The reaction between spodumene (Li₂O • A1₂O₂ • 4SiO₂) and tachyhydrite (CaCl₂ 2MgCl₂ • 12H₂O) at temperatures above 1270 K, when the spodumene has transformed from the unreactive α-form to the β-form, was studied varying the reaction temperature and the relative proportions of the two minerals in the reaction mixtures. Mass balances as well as X-ray diffraction to identify the reaction products indicate that the reactions that occur are 1. a decomposition of the tachyhydrite, losing at first some of its water of crystallization, followed by MgCl₂ hydrolyzing to MgO; 2. a transformation of the α-spodumene into β-spodumene; and 3. a reaction between the β-spodumene, MgO produced from tachyhydrite, and CaCl₂ of the tachyhydrite according to the equation: Li₂O • A1₂O₃ • 4SiO₂ + CaCl₂ + 8MgO = 2LiCl + CaO • MgO • SiO₂ + 3SiO₂ • 2MgO + A1₂O₃ • MgO. X-ray diffraction confirmed the presence of all the phases in the products except the phase containing alumina. Considerations of the quaternary phase diagram Al₂0₃-SiO₂-MgO-CaO show that the phases indicated as reaction products are the ones expected under equilibrium conditions at the reaction temperature. Calculated standard free energy change (△G°) of the suggested reaction is −211926 Joules at 1423 K, indicating that under standard conditions the reaction is possible.