Tissintite-II and Other High Pressure/Temperature Minerals in Lunar Meteorite NWA 13967

Lunar meteorites are created when an asteroid impacts the Moon. In such events, the lunar surface, known as regolith, can experience extreme pressures and temperature conditions. Some of this regolith material can be ejected from the Moon and enter interplanetary space where it can be captured by Earth's gravity. Even after falling to Earth, the minerals of lunar meteorites preserve the history and conditions of lunar impact processes. One such mineral that has gained attention recently is tissintite due to its relatively specific temperature and pressure formation conditions. The lunar meteorite NWA 13967 and its mineral assemblage provided an opportunity for comparison to other lunar meteorites (Zhang et al. 2021). Based on its mineralogy and petrography, NWA 13967 likely experienced peak pressures of 18 to 24 GPa and peak temperatures above 2000℃, as indicated by the presence of intergranular melt, vesicles, and corundum. The occurrence of tissintite-II and coesite suggest crystallization during cooling and decompression, while other high pressure minerals likely back-transformed to lower pressure polymorphs.