Vote for your favorite mineral in #MinCup26! - Sphalerite vs. Anorthite Both zinc ore Sphalerite and calcium plagioclase feldspar Anorthite have perfect cleavage that will split cleanly if you hit them with a hammer, but only one can claim a larger split of your votes!
Hatert et al. (2000): "Associated with altered galena and with pyromorphite, wulfenite occurs as isolated crystals up to 2 mm. They are orange-coloured, with a greasy luster. Crystals generally form very acute tetragonal dipyramids with curved faces unsuitable for goniometric measurements. Wulfenite crystallizes also as {101} tetragonal dipyramids, of which the orientation has been checked by X-ray diffraction. These crystals are sometimes modified by the forms {001} and {1k0}, with a relatively high k value difficult to determine with the classical goniometric methods. Both prismatic and tabular crystals exist. Some tabular crystals give the combination {100} {001}, sometimes modified by the small faces {101}. It is to be pointed out that tabular crystals of wulfenite, as well as crystals with {1k0} faces, had never been observed in Belgium so far. The parameters of the tetragonal unit-cell of wulfenite from Bastogne have been calculated from 26 reflections: a = 5.429(1) Å and c = 12.097(6) Å. These values correspond better with those given by Fransolet et al. (1977) for the wulfenite from Richelle than with those given by Hatert et al. (1998) for the wulfenite from Vielsalm. Chemical analysis shows Pb and Mo together with minor Fe and Cd. The presence of noticeable quantities of Fe and Cu into the lattice of the wulfenite from Vielsalm (Hatert et al 1998) could be responsible for the lower values of its unit-cell parameters when compared with these calculated for minerals from Bastogne and Richelle."
