A stone meteorite weighing 605 g was purchased by M. Graul and a sample was sent for analysis and classification to the Institut für Planetologie in Münster, Germany (K. Metzler). Analyses of NWA 13400 resulted in a classification of C3-ungrouped. In a subsequent study, the percentage mean deviation (PMD) of olivine fayalite values was used as an indicator of the degree of equilibration (Metzler et al., 2021). Northwest Africa 13400 has a PMD value between 5% and 10% and is therefore designated petrologic subtype 3.9.
This carbonaceous chondrite has a low matrix abundance of 17 vol% with metal-bearing chondrules (up to 2.8 mm; ave. 0.48 mm), chondrule fragments, and CAIs (up to 3.8 mm). An O-isotopic analysis was conducted at the Open University (R. Greenwood), and the meteorite has an oxygen three-isotope value that plots within the CVCK field (see diagram below). After further in-depth analyses of NWA 13400 as well as Coolidge (C4), Loongana 001 (C4), Los Vientos 051 (C3.9), and NWA 033 (C4), Metzler et al. (2021) assigned these five meteorites to a new CL group which derives its name from Loongana 001.
Diagram credit: Metzler et al., GCA, vol. 304, p. 22 (2021)
'The Loongana (CL) group of carbonaceous chondrites'
References have previously been made by some investigators to other potential members of the CL group, including HaH 073, Sahara 00182, and NWA 779. All of these meteorites were subsequently investigated by Metzler et al. (2021) and extensively compared to the newly established parameters which define the CL group. They concluded that differences are apparent in these characteristics for each of the meteorites, some of which are very significant differences, and they can all be excluded as members of the CL group; however, HaH 073 could be distantly related in a way that is yet to be determined (see the Coolidge page for further information about this group).
Northwest Africa 13400 is shocked to stage S2 and is weathered to a grade of W2/3. The specimen of NWA 13400 shown above is a 0.847 g partial slice. The photos below show the reverse side and an edge-on view of this specimen, courtesy of Mirko Graul.