Abstract
The investigation of studtite from the uranium deposit of Menzenschwand in the Black Forest shows that thisill-defined species is not a uranyl carbonate as hitherto assumed but a hydrous uranium oxide of monoclinic symmetry. It is identical with a synthetic uranium compound which is regarded as peroxide hydrate UO4·4 H2O (Sato, 1961). If this interpretation is correct, studtite would be the first peroxide mineral found in nature. Unit-cell dimensions of the mineral from Menzenschwand are: a 11.85, b 6.80, c 4.25 Å β 93°51ߣ, Z = 2, space group C2, Cm, or C2/m, density (calc) 3.64 g/cc. Strongest lines of the powder pattern are 5.93 (10), 3.40 (8), 2.96 (6). The X-ray data agree closely with those given by Debets (1963) for the synthetic compound. The structure of studtite probably consists of O-U-O-U-O chains in the direction of the c-axis as in case of α-UO3.
When heated to 60°C, studtite is transformed into a dihydrate, UO4.2 H2O with loss of 2 H2O. This dihydrate, which is also known as a synthetic compound, is orthorhombic with a 6.51, b 8.78, c 4.21 Å, Z = 2, spacegroup probably Immm, density (calc) 4.67 g/cc.
Strongest lines of the powder pattern: 5.24 (10), 4.41 (7), 3.54 (8).
A brief description is also given of a presumably new siliciferous mineral occurring at Menzenschwand associated with studtite and uranophane.
