Unique Spinel-rich Lithology in Lunar Meteorite Alha81005: Origin and Possible Connection to M Observations of the Farside Highlands

Introduction: The discovery of spinel rich rock on the Earth’s Moon, detected by the M near-IR mapping spectrometer on the Chandrayaan-1 spacecraft [1] is among the most intriguing discoveries in a time filled with lunar revelations (e.g., [2]). The M spectrometer discerned several areas on the rim of the far-side Moscoviense basin which had near-IR reflectance spectra characteristic of abundant (Mg,Fe)Al2O4 spinel, with less than 5% mafic silicate minerals (e.g. olivine, pyroxene). Pieters et al. [1] suggested that these outcrops represent a previously unknown lunar rock type, spinel anorthosite, which might be an important component of the lunar crust. However, the origin(s) and formation mechanism(s) of such spinelrich rocks still remain unclear. In addition no such material has previously been described from lunar rocks, either in returned samples or in meteorites. In this study, we describe a fragment of rock containing ~30% Mg-Al spinel from the lunar meteorite ALHA 81005 (Fig. 1).