One of two main classes of Meteorite composed of roughly equal amounts by weight of silicate minerals and Ni-Fe metal. The stony-irons consist of two groups: mesosiderites and pallasites. However, there is gradual shading into metal-rich stony meteorites such as the lodranites (once considered stony-irons) and silicate-rich iron meteorites. Stony-iron meteorites are less abundant than their, the other being mesosiderites. Pallasites are igneous in nature and characterized by crystals of Group of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More, sometimes peridot (green gem quality clear olivine crystals), embedded in a Fine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More of Fe-Ni Element that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More. 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 olivine. Pallasites 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.