Mesosiderites

Mesosiderites are a class of stony-iron meteorites that exhibit a distinctive brecciated texture in which metallic nickel–iron is interlaced with silicate-rich clasts. They typically contain substantial metal alongside a silicate component, with textures that show silicate fragments embedded in a metal-rich matrix. The bulk composition often places them between irons and stony meteorites, and individual specimens can vary in the precise balance of metal and silicate.

Petrology and mineralogy

The metal in mesosiderites is predominantly kamacite and taenite, while the silicate portion includes orthopyroxene, pigeonite, olivine, and plagioclase, with minor quartz in some samples. Silicate clasts range in size from grains to lithic fragments and can resemble crustal or igneous rocks. Troilite and other sulfides are commonly present, and glassy inclusions or impact-melt pockets may occur within the matrix. The overall texture reflects multiple impact events that mixed metal and silicate materials into a brecciated assemblage.

Formation and origin

Mesosiderites are widely interpreted as products of early solar-system differentiation and collisional processing. A leading scenario posits that metal from a differentiated asteroid core was mixed with silicate mantle or crust material during large impacts, producing metal-rich breccias containing diverse silicate clasts. This differs from pallasites, which display a clearer metal–silicate interface, and records the early collisional history and internal structure of their parent body.

Classification and occurrence

They belong to the stony-iron meteorite group, alongside pallasites. Mesosiderites are less common than pallasites and have been recovered worldwide, with several meteorite finds from Antarctica contributing to their study. They provide insights into planetary differentiation and the early evolution of meteoritic parent bodies.

See also: stony-iron meteorites, pallasites, meteorite formation.