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The paper describes the general requirements for a genetically significant scheme for classifying iron meteorites. Some of the properties which may be used to classify iron meteorites are reviewed, and a classification scheme based on Ga-Ni and Ge-Ni plots, taxonomic properties, and chemical properties is proposed. It is found that 95% of the irons can be assigned to a genetic group or an anomalous class.
Ni3Ga is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded to eight Ni and four equivalent Ga atoms to form distorted NiGa4Ni8 cuboctahedra that share corners with twelve equivalent NiGa4Ni8 cuboctahedra, edges with eight equivalent GaNi12 cuboctahedra, edges with sixteen NiGa4Ni8 cuboctahedra, faces with four equivalent GaNi12 cuboctahedra, and faces with fourteen NiGa4Ni8 cuboctahedra. There are four shorter (2.49 Å) and four longer (2.60 Å) Ni–Ni bond lengths. All Ni–Ga bond lengths are 2.49 Å. In the second Ni site, Ni is bonded to eight equivalent Ni and four equivalent Ga atoms to form NiGa4Ni8 cuboctahedra that share corners with four equivalent NiGa4Ni8 cuboctahedra, corners with eight equivalent GaNi12 cuboctahedra, edges with twenty-four NiGa4Ni8 cuboctahedra, faces with six equivalent GaNi12 cuboctahedra, and faces with twelve NiGa4Ni8 cuboctahedra. All Ni–Ga bond lengths are 2.60 Å. Ga is bonded to twelve Ni atoms to form GaNi12 cuboctahedra that share corners with four equivalent GaNi12 cuboctahedra, corners with eight equivalent NiGa4Ni8 cuboctahedra, edges with eight equivalent GaNi12 cuboctahedra, edges with sixteen equivalent NiGa4Ni8 cuboctahedra, faces with four equivalent GaNi12 cuboctahedra, and faces with fourteen NiGa4Ni8 cuboctahedra.