Stony Irons

Pallasites

These stony iron meteorites are composed of silicates, mainly large grains of olivine, iron-nickel and troilite, iron sulphide, in fairly equal proportions. The pallasites are subdivided into three subgroups, according to their mineralogy, their chemical and isotopic composition. The olivine-metal association of these rocks suggests that they either originated from the core-mantle boudary of a differentiated parent body (olivine being a typical mantle mineral), or that they formed by collision between a planetary core and some mantle debris.

 

Mesosiderites

These meteorites are breccias also composed of silicates and iron-nickel in similar proportions, as well as troilite. The silicate material is composed of fine-grained matrix and coarse-grained clasts. They are also subdivided into three categories, depending on the level of orthopyroxene present. Unlike the pallasites, they are an assemblage of material from both a crust and a core, presumably involving impact formation.