Aubrites are rare, asteroidal pyroxenites.  About 66 aubrites have been recorded so far.  Pyroxenite is a >90% pyroxene-bearing, ultramafic intrusive igneous rock.  The pyroxene in aubrites is mostly in the form of enstatite (MgSiO3), but there's a little diopside as well.  The most remarkable aspects of aubrite meteorites are their pale to whitish color and their remarkable fragility.


The aubrite shown below is a 2.4 gram fragment of the Bishopville Meteorite, a 13 pound rock which impacted on 25 March 1843 in Bishopville, Lee County, South Carolina, USA.  The Bishopville Aubrite is a fragmental breccia apparently derived from near the surface of its parent body.


Aubrites are dominated by enstatite, but their minor and trace mineralogy typically includes forsterite olivine, plagioclase feldspar, diopside, Fe-Ni metal, Ti-troilite (or Ti-pyrrhotite), schreibersite, alabandite, oldhamite, schšllhornite, etc.  Bishopville has a very high plagioclase feldspar component for an aubrite - 16% of its volume is plagioclase.


Based on CRE (cosmic ray exposure) age determinations of various aubrites, the parent body or bodies (maybe up to 4 separate bodies?) have been subjected to several major impacts or breakup events.  It's suspected that the ~near-Earth orbiting, E-class asteroid named Eger (or some other E-class asteroid, such as Nysa) is the likely source of most aubrite meteorites.  Bishopville has a CRE date of 52 to 57 million years (= how long ago the rock was ejected from its parent body).


Aubrite crystallization ages go back to the beginning of the solar system, as do almost all asteroidal rocks.  Available age information shows that the Bishopville Aubrite is 4.547 to 4.553 billion years old.



Aubrite (2.2 cm across) - fragment of the Bishopville Meteorite.



(More info. on the Bishopville Aubrite)



Synthesized from various sources, principally Floss et al. (1990), Weber & Bischoff (1999), Hutchison (2004), Welten et al. (2004), Shukolyukov & Lugmair (2004), Skala & Drabek (2005), and Miura et al. (2007).



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