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 | (Ba,Pb)(UO2)2V2O8·5(H2O) |
| IMA symbol | Fvl |
| 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 | |
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 curienite.