Tsikourasite, Mo 3 Ni 2 P 1+ x ( x 0.25), a New Phosphide from the Chromitite of the Othrys Ophiolite, Greece

摘要

Tsikourasite, Mo 3 Ni 2 P 1+ x ( x 0.25), is a new phosphide discovered in a mantle-hosted podiform chromitite collected in the abandoned mine of Agios Stefanos (Othrys ophiolite), Central Greece. It forms tiny grains (from a few μm up to about 80 μm) and occurs as isolated grains or associated with other known minerals such as nickelphosphide and awaruite, and with undetermined minerals such as Ni-allabogdanite or Ni-barringerite and a V-sulphide. Tsikourasite is brittle and has a metallic luster. In plane-polarized light, tsikourasite is white yellow and it shows no bireflectance, anisotropism or pleochroism. Internal reflections were not observed, Reflectance values of tsikourasite in air ( R in %) are: 55.7 at 470 nm, 56.8 at 546 nm, 57.5 at 589 nm and 58.5 at 650 nm. Five spot analyses of tsikourasite give the average composition: P 7.97, S 0.67, V 14.13, Fe 14.37, Co 7.59, Ni 23.9, and Mo 44.16, total 99.60 wt.%, corresponding to the empirical formula (Mo 1.778 V 1.071 Fe 0.082 Co 0.069 ) Σ3.000 (Ni 1.572 Co 0.428 ) Σ2.000 (P 0.981 S 0.079 ) Σ1.060 , on the basis of Σ(Mo +V + Fe + Co + Ni) = 5 apfu and taking into account the structural results. The simplified formula is Mo 3 Ni 2 P 1+ x ( x 0.25). The density, which was calculated based on the empirical formula and single-crystal data, is 9.182 g/cm 3 . The mineral is cubic, space group F-43m, with a = 10.8215(5) ? and Z = 16. Although tsikourasite is similar in composition to those of monipite (MoNiP), polekhovskyite (MoNiP 2 ), and the synthetic compound MoNiP 2 , all these phases are hexagonal and not cubic like tsikourasite. It exhibits the same structure as the cubic Mo 3 Ni 2 P 1.18 compound [space group F-43m, a = 10.846(2) ?] synthesized at 1350 °C. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2018-156). The mineral honors Professor Basilios Tsikouras of the Universiti Brunei Darussalam.