mesosiderite

Mesosiderite is a class of stony-iron meteorites composed of roughly equal parts metal and silicate material. It belongs to the stony-iron group, distinct from pallasites, which feature olivine crystals in a metallic matrix, and from pure iron meteorites.

Texture and composition: The rock typically shows a brecciated texture in which clasts of silicate rock (predominantly pyroxene and plagioclase, with lesser olivine) are embedded in a metallic matrix of nickel-iron minerals such as kamacite and taenite, often with troilite and minor sulfides. The metal-to-silicate ratio commonly hovers near 1:1, though it varies among specimens.

Origin and formation: Mesosiderites are interpreted as products of collisions on a differentiated asteroid. In such events, silicate crustal material and metallic core melt were mixed and re-accreted, then fractured to yield breccias. Shock metamorphism indicates a complex thermal history with multiple impact events. Radiometric ages place the components in the early solar system, near 4.5 billion years ago.

Name and discovery: The term mesosiderite derives from Greek elements meaning "middle iron," reflecting its intermediate composition between silicate-rich meteorites and irons. The meteorite was identified as a distinct group in the 19th or early 20th century and has since been found in multiple regions, including dry deserts and Antarctica.

Significance: Mesosiderites provide insights into early planetary differentiation, core–mantle mixing, and impact processes in the early solar system; they are studied for isotopic composition and mineral chemistry to understand solar system evolution.