The new mineral bytizite was found in the dump of shaft No. 16, one of the mines in the Pr.ibram uranium and base-metal district, central Bohemia, Czech Republic. Bytizite is associated with chameanite, pr.ibramite, giraudite, berzelianite, umangite, eskebornite, hakite, tetrahedrite, bukovite, crookesite and uraninite in a calcite-dominant gangue. The new mineral occurs as anhedral grains up to 40 mu m, growing together in aggregates up to 300 mu m across. Bytizite is steel-grey in colour and has a metallic lustre. Mohs hardness is ca. 2-3; the calculated density is 6.324 g cm(3). In reflected light bytizite is grey with a yellowish hue, yellowish and brownish. Bireflectance and pleochroism are weak. Anisotropy is strong with grey to brownish rotation tints. Internal reflections were not observed. The empirical formula, based on electron-microprobe analyses, is (Cu3.00Fe0.01Ag0.01)(3.02)(Sb0.97As0.06)(1.03)Se-2.94. The ideal formula is Cu3SbSe3, which requires Cu 34.71, Sb 22.16 and Se 43.13, total 100.00 wt.%. Bytizite is orthorhombic, Pnma, a = 7.9594(12), b = 10.5830(14), c = 6.8240(11) angstrom, with V = 574.82(15) angstrom(3) and Z = 4. The strongest reflections of the calculated powder X-ray diffraction pattern [d, angstrom (I)(hkl)] are: 3.73(37)(210), 3.27(62)(211), 2.867 (40)(022), 2.698(100)(122) and 2.646(37)(040). According to the single-crystal X-ray diffraction data (R-obs = 0.0437), bytizite is isostructural with synthetic Cu3SbSe3. The structure of bytizite contains two Cu, one Sb, and two Se sites (the latter is occupied both by Se and S atoms). In the structure of both synthetic Cu3SbSe3 and bytizite, there are groups of three cis-edge-sharing tetrahedra [Cu3Se8], which are interlinked to a 3D framework by SbSe3 groups. Bytizite is named after its type locality, the Bytiz deposit, near the village Bytiz.
