Ureilites do not seem to have anything in common with the other acondrites. They consist of olivine and orthopyroxene as well as carbon in the form of graphite and microscopic diamonds. There is no full explanation for the formation of the ureilites, but since they contain diamonds formed from graphite, there must have been extreme pressure and temperature present. Then asteroid collisions can be an obvious explanation. But the strange thing is that they have olivine, pyroxene, carbon and volatile gases in them, which means low-temperature formation. The name originates from Russian Novy Urey where a meteorite of this type fell 4 sept. 1886