FIRST IDENTIFICATION OF CALCITE INCLUSION WITHIN THE LUNA-20 LUNAR SAMPLE: A COMBINED CATHODOLUMINESCENCE AND MICRO-RAMAN STUDY

Investigations of the lunar material revealed that the mineral composition of lunar rocks seems to be much simpler than that of terrestrial rocks. Plagioclase is the most abundant mineral of the highland rocks (enriched in Ca and Al), whereas pyroxene, plagioclase and ilmenite dominate the mare basalts (pyroxene together with plagioclase 75-90%). Furthermore, the lack of an atmosphere and water result in a complete lack of surface minerals such as clay minerals or carbonates. In contrast to these findings, the present study indicates the existence of minor carbonate phase in a rock fragment of a Luna 20 sample. The landing site of Luna 20 was in the highland region between Mare Fecunditatis and Mare Crisium (3°32'N and 56°33'E). The loose-grained, light grey regolith consists of about 50% degraded bedrock and thus is mature soil. The lithic fragments are mainly composed of anorthositic norite and troctolite with Ca-rich plagioclase, pyroxene, olivine, and only minor basaltic constituents. In one of the rock fragments of Luna 20 regolith with mainly quartz and alkali feldspar, an accessory component was detected due to its bright CL. Because of the typical bright orange luminescence emission it was firstly concluded that it might be a carbonate phase. SEM-CL-EDX analyses showed only CaO and elevated carbon content. The CL spectrum shows a blue emission and the typical broad band at ca. 615-620 nm, which can be related to the activation by Mn²⁺. The micro-Raman vibrational modes centered at 297 (vw/very weak), 713 (m/medium) and 1090 (vs/very strong) cm^-1 associated with a SiO₂-phase, which is dominated by strong

peak at 464 cm^-1. Consequently, these cathodoluminescence and micro-Raman spectral features above indicate the occurrence of calcite as an inclusion within SiO₂-matrix of Luna-20 sample. According to this observation, there are two possible scenarios for the formation of calcite on the Moon: (1) meteoritic and (2) hypervelocity impact origin. Calcium elements from anorthite on lunar highland should be mixed with elements from carbonaceous chondrites (containing Ca-Al inclusions) or comets. When a large body strikes Earth, impact debris can be accelerated to orbital speed and achieve Earth orbit indicating to sweep up some of the terrestrial debris by Moon.