Gobelinite, the Co analogue of ktenasite from Cap Garonne, France, and Eisenzecher Zug, Germany

The new mineral gobelinite, ideally CoCu4(SO4)(2)(OH)(6)center dot 6H(2)O, is a new member of the ktenasite group and the Co analogue of ktenasite, ZnCu4(SO4)(2)(OH)(6)center dot 6H(2)O. It occurs at Cap Garonne (CG), Var, France (type locality), and Eisenzecher Zug (EZ), Siegerland, North Rhine-Westphalia, Germany (cotype locality). The mineral forms pale green, bluish green or greyish green, blocky to thin, lath-like crystals. They are transparent and non-fluorescent, with a vitreous, sometimes also pearly, lustre and a white streak having a pale-green cast. Mohs hardness is about 2.5. The crystals are brittle with an irregular fracture; no cleavage was observed. D(meas.) is 2.95(2) and D(calc.) is 2.907 g cm(-3) (for empirical formula, CG). Common associates are brochantite and various other hydrated metal sulfates. Electron-microprobe analyses of the CG material yielded (wt. %) CuO 42.45, CoO 6.58, NiO 3.37, ZnO 3.14, SO3 22.12, and H2O 22.62 (calculated on structural grounds), and total = 100.30 wt. %, giving the empirical formula (based on 20 0 atoms) (Co0.63Ni0.32Zn0.28CU3.83)(Sigma)5.06S1.98O20H18.00. The simplified formula is (Co,Ni)(Cu,Zn)(4)(SO4)(2)(OH)(6)center dot 6H(2)O, and the endmember formula is CoCu4(SO4)(2)(OH)(6)center dot 6H(2)O. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses of the (Zn-free) EZ material gave the simplified average formula (Co0.92Ni0.21Mg0.01Cu3.79)(Sigma 4.93)(SO4)(2.08)(OH)(6)center dot 6H(2)O. Optically, gobelinite (CG) is biaxial negative, with alpha = 1.576(2), beta = 1.617(2) and gamma = 1.630(2); 2V(meas) = 58(4)degrees and 2 V-calc = 57.5 degrees. Dispersion is weak, r > v; orientation is X = beta, Y = gamma and Z approximate to alpha, with strong pleochroism X equaling colourless, Y equaling green and Z equaling pale green. The mineral is monoclinic, space group P2(1)/c, with a = 5.599(1), b = 6.084(1), c = 23.676(5) angstrom, beta = 95.22(3)degrees and V = 803.2(3) angstrom(3) (at 100 K; CG) and a = 5.611(1), b = 6.103(1), c = 23.808(5) angstrom, beta = 95.18 (3)degrees and V = 811.9(3) angstrom(3) (at 298 K; EZ), respectively (Z = 2). The eight strongest measured powder X-ray diffraction lines (d in angstrom (I) hkl (CG material)) are 11.870 (100) 002, 5.924 (40) 004, 4.883 (10) 102, 4.825 (15) 013, 3.946 (15) 006, 2.956 (15) 008, 2.663 (20) 202 and 2.561 (15) (1) over bar 23. Single-crystal structure determinations gave R-1 = 0.0310 (CG) and 0.0280 (EZ). The atomic arr