부산대학교 도서관

Slikite, Zn2Mg(CO3)2(OH)2·4H2O is a new supergene post-mining mineral from the Jachymov (formerly St. Joachimsthal) ore district, Czech Republic, associated with brianyoungite, hexahydrite, hydromagnesite, nesquehonite, serpierite, smithsonite and a ktenasite-like mineral. It forms snow-white radial aggregates, up to 2 mm across, in vugs or on surfaces of fragments of skarn rocks. Individual crystals are very thin blades, elongated along [110] and flattened on {001}, up to 200 µm in length. Slikite has a white streak, a vitreous lustre, and does not fluoresce under either short- or long-wave ultraviolet light. Cleavage is perfect on {001}, the Mohs hardness is ∼2, and the fracture is uneven. The mineral is brittle, although thin blades (fibres) are slightly flexible. The calculated density is 2.613 g/cm3. Slikite is optically biaxial negative, the indices of refraction are α=1.50(1), β=1.55(1), γ=1.59(1) and 2Vmeas.=80(1)°. The mineral is triclinic, space group P-1, a=6.335(4), b=6.340(1), c=13.923(4)Å, α=99.985(7)°, β=92.74(1)°, γ=114.93(2)°, V=494.8(4)Å3, Z=2. The seven strongest lines in the X-ray powder diffraction pattern are [d (Å)/I(hkl)]: 13.575/100(001), 4.525/31(003), 3.573/2(113), 3.406/5(111), 2.996/3(113) and 2.773/3(112). The chemical analyses by electron microprobe yielded MgO 8.39, ZnO 46.28, CuO 0.05, MnO 0.68, CdO 0.04, CO2calc. 23.10, H2Ocalc. 23.65, total 102.19 wt%. The empirical formula on the basis of 12 O atoms per formula unit is Zn2.00(Mg0.79Zn0.17Mn0.04)Σ1.00(CO3)2(OH)2·4H2O. The crystal structure of Slikite was refined using synchrotron single-crystal data to Robs=0.094 for 1594 reflections with I > 3σ(I). The structure of Slikite is based on heteropolyhedral layers of composition [Zn4Mg(CO3)4(OH)4]2-, parallel to {001}, with interlayer H-bonded [Mg(H2O)6]2+ and H2O. Within the layers, [110] chains of corner-connected ZnO2(OH)2 tetrahedra share corners with Mg-centred octahedra. The two types of polyhedra are connected via CO3 groups. The Raman and infrared spectra of Slikite as well as tentative assignment of observed bands are given in this paper. The mineral is named in honour of the prominent Czech aristocrat Stepan Slik (1487-1526), founder of town St. Joachimsthal (now Jachymov).