Francevillite
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 3.0)
Mineral NameFrancevillite
Chemical Formula(Ba,Pb)(UO2)2(VO4)2·5H2O
Mohs Hardness3
Crystal Systemorthorhombic
Streak Coloryellow
Cleavageperfect on {001}
Fractureuneven
Specific Gravity4.5
Colorsorange-yellow, brownish-orange, yellow, brown
Transparencytransparent to translucent
Type LocalityMounana Mine, Franceville, Haut-Ogooué, Gabon
Mineral GroupVanadates
Usescollector, scientific_interest
Associated MineralsMounanaite
Rarityuncommon
Description
This specimen features a dark matrix covered by numerous small, blocky to tabular crystals of Francevillite, displaying vibrant orange-yellow to brownish-orange hues, often forming crusts. Smaller, more yellowish granular crystals, possibly Mounanaite, are also present.
Geological Context
Francevillite is a secondary uranium mineral that forms in the oxidized zones of uranium-vanadium deposits, resulting from the alteration of primary uranium minerals in the presence of barium, lead, and vanadium. The Mounana Mine is its type locality and a significant uranium deposit.
