Metastudtite, UO 4 . 2H 2 O, a new mineral from Shinkolobwe, Shaba, Zaire

Metastudtite occurs at the Shinkolobwe uranium deposit in Shaba, Zaire. It appears as aggregates of flexible pale yellow fibers. Electron microprobe analysis gave UO₄ 88.1%. H₂O by TGA∼ 10%. Formula UO₄ · 2H₂O. Powder data are similar to those of the synthetic compound and to those of heated studtite (UO₄ · 4H₂O). Orthorhombic, probable space group Immm, a = 6.51(1), b = 8.78(2), c = 4.21(1)Å, Z = 2, d(calc.) = 4.67 mg/cm³. Strongest lines in the X-ray powder pattern are 5.22 (100)(110), 3.54 (80) (101), 4.38 (50)(020) and 3.79 (50)(011). The mineral is optically biaxial positive, γ = 1.760 (parallel to c, fiber axis), β = 1.658 and α = 1.640. Metastudtite is associated with uranophane, kasolite and hydrated uranium-lead oxides. Metastudtite is compared with studtite and lepersonnite.