Orishchinite, a new terrestrial phosphide, the Ni-dominant analogue of allabogdanite

Orishchinite is a new terrestrial phosphide discovered in pyrometamorphic rocks of the Daba-Siwaqa combustion complex in West Jordan. The mineral occurs as an accessory phase in the fused clinopyroxene-plagioclase rock (paralava) texturally resembling gabbro-dolerite. Orishchinite forms resorbed equant grains up to 0.2 mm outrimmed with 0.1–0.2 thick zones of substituting murashkoite, FeP. Chemical composition (electron microprobe, wt%): Ni 38.49, Fe 22.38, Co 0.47, Mo 18.80, P 19.46, Total 99.60, corresponding to the empirical formula (Ni 1.04 Fe 0.64 Mo 0.31 Co 0.01 ) Σ2.00 P on the basis of 3 apfu . The simplified formula is (Ni,Fe,Mo) 2 P and the ideal one is Ni 2 P. Macroscopically, orishchinite grains have yellowish-white colour with metallic lustre. The mineral is brittle. In reflected light, orishchinite is yellowish-white and non-pleochroic. It is very weakly anisotropic (Δ R 589 = 1.3%). Reflectance values for the wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are [ R max / R min (%), λ (nm)]: 48.1/47.5, 470; 50.6/49.4, 546; 52.1/50.8, 589; 54.4/52.9.1, 650. The crystal structure was solved and refined to R 1 = 0.016 based on 224 unique observed [ I ≥ 2σ( I )] reflections. Orishchinite is orthorhombic, space group Pnma , a 5.8020(7), b 3.5933(4), c 6.7558(8) Å, V 140.85(3) Å 3 , Z = 4, D x = 7.695 g cm -3 . The strongest lines of the powder X-ray diffraction pattern [( d , Å) ( I , %) ( hkl )] are: 2.265(100)(112), 2.201(16)(202), 2.142(55)(211), 2.100(35)(103), 1.909(21)(013), 1.811(19)(113), 1.796(31)(020). Orishchinite is dimorphous with transjordanite (hexagonal Ni 2 P) and can be considered the Ni-dominant analogue of allabogdanite.