Abstract:
Lemanskiite, ideally NaCaCu5(AsO4) 4Cl·5H2O, is a new mineral species from the Abundancia mine, El Guanaco mining district, Chile. It is dimorphous with lavendulan and represents the Ca-analogue of zdenekite. It occurs as rosette-shaped aggregates (up to 5 mm) of thin lamellar, subparallel, strongly bent intergrowths (0.3 mm × 10 μm) or needle-shaped aggregates of 0.8 mm length and 10 μm in thickness. Individual thin tabular crystals (up to 4 mm in length) are invariably bent. It is associated with lammerite, olivenite, mansfieldite, senarmontite, a mineral of the crandallite group, rutile, anatase, and talc. Lemanskiite is dark sky blue, translucent, nonfluorescent with a light blue streak. It is brittle with an excellent cleavage parallel to (001); its luster is vitreous, and its Mohs hardness is ~21/2. The mineral displays no parting, and its fracture is uneven. It is optically negative, uniaxial, with indices ε = 1,647(2) and ω = 1.749(2); its birefrigence is 0.102, and the pleochroism is very strong. The compatibility index is superior (0.009). An electron-microprobe analysis revealed the following chemical composition (in wt.%): CaO 5.33(7), Na2O 3.04(18), CuO 37.76(44), As2O5 43.53(59), Cl 3.23(7). The content of H2O (8.50 wt.%) was determined with a CHN analyzer. The empirical formula based on 22 anions is Na1.04 Ca1.00Cu5.01 (AsO4) 4.00 [Cl0.96 (OH)0.11]∑1.07 ·4.93 H2O. Crystallographic data were derived from the data on zdenekite. The whole-powder-pattern fitting assuming the tetragonal space-group P4122 (or P4322) gave the following parameters: a 9.9758(4), c 36.714(1) Å, V 3653.6(2) Å3, with Z = 8, Dx = 3.863(5), and Dm = 3.78(1) g/cm3. The strongest five lines in the X-ray powder pattern [d in Å (I)(hkl)] are: 9.60(9)(101), 9.177(100)(004), 4.588(32)(008), 4.167(10)(108), 3.059(15)(0.0.12). The name honors Chester S. Lemanski, Jr. (b. 1947), mineral collector who built one of the largest privately held collections in the USA. Both the mineral and its name have been approved by the Commission on New Minerals and Mineral Names (IMA 99-037).
