Lunar Ferroan Anorthosite
standby for gadamis 003 photo
click on photo for a magnified view

Found 2021
30° 17' 2" N., 11° 0' 18" E.

Initially, three stones weighing together 712 g were found in 2020 near Ghadamis, Libya and purchased by J. Piatek. These three stones were named Ghadamis 002 and classified at the University of New Mexico (C. Agee) as lunar ferroan anorthosite. Two additional paired stones with a combined weight of 1,270 g were found in 2021 and purchased by M. Lyon and C. Zlimen. These two stones were named Ghadamis 003 and also classified at UNM (A. Ross and C. Agee). The recovery of several other paired stones has been reported, including the largest mass weighing 12.66 kg which was classified at UNM (C. Agee) as Ghadamis 004. The Ghadamis 002/003/004/005 meteorite is only the second lunar anorthosite classified after the 265 g unbrecciated Ghadduwah 001, which was found in Awbari, Libya in January 2020 (University of New Mexico, C. Agee; see photos).

The lunar ferroan anorthosites represent Ca- and Al-rich cumulate rocks that formed as a flotation crust above a slowly-cooled magma ocean (Taylor et al., 1991). As described by Paul Warren (2022 #6047), the ferroan anorthosites have high olivine/pyroxene ratios "despite having mg much lower [~ 61–64 mol%] than the ratio at which, among Mg-suite cumulates, the mafic silicates transition from olivine to pyroxene". He recognized that the mineralogy of ferroan anorthosite rocks is inconsistent with a post-crystallization mixture between olivine-free ferroan anorthosite and olivine-bearing Mg-suite material, but instead was uniquely produced within a convecting magma chamber wherein cumulus plagioclase was mixed with shallow-formed (low-temperature) cumulus olivine and more-deeply formed (high-pressure) cumulus pyroxene.

Dating of similar lunar anorthosite rocks was accomplished by using the Sm–Nd isotopic system for the least alterable mafic components (Norman et al., 2003). An early crystallization age of 4.46 (±0.04) b.y., or ~100,000 years after CAIs, was obtained, which is consistent with a late collisional formation scenario for the Moon.

Ferroan anorthosites are the most common rock type identified at the Apollo 16 highland landing site. The MetBull 110 writeup for the Ghadamis 002/003 meteorites states they are composed predominantly of brecciated, cataclastic anorthitic plagioclase (98–99%) along with sparse micron-scale poikilitically enclosed olivine and pyroxene grains (~1-2%). In the diagram below, the ferroan anorthosites are located close to the feldspar major mineral quadrant (Taylor et al., 1991).

Major Mineral Modes for Lunar Rocks
lunar modes
click on photo for a magnified view

Diagram credit: Taylor et al., Lunar Sourcebook, ch. 6: Lunar Rocks, p. 215, (1991 open access link)
Cambridge University Press; Grant H. Heiken, David T. Vaniman, Bevan M. French, eds.

The "Genesis rock" returned by Apollo 15 is a 269 g ferroan anorthosite. The specimen of Ghadamis 003 pictured above is a 4.48 g slice. The Facebook Live video below shows Ashley Rose Humphries displaying the main mass at the 2022 Denver Gem and Mineral Show.

For additional information on dating lunar anorthosites, read the PSRD article by Marc Norman: 'The Oldest Moon Rocks', April 21, 2004.