Francevillite Yellow crystals of francevillite on matrix with small mounanaite crystals (specimen size, 4 x 3.5 x 1 cm)
Category Vanadate mineral Formula (repeating unit) (Ba,Pb)(UO2 )2 V2 O8 ·5(H2 O) IMA symbol Fvl[ 1] 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 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 [ 2] [ 3] [ 4] [ 5]
Francevillite is a uranyl-group vanadate mineral in the tyuyamunite series. Its chemical formula is (Ba,Pb)(UO2 )2 V2 O8 ·5(H2 O) . 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] 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.
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
