NORTHWEST AFRICA 5206


LL3.05
standby for nwa 5206 photo
Purchased October 2007
no coordinates recorded

A single weathered (W3) meteorite weighing 1,276 g was found in Algeria and sold to a meteorite dealer in Erfoud, Morocco. Analysis and classification of the stone was conducted at Northern Arizona University (T. Bunch and J. Wittke), and it was determined that NWA 5206 is a very weakly shocked (S2), terrestrially weathered (W3), highly unequilibrated LL3.05 (or possibly lower) chondrite.

Chondrules of both type-I and type-II compositions are present in a ratio of 3:1, respectively. Chondrule textures span a broad range; porphyritic types predominate, while the remainder comprises granular, radial, cryptocrystalline, barred, and a number of unique types, some with thick mantles. In addition to the primitive compositional heterogeneity of this chondrite, other petrographic and chemical characteristics, such as the alkali-poor glassy chondrule mesostasis and the Cr distribution in ferroan olivine, has led investigators to conclude that NWA 5206 is highly unequilibrated with a subtype <3.1. A more extensive review of the most recent techniques used to discriminate among the lowest petrologic types can be found on the NWA 1756 page.

Utilizing Al–Mg chronometry for a broad sampling of unequilibrated ordinary chondrites, Pape et al. (2019) ascertained that five type-II chondrules from NWA 5206 provide 26Al–26Mg isochron ages of ~1.97 to ~2.64 m.y. after formation of CAIs. The total age range for the entire sample set is ~1.76 to ~2.92 m.y. after CAIs, attesting to chondrule formation occurring over an interval of ~1.2 m.y., or ~1.5 m.y. when including the oldest known chondrules.

standby for nwa 5206 chondrule age diagram
Diagram credit: Pape et al., GCA, vol. 244, p. 429 (2019)
'Time and duration of chondrule formation: Constraints from 26Al-26Mg ages of individual chondrules'
(https://doi.org/10.1016/j.gca.2018.10.017)

Very few ordinary chondrites have been classified as petrologic subtype 3.05 or lower, and NWA 5206 is the only LL chondrite designated as such. A comprehensive pictorial review of NWA 5206 can be found on the Meteorites Australia page showing examples of the many chondrule types and exotic components such as metallic chondrules armored with troilite, xenolithic chondrule fields, and dark inclusions. The specimen of NWA 5206 shown above is a 7.47 g partial slice. The photo below shows a view of the main mass, courtesy of M. Cimala.

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Photo courtesy of Marcin Cimala—Polish Meteorite Laboratory