Metallic spheroids approximately 1 mm in diameter and having a dendritic structure appropriate to a rapidly solidified liquid alloy are encountered in conjunction with Canyon Diablo meteorites in the vicinity of the Barringer crater, Arizona. Compositionally and structurally similar particles have been encountered in lunar soils returned from Apollo 11, 12, 14, and 15 expeditions. The present study is devoted entirely to Canyon Diablo spheroids, which are shown by means of electron microprobe techniques to be enriched in Ni and considerably enriched in S and P relative to the metallic phases of Canyon Diablo meteorites. In contrast to earlier theories that considered only selective oxidation, a process of formation is now put forward involving the earlier stage of the shock-induced melting of sulphide-rich areas in the meteoritic projectile when it hits the earth. This process is also applicable to metallic spheroids formed on the moon, where oxidation processes will be minimal. Measuring the interarm spacing of the dendrites leads to estimates of 500°–30,000°C/sec for the rates at which these spheroids cooled through the solidification range. The breakup of the Canyon Diablo iron meteorite projectile is described by a series of events involving increasing shock pressures.