Dark brown crystal group of the rare uranium mineral calciouranoite from the type locality in Russia: Oktyabr'skoe Deposit, Krasnokamensk, Chitinskaya Oblast, Zabaykalsky Krai, Russian Federation. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Calciouranoite
Calciouranoite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Ca,Ba,Pb,K,Na)U₂O₇·5H₂O.
It is a member of the Wölsendorfite structural group.
Key properties: Mohs hardness 4; specific gravity 4.62; Greasy to dull luster; optically biaxial.
IMA symbol Cun, IMA status: approved, named in 1973.
Found in stringers in felsite, deep in the oxidation zone of a U–Mo deposit, in water-saturated ore-bearing faults.
It is found associated with Calcite, uranophane, bauranoite, metacalciouranoite, protasite.
The name refers to CALCIum and URANium in the composition.