Francevillite is a uranyl-group vanadate

Vanadate

In chemistry, a vanadate is a compound containing an oxoanion of vanadium generally in its highest oxidation state of +5. The simplest vanadate ion is the tetrahedral, orthovanadate, VO43− anion, which is present in e.g. sodium orthovanadate and in solutions of V2O5 in strong base...

 mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 in the tyuyamunite series. Its chemical formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 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.

Occurrence

Francevillite occurs in the oxidized zone of a lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

-bearing uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

–vanadium

Vanadium

Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

 deposits. Francevillite was first described in 1957 for an occurrence in its type locality

Type locality (geology)

Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 of the idle Mounana uranium mine, near Franceville

Franceville

Franceville or Masuku is one of the four largest cities in Gabon, with a population of around 22,000 people. It lies on the River Mpassa and at the end of the Trans-Gabon Railway and the N3 road. It grew from a village named Masuku when Pierre Savorgnan de Brazza chose it to resettle former...

, Haut-Ogooué, Gabon

Gabon

Gabon , officially the Gabonese Republic is a state in west central Africa sharing borders with Equatorial Guinea to the northwest, Cameroon to the north, and with the Republic of the Congo curving around the east and south. The Gulf of Guinea, an arm of the Atlantic Ocean is to the west...

 and was named for the city.

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

Mottramite

Mottramite is an orthorhombic mineral, PbCu, at the copper end of the descloizite group. It was formerly called cuprodescloizite or psittacinite .-References:***...

, carnotite

Carnotite

Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K222·3H2O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present.-Occurrence:...

, dewindtite, torbernite

Torbernite

The chemical formula of torbenite is similar to that of autunite in which a Cu2+ cation replaces a Ca2+. The number of water hydration molecules can vary between 12 and 8, giving rise to the variety of metatorbernite when torbernite spontaneously dehydrates...

, uranopilite

Uranopilite

Uranopilite is a minor ore of uranium with the chemistry 6SO46O2·12H2O or, Hydrated Uranyl Sulfate Hydroxide.As with many uranyl minerals, it is fluorescent and radioactive. It is straw yellow in normal light. Uranopilite fluoresces a bright green under ultraviolet light...

, johannite

Johannite

Johannite is a rare uranium sulfate mineral. It crystallizes in the triclinic crystal system with the chemical composition Cu[UO2SO4]2·8H2O. It crystallizes in the triclinic system and develops only small prism or thin to thick tabular crystals, usually occurs as flaky or spheroidal aggregates and...

 and kasolite.