中国科学院地球化学研究所机构知识库

Forty-five years after the Apollo and Luna missions, Chinas Change-5 (CE-5) mission collected 1.73 kg of new lunar materials from one of the youngest basalt units on the Moon. The CE-5 lunar samples provide opportunities to address some key scientific questions related to the Moon, including the discovery of high-pressure silica polymorphs (seifertite and stishovite) and a new lunar mineral, changesite-(Y). Seifertite was found to be coexist with stishovite in a silica fragment from CE-5 lunar regolith. This is the first confirmed seifertite in returned lunar samples. Seifertite has two space group symmetries (Pnc2 and Pbcn) and formed from an alpha-cristobalite-like phase during cold compression during a shock event. The aftershock heating process changes some seifertite to stishovite. Thus, this silica fragment records different stages of an impact process, and the peak shock pressure is estimated to be 11 to 40 GPa, which is much lower than the pressure condition for coexistence of seifertite and stishovite on the phase diagram. Changesite-(Y), with ideal formula (Ca8Y)◻Fe~(2+)(PO4)7 (where ◻ denotes a vacancy) is the first new lunar mineral to be discovered in CE-5 regolith samples. This newly identified phosphate mineral is in the form of columnar crystals and was found in CE-5 basalt fragments. It contains high concentrations of Y and rare earth elements (REE), reaching up to 14 wt.% (Y,REE)2O3. The occurrence of changesite-(Y) marks the late-stage fractional crystallization processes of CE-5 basalts combined with silicate liquid immiscibility. These new findings demonstrate the significance of studies on high-pressure minerals in lunar materials and the special nature of lunar magmatic evolution.