The phase diagrams of the LiAlSi2O6-MgSiO3 and LiAlSi2O6-CaMgSi2O6 isopleths were experimentally investigated at 1atm using the quenching method and differential scanning calorimetry and the phases produced were characterized with the help of X-ray diffraction and electron probe microanalysis. With the help of thermodynamic optimization, the phase diagrams of both systems were more accurately reported. No detectable solubility of Li2O in diopside and enstatite was found. However, both systems are not simple binary eutectic systems because their phase equilibria are somewhat complex due to the presence of some -spodumene solid solution. In the -spodumene solid solution, no notable solubility of MgO and CaO was detected; evidence of significant solubility of SiO2 was confirmed.