NORTHWEST AFRICA 6928

Diogenite
Norite
standby for nwa 6928 photo
Purchased May 2011
no coordinates recorded

A single stone weighing 223 g was purchased by G. Fujihara from a Moroccan dealer. A sample was submitted for analysis and classification to the University of Washington at Seattle (A. Irving). While NWA 6928 was initially considered to be an unusual basaltic eucrite, chemical analyses revealed that it was a rare noritic diogenite consisting of 80 vol% orthopyroxene (Fs33.4–34.1) and 19 vol% interstitial anorthitic plagioclase, along with accessory (<5 vol%) Ti–Al-bearing chromite, troilite, and merrillite (Irving et al., 2014). New terminology has been proposed in a revision to the diogenite classification scheme utilizing an IUGS-based system (Beck and McSween, 2010; Wittke et al., 2011).

Northwest Africa 6928 has a coarse-grained, cumulus texture and is considered to have crystallized from an ancient, relatively ferroan magma source, possibly a global magma ocean. It exhibits localized shock features including undulose extinction and cataclasis. A number of noritic and feldspathic diogenites have been recognized and described among the more recent meteorite recoveries from the dense concentration area of Northwest Africa, including NWA 8000, 8367, 8744, 10268, and 10388 (Irving et al., 2014, 2016).

The close compositional similarites that exist between the noritic diogenites and mesosiderites suggests that a genetic link might exist (Irving et al., 2016). If that is true, these diogenites probably derive from a parent asteroid distinct from 4 Vesta. The photo of NWA 6928 shown above is a 3.03 g slice expertly prepared by Montana Meteorite Laboratory. The top photo below is the reverse side of the 3.03 g slice, and the bottom photo shows the main mass prior to cutting.

standby for nwa 6928 photo

standby for nwa 6928 photo
Photo courtesy of Big Kahuna Meteorites