Miharaite, Cu₄FePbBiS₆, a new mineral from the Mihara mine, Okayama, Japan

Miharaite, Cu₄FePbBiS₆, is a new sulfosalt discovered at the Mihara mine, Okayama Prefecture, Japan. It occurs only as minute (<0.3 mm) grains in bomite, closely associated with chalcopyrite, galena, and wittichenite in bomite-rich skarn ores. The crystallographic parameters of miharaite at 25°C are: orthorhombic, space group Pbmm, Pb2m, or Pb2₁m, a = 10.854(4), b = 11.985(4), c = 3.871(1)Å, Z = 2, cell volume = 503.6(3)ų. The strongest lines in the X-ray powder pattern are 3.75(60)(130), 3.25(70)(021), 3.11(55)(320), 3.03(100)(211), 3.00(90)(040), 2.68(80)(301), 2.18(60)(411). The calculated density is 6.06 g/cm³. In reflected light, it is pale gray to grayish-white with slight bireflectance and moderate anisotropism from grayish-blue to pinkish-brown. The optical properties are quite similar to those of wittichenite. Reflectances in air are: 29.6–30.0% in 480 nm, 30.8–31.5% in 546 nm, 31.7–32.6% in 589 nm, 32.1–34.2% in 657 nm. Vickers microhardness is 190–230 kg/cm². The average of six microprobe analyses gave Cu_4.09Fe_1.00Pb_1.01Bi_1.00S_5.91 as an empirical formula, very close to the proposed formula Cu₄FePbBiS₆.