NORTHWEST AFRICA 4020


L/LL3
standby for nwa 4020 photo
Found 2005
no coordinates recorded

Ten pieces constituting a single stone with a combined weight of 209.4 g was found by an anonymous hunter and later sold in Morocco to collector H. Strufe. A portion was submitted for analysis to the Museum für Naturkunde, Berlin, Germany (A. Greshake and M. Kurz). Northwest Africa 4020 was classified as an L/LL3, a transitional unequilibrated ordinary chondrite. This meteorite has been weakly to moderately shocked (S3/4), and has experienced heavy terrestrial oxidation (W3).

It was demonstrated by Szurgot (2016) that the mean atomic weight (Amean) of meteorites can be used to resolve the OC groups, including the intermediate groups L/LL and H/L. Amean values can also be predicted through various equations based on other parameters such as atomic Fe/Si ratio, grain density, and magnetic susceptibility, and these Amean values all consistently resolve these groups into the ordered sequence LL < L/LL < L < H/L < H. Furthermore, it was demonstrated that Amean values are lower for unequilibrated type 3 samples than for equilibrated samples within each OC group due to the presence of water; Amean values for petrologic types 4–6 are indistinguishable within each group.

standby for amean diagram
Diagram credit: M. Szurgot, 47th LPSC, #2180 (2016)
Amean based on chemical composition (Eq. 1), Fe/Si atomic ratio (Eq. 2), and grain density (Eq. 3)

A brief review of the evidence supporting a separate L/LL parent body can be found on the Inman page. The specimen of NWA 4020 shown above is a 1.4 g partial end section.