Ureilites do not seem to have anything in common with the other acondrites. They are formed by olivine and orthopyroxene, and are characterized by the fact that they contain carbon in the form of microscopic diamonds. This means that they must be formed in extreme pressure and high temperature and then large asteroid collisions are the best explanation. The name comes from Russian Novy Urey where a meteorite of this type fell 4 sept. 1886