Pallasite

One of two main classes of stony-iron meteorite, the other being mesosiderites. Pallasites are igneous in nature and characterized by crystals of olivine, sometimes peridot (green gem quality clear olivine crystals), embedded in a matrix of Fe-Ni metal. The type specimen, weighing 680 kg, was found in the mountains near Krasnojarsk, Siberia, and first documented in 1772 by the German naturalist Peter Pallas after whom pallasites are named. However, it was some decades later before people recognized the extraterrestrial nature of what became known as the Pallas iron.

Pallasites are believed to have come from the core/mantle boundary of differentiated asteroids that were broken apart by impact. However, a new theory proposes that a non-destructive impact between two small planets at the time of formation of the Solar System (more than 4.5 billions years ago) could have formed pallasites. The collision involves two small terrestrial planetesimals (i.e., planets with similar composition to a primitive Earth but with a radius < 1,000 km) in which the the metallic iron-nickel core of the impactor (smaller planetesimal) is injected into the rocky part of the larger body that is made mostly of olivinePallasites have chemical, elemental, and isotopic features that often link them to specific chemical groups of iron meteorites, suggesting that they come from the same parent bodies as these irons1.


Some or all content above used with permission from J. H. Wittke.