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IIIAB Iron Meteorites
Description: Compared to the members of the IIIA subgroup, which have mostly coarse octahedrite textures, the IIIB iron meteorites usually display medium textures. Still, the members of both subgroups form a continuous sequence in structural and elemental compositions that suggests a common origin, probably representing different regions of an asteroid’s core.
Formation history & Origin: Some IIIAB members contain large nodules of troilite and graphite, but silicate inclusions are rare. Despite this fact, recent research suggests a close relationship exists between the IIIAB iron meteorites and the silicate-rich main group pallasites, some of the most attractive stony-iron meteorites known. Both groups probably formed on the same parent body, a differentiated asteroid that was disrupted by a single impact event. The IIIAB iron meteorites represent fragments of the core, while the MGPs do represent samples of the core/mantle boundary of their common parent body.
Members: With about 240 distinct members, group IIIAB certainly is the best-represented class of iron meteorites in our collections. Group IIIAB contains several prominent members representing some of the largest irons ever found. Just to name a few, there are the giants of Cape York, Chupaderos, Morito, and Willamette, the largest North American iron meteorite find.