Heisenbergite, a new uranium mineral from the uranium deposit of Menzenschwand in the Southern Black Forest, Germany
Walenta, Kurt; Theye, Thomas
published: Apr 1, 2012
ArtNo. ESP154018902001, Price: 29.00 €
Heisenbergite is the seventh new uranium mineral first described from the uranium deposit of Menzenschwand in the Southern Black Forest, Baden Württemberg, 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 ondruš 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 μm in length but only a few μm 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.) 5.14 g/cm3. Refractive indices: nα 1.733(3), nγ 1.800(5), nβ close to nγ, optical character (-). Extinction straight with l (= 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) Å, b 13.76(1), c 14.50(1), V 2613,7(2) Å3, Z = 24. Posssible space groups: P212121, Pna21, Pnma. Strongest lines of the powder pattern: 7.92 Å (10) 111; 7.25 (9) 002; 3.57(7) 321; 3.27 (9) 322, 400. Chemical composition determined by electron microprobe (wt.%): UO3 88.58, PbO 1.31, BaO 0.17, CaO 0.13, H2O (by difference) 9.81, total 100.00 %, being similar to the composition of schoepite UO3 · 2.25H2O, metaschoepite UO3 · 2H2O, and paulscherrerite UO2(OH)2. The empirical formula based on 5 oxygen atoms is U1.044Pb0.020Ba0.004Ca0.008H3.672O5, simplified UO2(OH)2 · H2O, or UO3 · 2H2 O. The mineral is easily soluble in HCl 1:1 and HNO3 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.