One of two main types of stony-iron meteorite, the other being pallasites. Mesosiderites are a mixture of approximately 50% basaltic, gabbroic and orthopyroxenitic silicates and 50% Ni-Fe metal and sulfides. The name derives from the Greek “mesos” meaning “middle” or “half” and “sideros” for “iron;” hence “half-iron”. The silicates are heavily brecciated igneous rocks, similar to eucrites, diogenites, and clearly came from the crust of an achondritic parent body. The metal in mesosiderites is similar to that of IIIAB irons, and came from the core of a differentiated asteroid, genetically unrelated to the precursor of the eucritic and diogenitic portion. Mesosiderites have no mantle-like material at all. This odd combination of crustal and core material can be explained (though still debated) by a collision of two differentiated asteroids in which the still-liquid core of one asteroid mixed with the solidified crust of the other. This model requires collisional disruption followed by gravitational reassembly of at least one of the asteroids.

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