Lunar Olivine Gabbros

We have a few thin sections of lunar olivine gabbros in our collection. They are all of the NWA 773 clan. Randy Korotev says: The NWA 773 clan is one of the most unusual of lunar meteorites. It is unlike any rock in the Apollo collection. It contains at least 5 different igneous lithologies. The total mass of these stones is 11.87 kg.

Here we will focus on the olivine gabbro.

More from Randy Korotev’s NWA 773 clan pages ( Lunar Meteorite: Northwest Africa 773 clan | Some Meteorite Information | Washington University in St. Louis )

The modal mineralogy of NWA 773 olivine gabbro in percent (in the MetBull) is olivine 55, augite 5, pigeonite 24, hypersthene minor, plagioclase 15, alkali feldspar minor, ilmenite, chromite, alkali feldspar, phosphates, troilite and FeNi metal <1.

The olivine gabbro is coarse grained and the thin sections are small, so the modal mineral proportions obtained from different sections do not agree well. Because augite and pigeonite, both clinopyroxenes, dominate over orthopyroxene (hypersthene), which is minor, the rock is a gabbro, not a norite. Specifically, it is an olivine gabbro because olivine exceeds 10%. If plagioclase is actually <10%, then it is a peridotite.

We’ll look at our examples in the reverse order of their classification:

NWA 6950 Lunar (gabbro)
NWA 2977 Lunar (gabbro)
NWA 2727 Lunar (bas/gab brec) formerly Lunar (mare basalt/gabbro breccia)
NWA 773 Lunar (gabbro) formerly Lunar (ol norite), Lunar (cumulate olivine norite with regolith breccia) and Lunar (norite)