Iron Meteorite

Iron meteorites consist mostly of metallic iron alloyed with typically between ~5 to ~30 wt% nickel. The main metal phases are kamacite α-(Fe, Ni) and taenite y-(Fe, Ni). Based on their group classification, they may also contain a small weight percentage of one or more of the following minerals:

  1. Graphite, typically in the form of nodules: C
  2. Troilite, (iron sulfide): FeS
  3. Schreibersite: (Fe,Ni)3P
  4. Cohenite: (Fe,Ni,Co)3C
  5. Various silicate inclusions and other minerals.

Iron meteorites are classified into various chemical groups that fall into 3 general types based on their texture driven by their nickel (Ni) content:

  1. Hexahedrite: Ni < 6%
  2. Octahedrite: 6% < Ni < 16
  3. Ni-Rich Ataxite: Ni > 16%

Iron meteorites containing >16% Ni nucleate kamacite at such low temperatures that large single crystals could not form over the 4.55 billion years of solar system history; they lack a Widmanstätten pattern and are called Ni-rich ataxites (i.e. without structure). The Ni-poor ataxites are hexahedrites or octahedrites reheated in massive impacts, or artificially after they fell on Earth. (https://www.sciencedirect.com/book/9780124158450/encyclopedia-of-the-solar-system)

Iron meteorite with the highest bulk Ni content: Oktibbeha County (58.5 wt% to ~60 wt%)
Other notable high bulk Ni content iron meteorites: NWA 6259 (42.2 wt%), Santa Catharina (35.3%), Tishomingo (32.5 wt%)

Group IC is a cohenite-rich group

No iron meteorite contains less than 5% Ni. ???? from Handbook