Curienite and Francevillite are closely related, highly radioactive uranyl vanadate minerals that form a solid solution series. At the famous Oklo Mine in Gabon—the site of Earth's only known natural nuclear fission reactor—these secondary minerals formed in the heavily oxidized zones surrounding the ancient, two-billion-year-old uranium ore bodies.
The Curienite-Francevillite Series
These two minerals share an identical structural framework, consisting of uranyl vanadate layers. The core difference lies in the specific element trapped between those layers to balance the chemical charge:
MineralChemical FormulaDominant Interlayer CationAppearance at Oklo
CurienitePb(UO₂)₂(VO₄)₂ ⋅ 5H₂OLead (Pb²⁺)Bright yellow to orange crystals
Francevillite(Ba,Pb)(UO₂)₂V₂O₈ ⋅ 5(H₂O)Barium (Ba²⁺)Yellow, orange, or brownish-yellow
Because they form a solid solution series, pure endmembers are rare. A single mineral specimen from the Mindat Oklo Mine Entry typically contains a mixture of both lead and barium. If the mineral structure contains more than 50% lead, it is classified as curienite; if barium is dominant, it is classified as francevillite.
Significance at the Oklo Natural Reactor
The presence of curienite and francevillite at the Oklo Mine provides crucial geochemical insights:
• Oxidation Markers: Both minerals are secondary weathering products. They formed long after the nuclear reactors shut down, occurring when groundwater interacted with the primary uraninite ore in the presence of vanadium and lead.
• Lead Retention Studies: The lead (Pb) found in the curienite structure is largely radiogenic—meaning it is the stable decay product of the original uranium. Scientists study these minerals to understand how successfully natural geological environments can trap and lock away radioactive decay products over billions of years.
• Type Locality Proximity: Both minerals were officially first described from the nearby Mounana uranium mine (the type locality for both species)
This is a great size with nice orange coverage and come with the vintage Eric Quinter label. Rare and with top notch provenance.
7.5x5.1x4.1 cm
156 grams
Over 300,000 cpm on Radiacode 110
Mounana, Gabon, Africa (TL)
Inside Back Shelf
