Abstract. Gersdorffite, ideally NiAsS, and associated minerals from
Contrada Zillì (Peloritani Mountains, Sicily, Italy) have been
characterized through electron microprobe analysis and X-ray diffraction.
Primary minerals, hosted in quartz veins, are represented by gersdorffite,
tetrahedrite-(Fe), and chalcopyrite with minor pyrite and galena. Rare
aikinite inclusions were observed in tetrahedrite-(Fe) and chalcopyrite.
Gersdorffite occurs as euhedral to subhedral crystals, up to 1 mm in size,
with (Sb,Bi)-enriched cores and (Fe,As)-enriched rims. Its chemical
composition is
(Ni0.79−0.95Fe0.18−0.04Co0.04−0.01)(As0.90−1.03Sb0.10−0.00Bi0.02−0.00)S0.98−0.92.
It crystallizes in the space group P213, with unit-cell parameters a=5.6968(7) Å, V=184.88(7) Å3, and Z=4, and its crystal
structure was refined down to R1= 0.035. Associated tetrahedrite-(Fe)
has chemical formula (Cu5.79Ag0.07)Σ5.86(Cu3.96Fe1.59Zn0.45)Σ6.00(Sb3.95As0.17Bi0.03)Σ4.15S13.06, with unit-cell parameters a= 10.3815(10) Å, V=1118.9(3) Å3, and space group I-43m. Its crystal structure was
refined to R1=0.027. Textural and crystallographic data suggest a
polyphasic crystallization of gersdorffite under low-temperature conditions.