Almost all chondrites contain chondrules - small, gaseous, spherical inclusions that formed during the solar nebula. Achondrites appear to have been chondritic before being altered by a heating or impact event. These meteorites are much rarer than chondrites and include the HED group from asteroid 4 Vesta and SNCs from the planet Mars. Iron meteorites are thought to be pieces of the shattered cores of differentiated asteroids and contain varying amounts of nickel. Octahedrites containing 6.5 to 13 percent nickel and Ataxites with nickel amounts of 16 to 30 percent.
Iron meteorites are the most common group of meteorites by weight.
Mesosiderites and Pallasites are the two main groups of the stony-iron meteorites. Mesosiderites consist of broken angular fragments of mantle rock and nickel-iron that have been fused together by impacts with another body.