Heisenbergite, a new uranium mineral from the uranium deposit of Menzenschwand in the Southern Black Forest, Germany

摘要

Heisenbergite is the seventh new uranium mineral first described from the uranium deposit of Menzenschwand in the Southern Black Forest, Baden Wurttemberg, Germany. It occurs there as a rare secondary mineral associated with quartz, baryte, uraninite, billietite, studtite, rutherfordine, joliotite, goethite and hematite. Its occurrence is not restricted to Menzenschwand, but it was also found at El Sherana, South-Alligator-River-District in the Northern Territory of Australia from where it was described as an unnamed uranium oxide by Threadgold (1960). A further occurrence is Joachimsthal in the Czech Republic reported by Ondrus et al. (1997). The mineral and its name were approved by the CNMNC in January 2011 (IMA No. 2010-076). At Menzenschwand it forms, besides anhedral particles, long prismatic crystals up to about 15 ìm in length but only a few ìrn in thickness. The colour varies somewhat: yellow, yellow brown or orange brown. The streak is yellow, the lustre vitreous. Further properties are: opaque to translucent, particles in liquids transparent, not fluorescent, cleavage and parting not observed, fracture irregular. Hardness (Mohs) about 2, density (calc.) 5.14g/cm~3. Refractive indices: n_á 1.733(3), n_? 1.800(5), n_? close to n_?, optical character (-). Extinction straight with 1 (= Z) positive. As no single crystal studies were possible due to the small size of the crystals, the dimensions of an orthorhombic unit cell were derived from the indexed powder data: a 13.10(1) A, b 13.76(1), c 14.50(1), V 2613,7(2) A~3, Z = 24. Posssible space groups: P2_12_12_1, Pna2_1, Pnma. Strongest lines of the powder pattern: 7.92 A (10) 111; 7.25 (9) 002; 3.57(7) 321; 3.27 (9) 322, 400. Chemical composition determined by electron microprobe (wt.%): UO_3 88.58, PbO 1.31, BaO 0.17, CaO 0.13, H_2O (by difference) 9.81, total 100.00%, being similar to the composition of schoepite UO_3 2.25H_2O, metaschoepite UO_3 2H_2O, and paulscherrerite UO_2(OH)_2. The empirical formula based on 5 oxygen atoms is U_(1.044)Pb_(0.020)Ba_(0.004) Ca_(0.008)H_(3.672)O_5, simplified UO_2(OH)_2 H_2O, or UO_3 2H_2O. The mineral is easily soluble in HC1 1:1 and HN03 1:1. On the basis of Raman spectral data it is suggested that two distinct type of coordination polyhedra for uranium are present in the heisenbergite structure.