^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 [R_max/R_min, % (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, (Ni_1.72Fe_0.27)_1.99P_1.02, are: a = 5.8897(3), c = 3.3547(2) Å, V = 100.78(1) ų, Z = 3. D_calc = 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.

¹Patricia L. Clay,¹Katherine H. Joy,¹Brian O’Driscoll,¹Henner Busemann,¹Lorraine Ruzié-Hamilton,¹Ray Burgess,¹Jonathan Fellowes,²Bastian Joachim-Mrosko,¹John Pernet-Fisher,^3,4Stanislav Strekopytov, ⁵Christopher J. Ballentine
American Mineralogist 105, 289 – 306 Link to Article [https://doi.org/10.2138/am-2020-7237]
¹Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, U.K.
²Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52f, A-6020 Innsbruck, Austria
³Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London, SW7 5BD, U.K.
⁴National Measurement Laboratory, LGC Ltd, Queens Road, Teddington, TW11 0LY, U.K.
⁵Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, U.K.
Copyright: The Mineralogical Society of America

Volatile elements (e.g., H, C, N) have a strong influence on the physical and chemical evolution of planets and are essential for the development of habitable conditions. Measurement of the volatile and incompatible heavy halogens, Cl, Br, and I, can provide insight into volatile distribution and transport processes, due to their hydrophilic nature. However, information on the bulk halogen composition of martian meteorites is limited, particularly for Br and I, largely due to the difficulty in measuring ppb-level Br and I abundances in small samples. In this study, we address this challenge by using the neutron irradiation noble gas mass spectrometry (NI-NGMS) method to measure the heavy halogen composition of five olivine-phyric shergottite meteorites, including the enriched (Larkman Nunatak LAR 06319 and LAR 12011) and depleted (LAR 12095, LAR 12240, and Tissint) compositional end-members. Distinct differences in the absolute abundances and halogen ratios exist between enriched (74 to136 ppm Cl, 1303 to 3061 ppb Br, and 4 to 1423 ppb I) and depleted (10 to 26 ppm Cl, 46 to 136 ppb Br, and 3 to 329 ppb I) samples. All halogen measurements are within the ranges previously reported for martian shergottite, nakhlite, and chassignite (SNC) meteorites. Enriched shergottites show variable and generally high Br and I absolute abundances. Halogen ratios (Br/Cl and I/Cl) are in proportions that exceed those of both carbonaceous chondrites and the martian surface. This may be linked to a volatile-rich martian mantle source, be related to shock processes or could represent a small degree of heavy halogen contamination (a feature of some Antarctic meteorites, for example). The differences observed in halogen abundances and ratios between enriched and depleted compositions, however, are consistent with previous suggestions of a heterogeneous distribution of volatiles in the martian mantle. Depleted shergottites have lower halogen abundances and Br and Cl in similar proportions to bulk silicate Earth and carbonaceous chondrites. Tissint in particular, as an uncontaminated fall, allows an estimate of the depleted shergottite mantle source composition to be made: 1.2 ppm Cl, 7.0 ppb Br, and 0.2 ppb I. The resultant bulk silicate Mars (BSM) estimate (22 ppm Cl, 74 ppb Br, and 6 ppb I), including the martian crust and depleted shergottite mantle, is similar to estimates of the bulk silicate earth (BSE) halogen composition.