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A nonmagmatic origin of group-IIE iron meteorites

New neutron activation data on 10 elements in 12 IIE and IIE-related irons lead to a reclassification of several irons. Seymchan and Lonaconing are removed from IIE, and Leshan added. Four IIE members are designated IIE-An to call attention to some anomalous properties. The eight normal IIE members define element-Ni trends generally similar to those in the nonmagmatic group IAB; the small negative slopes on W-Ni and Ir-Ni diagrams are strongly indicative of a nonmagmatic origin of the IIE irons. It is proposed that IIE irons like IAB irons originated as individual pools of impact-produced melt in the near-surface region of a chondritic parent body. The positive As-Ni and Au-Ni trends are the only evidence suggesting fractional crystallization, but their slopes are lower than those in magmatic group IIIAB, and only slightly higher than those of Cu and Sb in IAB. It is suggested that the S and C contents of the IIE precursor materials were much lower than those of the IAB precursors, thus higher temperatures were required to generate enough metallic melt to segregate into pools. These higher temperatures are also reflected in the nonchondritic compositions of the silicate inclusions.

Wasson, J. T.↗

Materials Data on NiIr by Materials Project

IrNi crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Ir sites. In the first Ir site, Ir is bonded to six equivalent Ir and six equivalent Ni atoms to form distorted IrNi6Ir6 cuboctahedra that share corners with twelve IrNi6Ir6 cuboctahedra, edges with twelve IrNi6Ir6 cuboctahedra, edges with twelve equivalent NiNi6Ir6 cuboctahedra, faces with six equivalent IrNi6Ir6 cuboctahedra, and faces with twelve equivalent NiNi6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.68 Å. All Ir–Ni bond lengths are 2.60 Å. In the second Ir site, Ir is bonded to six equivalent Ir and six Ni atoms to form distorted IrNi6Ir6 cuboctahedra that share corners with five equivalent NiNi10Ir6 cuboctahedra, corners with twelve IrNi6Ir6 cuboctahedra, edges with ten NiNi6Ir6 cuboctahedra, edges with twelve IrNi6Ir6 cuboctahedra, faces with six equivalent IrNi6Ir6 cuboctahedra, and faces with fifteen NiNi6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.68 Å. All Ir–Ni bond lengths are 2.60 Å. In the third Ir site, Ir is bonded to six equivalent Ir and six Ni atoms to form distorted IrNi6Ir6 cuboctahedra that share corners with five equivalent NiNi10Ir6 cuboctahedra, corners with twelve IrNi6Ir6 cuboctahedra, edges with ten NiNi6Ir6 cuboctahedra, edges with twelve IrNi6Ir6 cuboctahedra, faces with six equivalent IrNi6Ir6 cuboctahedra, and faces with fifteen NiNi6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.68 Å. All Ir–Ni bond lengths are 2.60 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded to six Ir and six equivalent Ni atoms to form distorted NiNi6Ir6 cuboctahedra that share corners with twelve NiNi6Ir6 cuboctahedra, edges with twelve IrNi6Ir6 cuboctahedra, edges with twelve NiNi6Ir6 cuboctahedra, faces with six equivalent NiNi6Ir6 cuboctahedra, and faces with twelve IrNi6Ir6 cuboctahedra. All Ni–Ni bond lengths are 2.68 Å. In the second Ni site, Ni is bonded to six Ir and ten equivalent Ni atoms to form distorted NiNi10Ir6 cuboctahedra that share corners with ten IrNi6Ir6 cuboctahedra, corners with twelve NiNi6Ir6 cuboctahedra, edges with eight IrNi6Ir6 cuboctahedra, edges with sixteen NiNi6Ir6 cuboctahedra, faces with sixteen equivalent NiNi10Ir6 cuboctahedra, and faces with eighteen IrNi6Ir6 cuboctahedra. There are a spread of Ni–Ni bond distances ranging from 2.68–5.35 Å.

36 MATERIALS SCIENCE↗

Materials Data on NiIr3 by Materials Project

Ir3Ni is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ir sites. In the first Ir site, Ir is bonded to eight Ir and four equivalent Ni atoms to form IrNi4Ir8 cuboctahedra that share corners with twelve equivalent IrNi4Ir8 cuboctahedra, edges with eight equivalent NiIr12 cuboctahedra, edges with sixteen IrNi4Ir8 cuboctahedra, faces with four equivalent NiIr12 cuboctahedra, and faces with fourteen IrNi4Ir8 cuboctahedra. There are four shorter (2.68 Å) and four longer (2.69 Å) Ir–Ir bond lengths. All Ir–Ni bond lengths are 2.69 Å. In the second Ir site, Ir is bonded to eight equivalent Ir and four equivalent Ni atoms to form IrNi4Ir8 cuboctahedra that share corners with four equivalent IrNi4Ir8 cuboctahedra, corners with eight equivalent NiIr12 cuboctahedra, edges with twenty-four IrNi4Ir8 cuboctahedra, faces with six equivalent NiIr12 cuboctahedra, and faces with twelve IrNi4Ir8 cuboctahedra. All Ir–Ni bond lengths are 2.68 Å. Ni is bonded to twelve Ir atoms to form NiIr12 cuboctahedra that share corners with four equivalent NiIr12 cuboctahedra, corners with eight equivalent IrNi4Ir8 cuboctahedra, edges with eight equivalent NiIr12 cuboctahedra, edges with sixteen equivalent IrNi4Ir8 cuboctahedra, faces with four equivalent NiIr12 cuboctahedra, and faces with fourteen IrNi4Ir8 cuboctahedra.

36 MATERIALS SCIENCE↗