Tetrahedrite-(Cd), Cu6(Cu4Cd2)Sb4S13, from Radětice near Příbram, Czech Republic: the new Cd member of the tetrahedrite group

Tetrahedrite-(Cd), Cu-6(Cu4Cd2)Sb4S13, is a new IMA-approved mineral species from Rad & ecaron;tice near the P & rcaron;& iacute;bram deposit, Czech Republic. It occurs as black metallic anhedral grains, up to 200 mu m in size in quartz-calcite gangue, associated with galena, bournonite, sphalerite, pyrite, geocronite, silver, stromeyerite, tetrahedrite-(Zn), tetrahedrite-(Fe), tetrahedrite-(Cu), and an unknown Pb-rich tetrahedrite-like phase. In reflected light, tetrahedrite-(Cd) is isotropic and grey with greenish tints. Reflectance data for the four COM wavelengths in air are as follows (lambda (nm) : R (%)): 470 : 30.8, 546 : 31.1, 589 : 31.1 and 650 : 28.8. Electron microprobe analysis gave (in wt % - average of 13 spot analyses) Cu 34.85, Ag 2.09, Fe 0.18, Zn 0.26, Cd 11.03, Hg 0.75, Pb 0.31, Sb 28.07, and S 23.38, with a total of 100.92. On the basis of Sigma Me = 16 atoms per formula unit, the empirical formula of tetrahedrite-(Cd) is Cu9.65Ag0.34Cd1.73Zn0.07Hg0.07Fe0.06Pb0.03Sb4.06S12.84. Tennantite-(Cd) is cubic, I(4) over bar 3m , with unit-cell parameters a=10.504(3) & Aring;, V=1158.9(9) & Aring;(3), and Z=2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R-1=0.0252 on the basis of 257 unique reflections with F-o>4 sigma(F-o) and 23 refined parameters. Tetrahedrite-(Cd) is isotypic with other tetrahedrite-group minerals. Its crystal chemistry is discussed, and previous findings of Cd-rich tetrahedrite-group minerals are briefly reviewed.