Iron, IAB-complex, Modifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung).
As described by R. Haag (1992), this Work in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and was discovered by a prospector using a metal-detector to search for gold in a mining region of Queensland, Australia. As few as four small, weathered masses of this unusual iron were found scattered over an area of a quarter of a mile; the combined weight of the fragments was 5 kg. Georgetown contains an abundance of sinuous FeS (Brass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites.) ribbons throughout the FeNi-metal host, thought to have been trapped during an impact-melt event. Alternative mechanisms for concentrating troilite in FeNi-metal have been suggested, such as by co-crystallization in a S-saturated Molten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava., possibly involving volatile-driven migration of FeNi–FeS blebs into large channels (Kracher, 1985).
Diagram credit: Worsham et al., GCA, vol. 188, p. 269 (2016)
‘Literally, "iron-loving" element that tends to be concentrated in Fe-Ni metal rather than in silicate; these are Fe, Co, Ni, Mo, Re, Au, and PGE. These elements are relatively common in undifferentiated meteorites, and, in differentiated asteroids and planets, are found in the metal-rich cores and, consequently, extremely rare on systematics of IAB complex iron meteorites: New insights into the formation of an enigmatic group’
(https://doi.org/10.1016/j.gca.2016.05.019) The O-isotope data for Georgetown suggest that the precursor material was a metal-rich, FeS-rich, Carbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than, perhaps similar to the Class named for the Renazzo meteorite that fell in Italy in 1824, are similar to CMs in that they contain hydrous silicates, traces of water, and magnetite. The main difference is that CRs contain Ni-Fe metal and Fe sulfide that occurs in the black matrix and in the large chondrules The body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today.. Impact-melting was responsible for the segregation of sulfides from Element that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn, and the initially high FeS content likely sustained the melting process at lower temperatures (Choi et al., 1994). The photo above shows a 47.2 g etched slice of Georgetown exhibiting abundant troilite.