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Bayldonite, (Cu,Zn)3Pb(AsOa)2(OH)2 from Tsumeb, S.W. Africa, is monoclinic, space group C2/c, with cell dimensions: a = 10.147(2), b = 5.892(1), c = 14.081 (2) A, fl = 106.05 (1) ° and Z = 4. The crystal structure has been determined by the heavy-atom method and refined by the full-matrix least-squares method to an R factor of 0.053 for 1057 observed Xray reflections. The crystal structure of bayldonite consists of interconnected Cu octahedral layers and lead arsenate polyhedral-tetrahedral layers which alternate along the c axis, giving rise to complex pseudohexagonal layers parallel to (001). The Cu octahedral sheet, with six-membered octahedral tings, is formed by three crystallographically indep_endent [CuO4(On)2] octahedra with point symmetry 1, showing Jahn-Teller distortion; the square-planar Cu-O (or OH) distances vary from 1.878 to 2.087 A (average 1.970 A), whereas the apical Cu-O distances vary from 2.272 to 2.474 A. The PbO s polyhedron is a square antiprism with an average Pb--O bond length of 2.722/k. The tetrahedral As-O bond lengths vary from 1.66 to 1.724 A (average 1-696 A). The H atom appears to be disordered between the (OH) group and a highly charge-deficient O atom, which is bonded to one Pb atom, in addition to the As atom. The observed twinning, cleavage and crystal habit result from the pseudohexagonal nature of the layer structure.

Bellingerite, 3Cu(IO3)2.2HzO, is triclinic, space group P1, with a0 = 7.256 (2), b0 = 7.950 (2), co = 7.856 (2) A, ~=105-10 (2), /3=92.95 (2), and y=96.95 (2) °, Z= 1. The heavy-atom positions were determined from a three-dimensional Patterson map. The crystal structure was determined by the heavy-atom method and refined by the method of least-squares, with anisotropic temperature factors, to an R of 0.038 for 3156 reflections measured on an automatic single-crystal diffractometer. The standard error in Cu-O and I-O bond lengths is + 0.005 A and in O-Cu-O and O-I-O angles + 0.02 °. The crystal structure of bellingerite is a three-dimensional framework consisting of a corner-sharing tetragonally distorted Cu(l)O6 octahedron, a [Cu(2)2Os(H20)2] octahedral dimer and three independent pyramidal iodate groups. Cu(1) at a symmetry center is bonded to four oxygens at 1.936 A ( × 2) and 1.967 A ( × 2) approximately in a square plane, while two oxygens at 2.528A ( × 2) complete the octahedron. Cu(2) has three oxygen atoms at 1.942, 1.946 and 1.973 A and a water molecule at 1.950 A approximately in a square plane, while one oxygen at 2-456 A and a water molecule at 2.483 A form the apices of the distorted octahedron. Two Cu(2) octahedra form a dimer by sharing an octahedral edge. The pyramidal I(1)O3 group, with point-group symmetry 3m, has three oxygens at 1-815, 1.823 and 1.824 A from the iodine atom, with O-I-O angles 96.0, 95.7 and 97-3 °.

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