Kudriavite, (Cd,Pb)Bi2S4, a new mineral species from Kudriavy volcano, Iturup Island, Kurile arc, Russia

Kudriavite, a new mineral species. occurs as a high-temperature (about 400 degrees C) fumarole incrustation in the steep inner wall of the crater rim of Kudriavy volcano, on Iturup Island, in the Kurile arc, Russia. Associated minerals are cannizzarite, greenockite and pyrite. The mineral occurs as elongate slender platy opaque crystals up to 0.4 x 0.2 x 0.02 mm, usually striated along the elongation. Box-shaped skeletal crystals also are common. The color is dark grey, with a slightly reddish hue and a metallic luster. The streak is black. Crystals of kudriavite have an uneven fracture and are very brittle. Reflectance values for the COM wavelengths [% (R-1, R-2)] are: 470 nm (36.4, 29.6), 546 mn (38.8, 32.4), 589 nm (38.2, 31.8), and 650 nm (37.7. 31.4). The bireflectance is distinct the anisotropy is rather strong, but without color effect. Its measured microhardness VHN10 is 129. The electron-microprobe analysis of holotype kudriavite gave Cd 8.25, Pb 13.10, Fe 0.17, Mn 0.26, Bi 55.37, In 2.80, TI 0.02, S 17.70, Se 2.23, Cl 0.02, sum 99.92 wt.%. The empirical formula, based on seven atoms, is (Cd0.51Pb0.44Fe0.02Mn0.03)(Sigma 1.00) (Bi-1.83 In-0.17)(Sigma 2.00) (S3.81Se0.19)(Sigma 4.00); the idealized formula is (Cd,Pb)Bi2S4. The ideal formula CdBi2S4 requires Cd 17.07, Bi 63.46, S 19.47, for a total of 100.00 wt.%. The strongest nine lines of the X-ray powder-diffraction pattern [d in angstrom(l)(hkl)] are: 3.715(m)(202), 3.632(m)(204), 3.520(s)((1) over bar 12), 3.274(s)(004,(4) over bar 02), 3.169(m)(112), 2.948(s) ((3) over bar 11), 2.809(s)(310), 2.346(m)(114, (1) over bar 15), and 1.914(m)(511). The unit-cell parameters of kudriavite, determined on a single crystal, are: a 13.095(1), b 4.0032(3), c 14.711(l) angstrom, beta 115.59(1)degrees, V 695.5(1) angstrom(3), Z = 4, space group C2/m, D-calc = 6.578 g/cm(3). According to the solution of the structure, kudriavite is the first natural homologue N = 3 of pavonite. The mineral (IMA No. 2003-011) is named after the discovery locality.