A new finding of ferdowsiite, ideally Ag8Sb5As3S16, from the Monte
Arsiccio mine, Apuan Alps, Tuscany (Italy) is reported. Ferdowsiite
occurs as black euhedral crystals, up to 0.3 mm in size, associated with
arsiccioite, boscardinite, and chabournéite in small vugs of baryte +
dolomite veins embedded in the pyrite-rich metadolostone close to
the contact with the baryte + pyrite ore body. Electron microprobe
data gave (wt% - mean of nine spot analyses): Ag 39.03(36), Pb 0.24(3),
As 10.63(18), Sb 26.57(9), S 23.71(14), Cl 0.04(1), total 100.22(41). On
the basis of ΣMe = 16 apfu, the chemical formula is Ag8.01(5)Pb0.03(1)
Sb4.83(2)As3.14(4)S16.36(15)Cl0.03(1). The crystal structure of ferdowsiite has
been refined in the space group P21/n, with unit-cell parameters a =
8.6573(4), b = 5.7896(3), c = 13.7866(7) Å, β = 96.122(2)°, V = 687.08(6)
Å3, Z = 1. The R1 factor converged to 0.024 on the basis of 1898 reflections
with Fo > 4σ(Fo) and 75 parameters
