Seleniferous lead–bismuth sulphosalts from Falun, Sweden; weibullite, wittite, and nordströemite

Studies of specimens from Falun, Sweden, reported to contain the two minerals weibullite and wittite have established at least three selenium-rich bismuth–lead sulphosalts of similar chemistry. A nomenclature is proposed in which two of the minerals retain the old names weibullite and wittite, while the third is given the new name nordströmite. Weibullite, Ag_0.32Pb_5.09Bi_8.55Se_6.08S_11.92, is orthorhombic Pnma with a = 53.68, b = 4.11, c = 15.40Å; nordströmite, CuPb₃Bi₇(Se₄,S₁₀), is monoclinic P2₁/m with a = 17.97, b = 4.11, c = 17.62Å and β = 94.30°. Wittite, Pb_0.3541Bi_0.4366(Se_0.2026,S_0.7974), is monoclinic with two lattices. The sub-cells of these two lattices are: lattice A, P2/m, a = 4.19, b = 4.08, c; = 15.56Å, β = 101.35°; lattice B, C2/m, a = 7.21, b = 4.08, c = 15.50Å, β = 98.75°. They are virtually identical to those found in cannizzarite.