In particular, the MgO-GeO2 system exhibits a very simi- lar phase diagram as its natural analogue, the upper mantle (MgO-(FeO)-SiO2 system; Figure 2) [53,54]. Thanks to very similar properties [55–57], Mg2GeO4 has been used in numerous studies as an analogue of (Mg,Fe)2SiO4 ...