MINERALOGICAL RELATIONSHIPS IN SEYMOUR,A COARSE OCTAHEDRITE

Seymour is a coarse octahedrite weighing 24.5 kg. It contains two types of troilite-graphite nodules (massive graphite nodules with irregular troilite rims, and troilite nodules with irregular, partial or total, rims of graphite); four morphologically distinct types of phosphide (lamellar, swathing, grain boundary, and rhabdite); and three types of cohenite (lamellar, swathing, and inclusions in kamacite). It is believed that lamellar and swathing schreibersite crystallized from taenite at approximately 900°C. This was followed by the crystallization of kamacite, then the development of cohenite, and finally a second period of phosphide nucleation giving rise to grain boundary schreibersite and rhabdite. Compositional data indicates that grain boundary schreibersite and rhabdite grew simultaneously.