Enstatite chondrites contain the most refractory elements and are believed to have formed in the inner solar system. Ordinary chondrites, being the most common type containing both volatile and oxidized elements, are thought to have formed in the inner asteroid belt. Carbonaceous chondrites, which have the highest proportions of volatile elements and are the most oxidized, are thought to have originated in even greater solar distances. Each of these classes can be further subdivided into smaller groups with distinct properties. Other meteorite types which have been geologically processed are achondrites, irons and pallasites.
Achondrites are also stony meteorites, but they are considered differentiated or reprocessed matter.
Pallasites are stony iron meteorites composed of olivine enclosed in metal. Iron meteorites are classified into thirteen major groups and consist primarily of iron-nickel alloys with minor amounts of carbon, sulfur, and phosphorus. These meteorites formed when molten metal segregated from less dense silicate material and cooled, showing another type of melting behavior within meteorite parent bodies. Thus, meteoritescontain evidence of changes that occurred on the parent bodies from which they were removed or broken off, presumably by impacts, to be placed in the first of many revolutions. The motion of meteoroids can be severely perturbed by the gravitational fields of major planets.