Chondrites are, by far, the most abundant type of stony meteorite. Less common, comprising only a few percent of all meteorites, are achondrites. These are also stony meteorites composed primarily of silicates, but these meteorites have experienced familiar geologic processes of melting and differentiation - although these happened long ago. Most achondrites formed on asteroids during the birth of the Solar System, but a small number formed on Mars and the Moon. Stony-iron meteorites form in places where metal and silicate are mixed.
Pallasites probably form when the olivine-rich mantle of an asteroid mixes with the metallic core.
Mesosiderites are mixtures of iron-nickel metal and basalt and probably formed by the collision of two asteroids. Iron Meteorites Iron meteorites are really composed of iron and nickel and are extremely dense. They are pieces of the cores of asteroids. Iron meteorites are the samples of the cores of ancient worlds. One of the most distinguishing features of meteorites is the presence of the Widmanstatten pattern - the distinctive series of bands in geometric patterns.