NORTHWEST AFRICA 13400

CL3.9

Purchased December 2016
no coordinates recorded

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 CV–CK 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'
(https://doi.org/10.1016/j.gca.2021.04.007)

Wölfer et al. (2026) presented both new and literature Ti, Cr, and Mo isotope data for a large variety of meteorites and planetary bodies. The isotopic data presented for the bulk CL group and a representative chondrite NWA 13400 are consistent within error. Northwest Africa 13400 plots in a unique space on a ε⁹⁴Mo vs. ε⁹⁵Mo coupled diagram as demonstrated in their Figure 3 shown below.

Ti, Cr, and Mo Isotopic Data for NWA 13400 and Bulk CL
(Wölfer et al., 2026; Metzler et al., 2021)
ε⁴⁶Ti ε⁴⁸Ti ε⁵⁰Ti ε⁵³Cr ε⁵⁴Cr ε⁹⁴Mo ε⁹⁵Mo

NWA 13400   0.53 (±0.08)
0.53 (±0.06)   –0.05 (±0.04)
–0.05 (±0.03)   2.73 (±0.11)
2.60 (±0.07) 0.14 (±0.13) 0.70 (±0.13) 1.14 (±0.10) 0.99 (±0.06)

CL   0.49 (±0.05)
0.48 (±0.06) –0.03 (±0.08)   2.63 (±0.14)
2.60 (±0.22)   0.07 (±0.05)
0.07 (±0.05)   0.70 (±0.08)
*0.72 (±0.08) 1.14 (±0.10)

ε⁹⁴Mo vs. ε⁹⁵Mo Plot for NWA 13400
open blue square = NWA 13400 as indicated

click on image for a magnified view

Diagrams credit: Wölfer et al., GCA, vol. 430, pp. 31–48, fig. 3 (2026, open access link)
'Origin of nucleosynthetic isotope variability in the NC reservoir: evidence from Ti, Cr, and Mo isotopes'
(https://doi.org/10.1016/j.gca.2026.08.021)

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).

The small concentration of trapped 20Ne and other noble gases detected in CL3.9 NWA 13400 by Alosius et al. (2023 #6247), in comparison to the lack of noble gases detected in the CL4 members of the group, is consistent with its slightly lower degree of thermal metamorphism. 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, while the photos below show the reverse side and an edge-on view of this specimen, courtesy of Mirko Graul.

Photos courtesy of Mirko Graul