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Andreyivanovite: A second new phosphide from the Kaidun meteorite

¹ NASA Johnson Space Center, Code KT, Houston, Texas 77058, U.S.A.
² Muséum National d’Histoire Naturelle, 57 rue Cuvier, 75005 Paris Cedex, France
³ Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo-Ku, Tokyo 113, Japan
⁴ Institute of Materials Structure Science, Tsukuba-shi, Ibaraki-ken, 305, Japan
⁵ Jacobs Sverdrup Co., Houston, Texas 77058, U.S.A.
⁶ Graduate School of Life Science, University of Hyogo, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan

Correspondence: ^* E-mail: michael.e.zolensky{at}nasa.gov

Andreyivanovite (ideally FeCrP) is another new phosphide species from the Kaidun meteorite, which fell in South Yemen in 1980. Kaidun is a unique breccia containing an unprecedented variety of fragments of different chondritic as well as achondritic lithologies. Andreyivanovite was found as individual grains and linear arrays of grains with a maximum dimension of 8 µm within two masses of Fe-rich serpentine. In one sample, it is associated with Fe-Ni-Cr sulfides and florenskyite (FeTiP). Andreyivanovite is creamy white in reflected light, and its luster is metallic. The average of nine electron microprobe analyses yielded the formula Fe(Cr_0.587Fe_0.150V_0.109Ti_0.081Ni_0.060Co_0.002)P. Examination of single grains of andreyivanovite using Laue patterns collected by in situ synchrotron X-ray diffraction (XRD), and by electron-backscatter diffraction revealed it to be isostructural with florenskyite; we were unable to find single crystals of sufficient quality to perform a complete structure analysis. Andreyivanovite crystallizes in the space group Pnma, and has the anti-PbCl₂ structure. Previously determined cell constants of synthetic material [a = 5.833(1), b = 3.569(1), and c = 6.658(1) Å] were consistent with our XRD work. We used the XPOW program to calculate a powder-XRD pattern; the 5 most intense reflections are d = 2.247 (I = 100), 2.074 (81), 2.258 (46), 1.785 (43), and 1.885 Å (34). Andreyivanovite is the second new phosphide to be described from the Kaidun meteorite. Andreyivanovite could have formed as a result of cooling and crystallization of a melted precursor consisting mainly of Fe-Ni metal enriched in P, Ti, and Cr. Serpentine associated with andreyivanovite would then have formed during aqueous alteration on the parent asteroid. It is also possible that the andreyivanovite could have formed during aqueous alteration; however, artificial FeTiP has been synthesized only during melting experiments, at low oxygen fugacity, and there is no evidence that a hydrothermal genesis is reasonable.

Key Words: Andreyivanovite • electron diffraction • phosphide species • Kaidun meteorite