.51 c = 16.76 [Å]; Z = 4 |
| Identification | |
| Color | Lemon-yellow, yellow-orange, orange, greenish yellow; green, brown |
| Crystal habit | Aggregates and incrustations of crystals, also massive, in veinlets and as impregnations |
| Cleavage | On {001}, perfect |
| Mohs scale hardness | 3 |
| Luster | Adamantine - pearly |
| Streak | Light yellow |
| Diaphaneity | Semitransparent |
| Specific gravity | 4.55 |
| Optical properties | Biaxial (-) |
| Refractive index | 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 angle | Measured: 52°, Calculated: 46° to 52° |
| Other characteristics |  Radioactive |
| References | [2][3][4][5] |
Francevillite is a uranyl-group vanadate mineral in the tyuyamunite series. Its chemical formula is (Ba,Pb)(UO2)2V2O8·5(H2O). Francevillite is a strongly radioactive mineral. It is typically orange, yellow or brownish yellow. It forms a series with .[2]
Occurrence[]
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 (a closely related uranyl vanadate), (a lead vanadate), and (another lead vanadate). At other localities, francevillite is associated with , vanuralite, mottramite, carnotite, , torbernite, uranopilite, johannite and .[2]
Yellow curienite on bright orange francevillite, in a specimen from their mutual type locality, the Mounana uranium mine, near Franceville. Specimen size: 23x17cm.
Francevillite (orange) with (yellow) and , Mounana Mine, Franceville, Haut-Ogooué Province, Gabon. Overall size 8.7 x 6.1 x 2.1 cm.
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.
- ^ a b c d Handbook of Mineralogy
- ^ a b Mindat.org
- ^ a b Webmineral data
- ^ Francevillite at Uranium and Thorium Minerals of the World
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- Uranium(VI) minerals
- Vanadate minerals
- Orthorhombic minerals
- Minerals in space group 60