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 describe d. Aggregates and single crystals up to 0.5 x 0.3 x 0.03 mm3 in size o ccur on anglesite and in association with devillite-serpierite in vugs of a silver-rich galena ore which was found near and probably affecte d by an ancient silver smelter in Lautenthal, Harz Mountains, Germany. The mineral name refers to this locality. Type material is kept at th e Mineralogisches Institut, Ruhr-Universitat, Bochum, Germany. The min eral is transparent blue, non-fluorescent with a white streak and a vi treous lustre. It shows two good cleavages parallel to (001) and (010) . The crystals are platy after {100}, and bounded by {010}, {101}, {10 2}, {110}, and {514BAR} crystal faces. Twins after (100), frequently p olysynthetic, are common. Lautenthalite is biaxial negative with (lamb da = 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 sho ws 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 m ineral 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 res idue of PbSO4. X-ray film and structure analyses with an automated 4-c ircle 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 powd er 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) (421,71 1), 2.421(30) (518BAR,811BAR), 2.212(40) (019,019BAR,526BAR), 1.959(30 ) (426,132,820,231).