IAB complex
A large, chemically scattered family of iron meteorites, many carrying silicate, graphite and sulfide inclusions.
The IAB complex is one of the largest assemblages of iron meteorites, made up of a main group and several subgroups defined by nickel, gold and other trace elements. Unlike magmatic irons, its members do not follow tight fractional-crystallisation trends, which is why it is described as non-magmatic. Many IAB irons contain nodules of graphite and troilite, and some carry angular silicate inclusions whose minerals and oxygen isotopes resemble the primitive achondrites called winonaites.
Its origin is still debated. One family of models proposes that impacts on a partly differentiated, chondrite-like body produced pools of metallic melt that cooled with trapped rock fragments, rather than forming a single core. Two classic main-group members are Canyon Diablo, the iron that made Meteor Crater in Arizona, and Campo del Cielo from Argentina, both coarse octahedrites. Toluca from Mexico and Odessa from Texas are other examples.
In practice, IAB irons are often coarse octahedrites with abundant schreibersite, cohenite and graphite visible on etched slices. Assignment to the complex and to a specific subgroup depends on bulk trace-element analysis.
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