Most small asteroids burn up in Earth's atmosphere and do not reach earth's surface. If any part of an asteroid survives passage through the atmosphere and impact with the Earth it is called a meteorite. There are a few mixed composition meteorites, the stony-iron meteorites. The stony meteorites are divided into two basic groups, the chondrites and the achondrites. They are therefore an indication of relatively unchanged, or primitive materials.
Achondrites have no chondrules.
Chondrites are divided into two main groups, the carbonaceous chondrites and the ordinary chondrites. The presence of these volatile elements indicates that these meteorites have never been heated and that their components have not separated or differentiated. Such meteorites are said to be undifferentiated. Achondrites show even greater signs of heating and differentiation than the ordinary chondrites. The chondrules are recrystallized and sometimes the whole meteorite looks like an igneous rock in Earth, indicating that the rock has been completely or partially melted in its history.