Nickolayite, FeMoP, a new natural molybdenum phosphide

Nickolayite, FeMoP, is a new terrestrial phosphide structurally related to allabogdanite (high-pressure modification of (Fe,Ni)(2)P), and the meteoritic phosphides florenskyite, FeTiP and andreyivanovite, FeCrP. From the point of view of chemical composition, nickolayite is an Fe-analogue of monipite, MoNiP. The mineral was discovered in the Daba-Siwaqa complex, Central Jordan, a part of the pyrometamorphic Hatrurim Formation (the Mottled Zone), whose outcrops encompass a 150 x 200 km area around the Dead Sea in the Middle East. Nickolayite appears as an accessory phase in the fused clinopyroxene-plagioclase rocks texturally resembling gabbro-dolerite. The irregularly shaped grains of the mineral, up to 80 mu m in size are associated with baryte, tridymite, chromite, hematite, pyrrhotite, fluorapatite, titanite and powellite. Macroscopically, nickolayite grains possess light-grey to greyish-white colour and metallic lustre. The mineral is ductile. The mean VHN hardness (50 g load) is 538 kg mm(-2). The calculated density based on the empirical formula and the unit-cell parameters is 7.819 g cm(-1). In reflected light, nickolayite has a white colour, with no bireflectance or pleochroism. The COM approved reflectance values [R-max/R-min (%), lambda(nm)] are: 48.5/46.5 (470), 50.5/48.5 (546), 51.8/49.9 (589) and 53.9/52.0 (650). The chemical composition of the holotype crystal is (electron microprobe, average of 4 analyses, wt.%): Fe 32.21, Mo 47.06, Ni 3.69, Co 0.13, P 17.45, total 100.54, that corresponds to the empirical formula Fe-1.00(Mo0.87Ni0.11Fe0.02)(sigma 1.00)P-1.00 and an ideal formula of FeMoP. Nickolayite is orthorhombic, space group Pnma, unit-cell parameters of holotype material are: a = 5.9519(5), b = 3.7070(3), c = 6.8465(6) angstrom, V = 151.06(2) angstrom(3) and Z = 4. The crystal structure of holotype material was solved and refined to R-1 = 0.0174 based on 251 unique observed reflections. The origin of the mineral is probably connected to the processes of co-reduction of molybdenum- and phosphorus-bearing minerals during high-temperature pyrometamorphic processes.

Automated summary

Nickolayite, a new mineral, is structurally related to other minerals. It was discovered in the Daba-Siwaqa complex in Jordan, which is associated with the Hatrurim Formation. Nickolayite appears as an accessory phase in rocks and has irregularly shaped grains with a greyish-white color and metallic luster. The mineral is likely formed through co-reduction of molybdenum and phosphorus-bearing minerals during high-temperature pyrometamorphic processes.