Synonyms: bustites, enstatite achondrites


General: The meteorites of this group are named for Aubres, a small achondrite that fell near Nyons, France, in 1836. Being primarily composed of the orthopyroxene enstatite, aubrites are often called enstatite achondrites. However, they are evolved rocks of igneous origin, and thus the aubrites are not to be confused with primitive enstatite achondrites, such as NWA 1235, Zaklodzie, or our own unique find, Itqiy.


Description: All aubrites exhibit a typical light-colored, brownish fusion crust, and a more or less white and brittle interior. They are magmatic rocks with a coarse-grained to pegmatitic texture, and most aubrites are heavily brecciated, some of them containing xenolithic clasts of chondritic composition (e.g., ALH 78113, and Cumberland Falls).


Mineralogy: Aubrites are primarily composed of large white crystals of the Fe-poor, Mg-rich orthopyroxene, enstatite. As minor phases they contain olivine, nickel-iron metal, troilite, and several exotic accessory minerals, indicating a magmatic formation under extremely reducing conditions.


Formation history: The aubrite magmas probably formed from an enstatite chondrite source, suggesting a close relationship to the E chondrites. The severe brecciation of most aubrites attests to a violent history for their parent body, which resulted in the xenolithic inclusions. As has been stated above, some aubrites contain chondritic xenoliths of forsteritic composition, indicating that the aubrite parent body collided with an asteroid of "F-chondritic" composition short after its formation.


Origin: Asteroidal. Comparisons of aubrite spectra to the spectra of asteroids have revealed striking similarities between the aubrite group and the main belt asteroid 44 Nysa, as well as to other members of the Hungaria family. One smaller member of this asteroid family, the unnamed asteroid 3103, exhibits a near-Earth orbit, and is suspected of being the actual parent body of the aubrites.


Members: If we exclude all probable pairings, only 15 different aubrites are known. Most of them are witnessed falls, such as Bustee, Pena Blanca Springs, Mayo Belwa, and the famous Norton County, and only a few are finds from Antarctica. No aubrite has been recovered from the deserts of Africa or Asia thus far, maybe due to the brittle nature of these rare achondrites, or due to the fact that aubrites don't exhibit a black fusion crust, making them hard to spot in a light-colored desert environment.


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