Xenolith
A xenolith is a fragment of foreign rock enclosed in a different meteorite.
A xenolith, from the Greek for 'foreign stone', is a fragment of rock that clearly comes from a different source from its host. In meteorites, the term usually refers to clasts of another meteorite type embedded in a breccia.
Examples are surprisingly common in regolith breccias, the rubble from asteroid surfaces. Fragments of carbonaceous chondrite, especially CM-like material, have been found in howardites, in ordinary chondrites and in ureilites. The Kaidun meteorite, which fell in Yemen in 1980, contains an astonishing variety of fragments, including enstatite and carbonaceous types side by side. Almahata Sitta, which fell in Sudan in 2008, was a ureilite-dominated asteroid carrying many other types.
Xenoliths show that material moved between asteroids. Small, slow impacts can add fragments of one body to the surface of another, much like dust collecting on a doorstep. Studying them helps map which kinds of asteroid were around in the early Solar System.
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