Mineralogy of Antarctic lunar meteorites and differentiated products of the lunar crust

The mineralogy of clasts containing pyroxenes and glassy matrices of lunar meteorites, Yamato-791197 (Y-791197) and Allan Hills A81005 (ALHA81005) has been studied by an electron microprobe and an analytical transmission electron microscope (ATEM). A rare brown pyroxene-rich clast (HPF) consists of hedenbergite, Ca-poor iron-rich pyroxene, plagioclase, fayalite, silica and ilmenite. This exotic component may be a differentiated product of the lunar crust or an iron-rich portion of a basalt. The evolutionary trend of Y-791197 from spinel troctolite to anorthosite in the An content vs. Mg/(Mg+Fe) diagram is similar to that of ALHA81005 and is located between the Mg-rich suite of rocks and ferroan anorthosite. It is difficult to prove that this trend represents a single differentiation and that the HPF clast is on the extension of this trend, because the data appear to define a trend of extremely steep slope. The glass in the matrix of ALHA81005 is devitrified on the TEM scale.