Annivite-(Zn), Cu6(Cu4Zn2)Σ6Bi4S13, from the Jáchymov ore district, Czech Republic: The first Bi-dominant member of the tetrahedrite group

Annivite-(Zn), Cu6(Cu4Zn2)Σ6Bi4S13, is a new IMA-approved mineral species from the Geister vein, Jáchymov ore district, Czech Republic. It occurs as anhedral grains, up to 50 m in size, and growth zones, up to 100 m in thickness, hosted by oscillatory zoned annivite-(Zn)/tennantite-(Zn) grains, and associated with Bi-rich tennantite-(Zn), tennantite-(Fe), tetrahedrite-(Zn), the not-yet approved 'annivite-(Fe)', bismuth, emplectite, wittichenite and supergene bismite, walpurgite and metazeunerite. In reflected light, annivite-(Zn) is isotropic, pale grey with a brownish shade and very rare pale brown internal reflections. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 32.3; 546: 32.0; 589: 32.0; 650: 31.6. Electron microprobe analysis gave (in wt.% - average of 5 spot analyses): Cu 36.29, Ag 0.14, Fe 0.08, Zn 7.11, Pb 0.19, As 6.07, Sb 4.50, Bi 21.08, S 23.68, total 99.14. On the basis of ΣMe =16 atoms per formula unit, the empirical formula of annivite-(Zn) is Cu10.13Ag0.02Zn1.93Fe0.03Pb0.02Bi1.79As1.43Sb0.66S13.10. Annivite-(Zn) is cubic, I 3m, with unit-cell parameters a = 10.3545(6) Å, V = 1110.16(19) Å3 and Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0493 on the basis of 278 unique reflections with Fo > 4σ(Fo) and 23 refined parameters. Annivite-(Zn) is isotypic with other tetrahedrite-group minerals. Its crystal chemistry is discussed, and previous findings of Bi-rich tetrahedrite-group minerals are briefly reviewed, along with the description of a second finding of annivite-(Zn) from the abandoned Mauritius tin mine, Hřebečná, Krušné hory Mountains, Czech Republic.