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Primitive achondrites mark a borderline between primordial and differentiated matter as they retained the primitive chemical and isotopic patterns of their chondritic precursors while having changed their overall texture through partial melting and moderate igneous processing. Their respective parent bodies were probably just too small to amass the necessary amount of Al26, the radioctive element that has been responsible for the initial heating, melting, and processing of all asteroids, planetisemals, and planets in our solar system. They also lacked the mass to retain the initial heat, and cooled very quickly, leaving the primitive achondrites as a witness for an uncomplete differentiation.
Larger bodies with enough mass completed the process of heating, melting, and remelting to various degrees, leading to the separation of the more heavy elements, such as nickel and iron, to form a core, and the lighter elements, and minerals, mostly silicates, to form an outer mantel and crust. The terrestrial planets, such as Mercury, Venus, and Mars, are the perfect examples of a completed differentiation process, but also our own Moon, and a few asteroids belong to the group of the differentiated parent bodies. Contempory research has proved that some classes of evolved achondrites actually represent the outer crust, and the mantle of the planet Mars, the Moon, or the asteroid Vesta, one of the largest asteroids in our solar system.
However, some worlds had to be destroyed to reveal their initial degree of differentiation. Samples of such worlds, disrupted by violent impact events, and cosmic collisions, are the siderites, subdivided into the stony-iron meteorites, and iron meteorites. While stony-iron meteorites, such as the most intriguing pallasites, are thought to represent the core-mantle boundary where silicates and metal mixed in intriguing patterns, some iron meteorites are thought to actually represent core samples of differentiated asteroids that had been disrupted in the early days of the formation of our solar system. Have a look at the respective pages to learn more about the classes, clans, and groups of differentiated meteorites.