Petrology of fine-grained rock fragments and petrologic implications of single crystals from the Luna 20 soil

Abstract

Only fine-grained rocks are present in the Luna 20 samples, and coarser grained rocks are represented by fragments of single crystals. A petrologic study has been made of 47 fine-grained crystalline rocks, microbreccias, and glassy aggregates. In addition, a total of 33 single crystals of pyroxene, plagioclase, olivine and spinel, in the size range 125 to 500 μ, have been examined using electron microprobe and single crystal X-ray diffraction techniques. The most abundant fine-grained crystalline rocks in the samples we have examined are recrystallized anorthositic norite and anorthositic troctolite. Gabbroic rocks, anorthosite, and KREEP basalt are present but not common. Most of the single crystals of pyroxene and plagioclase could have been derived from coarser grained noritic, troctolitic and anorthositic rocks. However, three of the 14 pyroxene crystals, and 2 of the 5 olivine crystals have Fe (Fe + Mg) contents greater than 0.45 and are believed to have been derived from mare basalts or related rocks. Two relatively sodic crystals of plagioclase were found. One is a crystal zoned at least over the range An 85 to An 63, and the second is a homogeneous crystal of albite (~An 3).