Francevillite

(Ba,Pb)(UO2)2V2O8·5(H2O)IMA symbolFvl[1]Strunz classification4.HB.15Dana classification40.02a.27.01Crystal systemOrthorhombicCrystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)Space groupPcanUnit cella = 10.41, b = 8.51
c = 16.76 [Å]; Z = 4IdentificationColorLemon-yellow, yellow-orange, orange, greenish yellow; green, brownCrystal habitAggregates and incrustations of crystals, also massive, in veinlets and as impregnationsCleavageOn {001}, perfectMohs scale hardness3LusterAdamantine - pearlyStreakLight yellowDiaphaneitySemitransparentSpecific gravity4.55Optical propertiesBiaxial (-)Refractive indexnα = 1.750 - 1.785 nβ = 1.910 - 1.952 nγ = 1.945 - 2.002Birefringenceδ = 0.195 - 0.217PleochroismX = colorless; Y = Z = yellow2V angleMeasured: 52°, Calculated: 46° to 52°Other characteristics RadioactiveReferences[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 curienite.[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 curienite (a closely related uranyl vanadate), chervetite (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.[2]

  • Yellow curienite on bright orange francevillite, in a specimen from their mutual type locality, the Mounana uranium mine, near Franceville. Specimen size: 23x17cm.
    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 Curienite (yellow) and Chervetite, Mounana Mine, Franceville, Haut-Ogooué Province, Gabon. Overall size 8.7 x 6.1 x 2.1 cm.
    Francevillite (orange) with Curienite (yellow) and Chervetite, Mounana Mine, Franceville, Haut-Ogooué Province, Gabon. Overall size 8.7 x 6.1 x 2.1 cm.

References

  1. ^ 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.
  2. ^ a b c d Handbook of Mineralogy
  3. ^ a b Mindat.org
  4. ^ a b Webmineral data
  5. ^ Francevillite Archived 2009-11-02 at the Wayback Machine at Uranium and Thorium Minerals of the World
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