IZOKLAKEITE FROM VENA, SWEDEN, AND THE KOBELLITE HOMOLOGOUS SERIES

Izoklakeite from Vena, Swede:r occurs in aggregates up to a few mm in diameter, intergrown with jask6lskiite, native bismuth, galena, pyrrhotite and, rarely, native antimony. The average of 19 electron-microprobe analyses is Pb 50.01, Bi 19.20, Sb 11.67, Cu 0.88, Ag 0.59, Fe 0.19, S 16.91. sum 99,45 wtVo. Based on 96 cations and ll4 S the analytical formula of izoklakeite from Vena is Pb5t.2esb20.37Bi1e.52Cu2.e4Ag1.16Fe6.72S1 14 or, ideally,(Cu,Fe)2Pb25.5(Sb,Bi)1e.5S57. The unit cell Ls orthorhom-bjc, with a tL.u(l), b 37.98(l), c 4.072(l) A, v: 5269.1 A3, space group Pnnm, Z = 2. Structurally any crystal in the kobellite homologous series (the Pb-Bi-Sb-Cu-Fe-Ag sulfosalts) conpists pf two types of rods, which are inter-nested in a pseudotrigonal pattern. The rods alternate in both a and b directions. The larger type of rod is based on a PbS-like archetype and has general ^ formula Mq1ya1;S7p.19i the smaller type represents a 2A-sheared PbS structure, with general formula MapSa11,*,;. Two strings oftetrahedrally co-ordinated (Cu,Fe) atoms for each pair of rods are added at the interfaces of the rods. Th1: complete formula is 2(Cu,Fe)2M10N+6SllN+13 for a ut-A repeat subunit of the structure. The order N of the homo-logue expresses the width of the smaller rods as a number of (Sb,Bi) co-ordination pyramids with common vertical edges, strung across the rod. Natural phases of the kobel-lite homologous series include kobellite and tintinaite with N:2, and giessenite and izoklakeite with N = 4