Kaidun is a meteorite that fell on 3 December 1980 on a Soviet military base near what is now Al-Khuraybah in Yemen. A fireball was observed travelling from the northwest to the southeast, and a single stone weighing about 2 kilograms (4.4 lb) was recovered from a small impact pit.
It contains a uniquely wide variety of minerals, causing some confusion as to its origin. It is largely made up of carbonaceous chondrite material of type CR2, but it is known to contain fragments of other types, such as C1, CM1, and C3. Of the nearly 60 minerals found within the meteorite, several have not been found elsewhere in nature, such as florenskyite, which has the chemical formula: FeTiP.
In March 2004 it was suggested that the meteorite originated from the Martian moon Phobos. The reason Phobos has been suggested is the existence of two extremely rare alkaline-rich clasts visible in the meteorite, each of which entered the rock at different times. This suggests that the parent body would have been near a source of an alkaline-rich rock, which is in particular a product of deep differentiation. This points to Mars and one of its moons, and Phobos is more likely than Deimos because it is closer to Mars. However, mineralogical and noble gas work do not tie the lithic fragments to Mars, as has been done with other proven Martian meteorites, and this hypothesized link is tenable at best.
^Ivanov, Andrei V.; Ulyanov, A. A.; Skripnic, A. Y.; Konokona, N. N. (March 1984). "The Kaidun Polymict Carbonaceous Breccia: the Mixture of Incompatible Types of Meteorites". Lunar and Planetary Science (Astrophysics Data System) 15: 393–394. Bibcode:1984LPI....15..393I.