LAUTENTHALITE, PBCU4[(OH)6](SO4)2].3H2O THE PB ANALOG OF DEVILLITE - A NEW MINERAL FROM THE HARZ MOUNTAINS, GERMANY

The new mineral lautenthalite, a Pb analogue of devillite, is described. Aggregates and single crystals up to 0.5 x 0.3 x 0.03 mm3 in size occur on anglesite and in association with devillite-serpierite in vugs of a silver-rich galena ore which was found near and probably affected by an ancient silver smelter in Lautenthal, Harz Mountains, Germany. The mineral name refers to this locality. Type material is kept at the Mineralogisches Institut, Ruhr-Universitat, Bochum, Germany. The mineral is transparent blue, non-fluorescent with a white streak and a vitreous lustre. It shows two good cleavages parallel to (001) and (010). The crystals are platy after {100}, and bounded by {010}, {101}, {102}, {110}, and {514BAR} crystal faces. Twins after (100), frequently polysynthetic, are common. Lautenthalite is biaxial negative with (lambda = 589 nm): n(x) = 1.659(2), n(y) AND C = 4(1)-degrees = 1.703(2), n(z) parallel-to b = 1.732(2), 2V(meas) = 79(1)-degrees, r > v, and shows a faint pleochroism with X = pale blue, Y and Z = blue. Microprobe analyses of three different crystals revealed (wt %): PbO = 27.2, CuO = 39.3, SO3 = 19.7, H2O (by difference) = 13.7, corresponding to the mineral formula Pb0.99Cu4.01S2O8(OH)6 . 3.1H2O, or ideally PbCu4[(OH)6\(SO4)2] . 3H2O. Lautenthalite reacts with cold HCl to form a white residue of PbSO4. X-ray film and structure analyses with an automated 4-circle diffractometer (R = 5.9%) proved the isotypy with devillite, s.g. = P2(1)/c, and a = 21.642(8), b = 6.040(2), c = 22.544(8) angstrom, beta = 108.2(1)-degrees, V = 2799 angstrom3, Z = 8. The strongest powder lines are: 10.2(20) (200), 5.14(100) (400), 4.53(60) (310), 3.40(80) (510), 2.821(30) (317BAR), 2.631(50) (024,024BAR), 2.531(40) (421,711), 2.421(30) (518BAR,811BAR), 2.212(40) (019,019BAR,526BAR), 1.959(30) (426,132,820,231).