Solid‐state Equilibrium Relations in the System MgO‐Al ₂ O ₃ ‐SiO ₂ ‐ZrO ₂

Using techniques developed by Goldschmidt and lately utilized by Foster, solid‐state equilibria were studied in the system MgO‐Al 2 O 3 ‐SiO 2 ZrO 2 . The ternary systems MgO‐Al 2 OrSiO 2 and MgO‐SiO 2 ‐ZrO 2 are the only faces of this four‐phase system that have beep studied extensively. Compositions in each of the four faces were heated to temperatures below their fusion point and, after they had been cooled, they were examined by X rays to identify the phases present. After solid‐state equilibria had been established or verified in the four faces of the system, quaternary compositions were studied to determine the Alkemade tetrahedra.