Three conjoint fragments of an unequilibrated chondrite, having a combined weight of 1,805 g, were found in the Sahara Desert and sold to G. Hupé in Erfoud, Morocco. This meteorite was analyzed and classified at Northern Arizona University (J. Wittke and T. Bunch) as an L-type ordinary chondrite.
A new petrologic scheme that is more discriminating at the lowest metamorphic stages, those associated with the highly unequilibrated chondrites (3.03.2), was developed by Grossman (2004), Grossman and A. Brearley (2005), and Grossman (2008). This new classification scheme is based in part on a sensitive analytical technique utilizing the variation in the distribution of Cr in ferroan olivine, and it is virtually unaffected by the processes of terrestrial weathering and aqueous alteration. The petrologic scale of the new decimal system has been extended as follows:
For metamorphic types 3.003.03, chromite contents account for 0.30.5 wt% in the chondrite groups studied. While chromite contents in type 3.053.10 chondrites still reflect the lowest degrees of metamorphism, at a degree of metamorphism equivalent to type 3.15 the chromite abundance has declined to only 0.10.2 wt%. With metamorphic types of at least 3.2, the chromite abundance is mostly less than 0.1 wt%. Northwest Africa 2798 has a measured Cr content in olivine of 0.21 (±0.09) wt%, and with consideration of other parameters, has been assigned to subtype L3.2. It has a shock stage of S2 and a low weathering grade of W1. The specimen of NWA 2798 pictured above is a 6.13 g complete slice.