A single stone weighing 354 g was purchased by F. Kuntz from in Morocco. Sample were submitted for analysis and classification to the Northern Arizona University (T. Bunch and J. Wittke). Previously, NWA 5312 was determined to be consistent with membership in the newly characterized olivine diogenite group, but in accordance with the new terminology proposed in a revision to the diogenite classification scheme, utilizing an IUGS-based system, NWA 5312 is now considered to represent the olivineorthopyroxenite subgroup of diogenites (Beck and McSween, 2010; Wittke et al., 2011).
Northwest Africa 5312 is composed of 46 vol% orthopyroxene, 24 vol% olivine, and 18 vol% troilite, along with lesser amounts of merrillite, chromite, and taenite (Irving et al., 2009). Oxygen isotopic ratios determined for NWA 5312 overlap those of other HED members (D. Rumble III, Carnegie Institution). Other members of this rare diogenite group include GRA 98108, ALHA77256, LEW 88679, and NWA 5405.
For more details on the formation of diogenites visit the Johnstown page. The photo of NWA 5312 shown above and below is a 6.95 g partial slice.