Francevillite is a uranyl-group vanadate mineral in the tyuyamunite series. Its chemical formula is (Ba, Pb)(UO2)2V2O8·5(H2O). It is an orthorhombic-dipyramidal mineral containing barium, hydrogen, lead, oxygen, uranium, and vanadium. Francevillite is a strongly radioactive mineral. It is typically orange, yellow or brownish yellow. It forms a series with curienite.
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 after the city.
- Category: Vanadate mineral
- Formula: (Ba, Pb)(UO2)2V2O85(H2O)
- Crystal system: Orthorhombic
- Crystal class: Dipyramidal (mmm)
- Color: Lemon-yellow, yellow-orange, orange, greenish yellow; green, brown
- Crystal habit: Aggregates and incrustations of crystals, also massive, in veinlets and as impregnations
- Mohs scale hardness: 3
- Luster: Adamantine – pearly
- Streak: Light yellow
- Diaphaneity: Semitransparent
- Specific gravity: 4.55
- Optical properties: Biaxial (-)
Francevillite occurs in the oxidized zone of lead-bearing uranium-vanadium deposits. At its type locality, it is associated with curienite (a closely related uranyl vanadate), chevetite (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.