Pizgrischite, (Cu,Fe)Cu14PbBi17S35, is a new mineral species named after
the type locality, Piz Grisch Mountain, Val Ferrera, Graubunden,
Switzerland. This sulfosalt occurs as thin, striated, metallic lead-grey
blades measuring up to I cm in length, embedded in quartz and associated
with tetrahedrite, chalcopyrite, pyrite, sphalerite, emplectite and
derivatives of the aikinite-bismuthinite series. In plane-polarized
light, the new species is brownish grey with no perceptible pleochroism;
under crossed nicols in oil immersion, it presents a weak anisotropy
with dark brown tints. Minimum and maximum reflectance values (in %) in
air are: 40.7-42.15 (470 nm), 41.2-43.1 (546 nm), 41.2-43.35 (589 nm)
and 40.7-43.3 (650 nm). Cleavage is perfect along 001 I and well
developed on {010}. Abundant polysynthetic twinning is observed on
(010). The mean micro-indentation hardness is 190 kg/mm(2) (Mohs
hardness 3.3), and the calculated density is 6.58 g/cm(3).
Electron-microprobe analyses yield (wt%; mean result of seven
analyses): Cu 16.48, Pb 2.10, Fe 0.77, Bi 60.70, Sb 0.35, S 19.16, Se
0.04, total 99.60. The resulting empirical chemical formula is
(Cu15.24Fe0.80Pb0.60)(Sigma 16.64)(Bi17.07Sb0.17)(Sigma
17.24)(S35.09Se0.03)(Sigma 35.12), in accordance with the formula
derived from the single-crystal refinement of the structure,
(Cu,Fe)Cu14PbBi17S35. Pizgrischite is monoclinic, space group C2/m, with
the following unit-cell parameters: a 35.054(2), b3.91123(I), c43.192(2)
angstrom, beta 96.713(4)degrees, V5881.24 angstrom(3), Z=4. The
strongest seven X-ray powder-diffraction lines [d in angstrom
(I)(hkl)] are: 5.364(40)((6) over bar 04), 4.080(50)((8) over bar 05),
3.120(40)(118), 3.104(68)((3) over bar 18), 2.759(53) ((9) over bar
11),2.752(44)(910) and 1.956(100)(020). The crystal structure is an
expanded monoclinic derivative of kupcikite. Pizgrischite belongs to the
cuprobismutite series of bismuth sulfosalts but, sensu stricto, it is
not a homologue of cuprobismutite. At the type locality. pizarischite is
the result of the Alpine metamorphism under greenschist-facies
conditions of pre-Tertiary hydrothermal Cu-Bi mineralization.