Asselbornite, (Pb,Ba)(UO₂)₆(BiO)₄[(As,P)O₄]₂(OH)₁₂ · 3H₂O, occurs with metauranospinite, uranophane and uranosphaerite at Schneeberg, Saxony, Eastern Germany. The name is in honour of Eric Asselborn. Electron microprobe analyses have shown a fairly uniform distribution of elements and the absence of other minor components. X-ray powder diffraction data were obtained using Gandolfi and Guinier-Hägg cameras. The single crystal study has been performed with a Weissenberg camera. The crystal system is cubic with a cell parameter a = 15.66 Å. The probable space groups are Im3m, I432, Im3 or I23. With Z = 4, the calculated specific gravity is 5.6g/cm³ using the empirical formulas. Prominent X-ray diffraction lines occur at the following spacings in Å: 6.39(30)(211), 5.536(40)(220), 4.520(70)(222), 4.185(100)(321), 3.691(60)(330), 3.501(35)(420), 3.196(80)(422), 2.609(40)(600)(442), 1.988(25)(651)(732). The mineral, brown to lemon yellow in colour, is transparent with a greasy to adamantine lustre. Well crystallized asselbornite appears as cubes, more or less troncated cubes or as a combination of both with a maximum size of 0.3 mm. Optically isotropic with n ≈ 1 .9, it is yellow in thin section.