LAHNSTEINITE, Zn <sub>4</sub>(SO <sub>4</sub>)(OH) <sub>6</sub> · 3H <sub>2</sub>O, A NEW MINERAL FROM THE FRIEDRICHSSEGEN MINE, GERMANY
A new mineral lahnsteinite has been found on the wast dump of Friedrichssegen mine, in Lahn valley, Bad Ems district, Rhineland-Palatinate (Rheinland-Pfalz), Germany. It occurs in the supergene association including goethite, hydrozincite, pyromorphite and native copper. Colourless tabular crystals of lahnsteinite, up to 0.15 X 0.5 X 0.5 mm in size, occur in cavities in massive goethite. The mineral is sectile, with Mohs' hardness of 1.5 and perfect, mica-like cleavage on (100). D calc = 2.995, D meas = 2.98(2) g/cm 3. IR spectrum is given. Lahnsteinite is optically biaxial (-), α = 1.568(2), β = 1.612(2), γ = 1.613(2), 2V meas = 18(3)°, 2V calc = 17°. Chemical composition (electron microprobe, H 2O by gas chromatography of ignition products at 1200 °C, wt %) is: FeO 3.87, CuO 1.68, ZnO 57.85, SO 3 15.83, H 2O 22.3, total 101.53. The empirical formula is: (Zn 3.53Fe 0.27Cu 0.11) Σ3.91(S 0.98O 4) (OH) 6 · 3H 2.10O. The crystal structure was refined on single crystal. Lahnsteinite is triclinic, P1; space group P1 unit-cell parameters are: a = 8.3125(6), b = 14.545(1), c = 18.504(2) Å, α = 89.71(1)°, β = 90.05(1)°, γ = 90.13(1)°, V = 2237.2(3) Å 3, Z = 8. The strongest lines of the X-ray powder diffraction pattern [d, Å (I, %)] are: 9.30 (100), 4.175 (18), 3.476 (19), 3.290 (19), 2.723 (57), 2.624 (36), 2.503 (35), 1.574 (23). The mineral was named after the discovery locality near the city of Lahnstein. The type specimen is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, with registration number 4252/1.