Abstract
(Mg1-x, Fex) SiO3 majorites with starting composition of X=0. 2 synthesized at 20 GPa and ∼2000-2200°C, and natural majorite in the shocked Tenham meteorite were examined by analytical electron microscopy. The diffraction patterns of synthetic majorites in all the recovered specimens showed a tetragonal symmetry and {101} twins. Tweed structures were also observed in the specimens quenched only from temperatures ≥ 2200°C. On the other hand, natural cubic majorite shows neither tweed structure nor twinning. These contrasting observations suggest that {101} twin lamellae were formed by the cubic-tetragonal phase transition during quenching. Cubic (Ia 3 d) majorite seems to have a wide stability field at high pressures and high temperatures.
