Discovery of pressure-induced monoclinic to monoclinic phase transition above 60 GPa in single crystal NaAlSi2O6 jadeite

As one typical aluminum- and sodium-bearing silicate mineral in the crust, the high-pressure behaviors of NaAlSi2O6 jadeite are always of interest for investigation. However, the phase transition of jadeite at lower mantle remains elusive; thus, further static compression experiments and systematic theoretical calculations are highly needed. Here, we report a new monoclinic to monoclinic phase transition of jadeite with a volume collapse of 3.17% at around 68 GPa by in situ Raman experiments and first-principles calculations at high pressures. Such transition leads to the increase of coordination numbers of Si from four- to five-fold coordination, because of Bader charge transfer between SiO and AlO bonds. The physical mechanism behind this transition provides important value to understand the minerals in the lower mantle.