Transjordanite, Ni2P, a new terrestrial and meteoritic phosphide, and natural solid solutions barringerite-transjordanite (hexagonal Fe2P–Ni2P)

1,2Sergey N. Britvin,1Michail N. Murashko,3Yevgeny Vapnik,1Yury S. Polekhovsky,1,2Sergey V. Krivovichev,1Maria G. Krzhizhanovskaya,1Oleg S. Vereshchagin,1,4Vladimir V. Shilovskikh,1Natalia S. Vlasenko
American Mineralogist 105, 428 – 436 Link to Article [https://doi.org/10.2138/am-2020-7275]
1St. Petersburg State University, Universitetskaya Nab. 7/9, 199034 St. Petersburg, Russia
2Kola Science Center, Russian Academy of Sciences, Fersman Str. 14, 184200 Apatity, Russia
3Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel
4Institute of Mineralogy, Urals Branch of Russian Academy of Science, Miass 456317, Russia
Copyright: The Mineralogical Society of America

This paper is a first detailed report of natural hexagonal solid solutions along the join Fe2P–Ni2P. Transjordanite, Ni2P, a Ni-dominant counterpart of barringerite (a low-pressure polymorph of Fe2P), is a new mineral. It was discovered in the pyrometamorphic phosphide assemblages of the Hatrurim Formation (the Dead Sea area, Southern Levant) and was named for the occurrence on the Transjordan Plateau, West Jordan. Later on, the mineral was confirmed in the Cambria meteorite (iron ungrouped, fine octahedrite), and it likely occurs in CM2 carbonaceous chondrites (Mighei group). Under reflected light, transjordanite is white with a beige tint. It is non-pleochroic and weakly anisotropic. Reflectance values for four COM recommended wavelengths are [Rmax/Rmin, % (λ, nm)]: 45.1/44.2 (470), 49.9/48.5 (546), 52.1/50.3 (589), 54.3/52.1 (650). Transjordanite is hexagonal, space group P62m; unit-cell parameters for the holotype specimen, (Ni1.72Fe0.27)1.99P1.02, are: a = 5.8897(3), c = 3.3547(2) Å, V = 100.78(1) Å3, Z = 3. Dcalc = 7.30 g/cm3. The crystal structure of holotype transjordanite was solved and refined to R1 = 0.013 based on 190 independent observed [I > 2σ(I)] reflections. The crystal structure represents a framework composed of two types of infinite rods propagated along the c-axis: (1) edge-sharing tetrahedra [M(1)P4] and (2) edge-sharing [M(2)P5] square pyramids. Determination of unit-cell parameters for 12 members of the Fe2P–Ni2P solid-solution series demonstrates that substitution of Ni for Fe in transjordanite and vice versa in barringerite does not obey Vegard’s law, indicative of preferential incorporation of minor substituent into M(1) position. Terrestrial transjordanite may contain up to 3 wt% Mo, whereas meteoritic mineral bears up to 0.2 wt% S.

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