The roubaultite Cu2(UO2)3(OH)10.5H2O, a new mineral species

Roubaultite Cu₂ (UO₂)₃ (OH)₁₀ • 5 H₂O originates from the oxidation zone of the Shinkolobwe uranium deposit in Katanga, where it is associated with becquerellite, vandenbrandite, soddyite, and cuprosklodowskite. The symmetry is triclinic P1 or P[-1] with a = 7.73 Å, b = 6.87 Å, c = 10.87 Å, α = 86°29', β = 134°12', γ = 93°10' and Z = 1. The main lines of the powder diffraction pattern are: 7.74 (9) [-1]01; 6.88 (8) 010; 5.55 (10) 100; 3.448 (8) 10[-3]-[-2]12; 3.326 (8) [-1]21; 3.175 (8) [-2]11. Roubaultite is biaxial positive with n'p = 1.700; n'm = 1.800; n'g = 1.83. The study of the dispersion of reflective powers leads to indices equal to 1.843 and 1.782 for λ = 580 nm. There is perfect cleavage {100} and good cleavage {010}; the calculated density is equal to 5.02 g/cm³. The chemical analysis gives: CuO = 13.5%, SeO₂ = 0.3%, UO₃ = 71.6%, H₂O = 14.8%, total = 100.2%. This mineral is named in honor of Professor Marcel Roubault and is preserved in the collection of the École nationale supérieure des Mines de Paris.