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nakhlite





One of the types of so-called SNC meteorites believed to have come from Mars (see Mars, meteorites from); nakhlites probably formed as lava flows with unusual compositions. They are named for the first member of the group to be found, which fell in pieces in El Nakhla, Egypt, in 1911; local legend has it that one of the fragments hit and killed a dog, though this story may be apocryphal (see Nakhla meteorite for details).

The nakhlites consist mainly of green augite crystals with some olivine in a very fine-grained blend of plagioclase, feldspar, pyroxenes, iron-titanium oxides, sulfides, and phosphates. Most intriguingly, there are traces of pre-terrestrial aqueous alteration products in the form of hydrated minerals, including clay minerals and carbonates. Some researchers think that the presence of these hydrated minerals in the nakhlites, in addition to concentrations of water-soluble ions such as those of chlorine, potassium, sodium, and calcium, suggests that they were once in an environment in which liquid seawater was present for some time, perhaps under an ancient Martian ocean. A problem with this idea is the comparatively young age of the nakhlites: they seem to have crystallized only 1.3 to 1.4 billion years ago and to have been altered by water a mere 700 million years ago, long after Mars supposedly lost its ancient lakes, rivers, and seas.


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   • MARS TOPICS
   • METEORS AND METEORITES
   • ASTROBIOLOGY