Niedermayrite, Cu4Cd(SO4)2(OH)6 � 4H2O, a new mineral from the Lavrion Mining District, Greece

Abstract

Niedermayrite, Cu4Cd(SO4)2(OH)6 · 4H2O, is a new mineral discovered in 1995 in the Km3-area of the Lavrion mining district, Greece. It forms tiny euhedral plates, commonly intergrown as green crusts up to several cm2 in size on a matrix consisting of a brecciated marble with sphalerite, chalcopyrite, galena, greenockite, hawleyite and pyrite. Associated secondary minerals are gypsum, malachite, chalcanthite, brochantite, hemimorphite, hydrozincite, aurichalcite, one unknown Cd-sulfate, monteponite and otavite. Niedermayrite is non-fluorescent and has a bluish-green colour with vitreous lustre, the streak is white. The crystals are brittle with perfect cleavage parallel {010}. Optics: biaxial (−) with nα(calc.), nβ, and nγ =1.609, 1.642(2), and 1.661(2), respectively; orientation nα//b. The calculated density is 3.292 gcm−3. The most prominent form is {010}. Analysis by electron microprobe gives CdO 16.5, CuO 45.7, SO3 21.6, H2O 16.2 wt.% (calc. to 100% sum) and the empirical formula Cu4.29Cd0.96S2.01O11.28 · 6.71 H2O (based on 18 oxygens p.f.u.). By TGA an H2O content of 18.9 wt.% was obtained. The ideal formula (confirmed by the crystal structure refinement) is Cu4Cd(SO4)2(OH)6 · 4H2O with a theoretical H2O content of 17.2 wt.%. The strongest lines in the X-ray powder diffraction pattern (Gandolfi camera, visually estimated I, refined lattice parameters a = 5.535(2), b = 21.947(9), c = 6.085(2) A,β = 91.98(3)°) are: (dobs[A]/Iobs/hkl) (11.02/90/0 2 0), (5.874/20/0 1 1), (5.496/100/0 4 0), (5.322/25/0 2 1), (4.079/50/0 4 1), (3.660/20/0 6 0), (3. 437/30/1 5 0), (3.243/40/1 4 1), (2.470/30/2 4 0), (2.425/20/1 4 −2), (2.205/20/2 6 0) and (1.897/20/1 8 2). The mineral is monoclinic, P21/m, Z = 2, a = 5.543(1) A, b = 21.995(4) A, c = 6.079(1) A,β = 92.04(3)°, V = 740.7(2) A3. The crystal structure was determined by single crystal X-ray methods and was refined to R1= 0.026, wR2 = 0.056. The structure of niedermayrite is characterized by ∞ 2 [Cu4(OH)6O2]2− sheets of edgesharing Cu coordination octahedra parallel to (010) with attached SO4 tetrahedra, and intercalated CdO2(H2O)4 octahedra with a system of hydrogen bonds. Close relationships to the crystal structures of christelite and campigliaite exist. The new mineral is named for Dr. Gerhard Niedermayr, Naturhistorisches Museum Wien, Austria.