Majorite Garnet

Majorite garnet or majorite ( English majoritic garnet , majorite ) is a mineral of the garnet group with the chemical formula Mg ₃ (MgSi) (SiO ₄ ) ₃ . Opened in 1970. Named after Alan Major, who worked with E. Ringwood on the synthesis of high- barren garnets . ^[one]

It differs from other garnets in that all silicon is located in it both in oxygen tetrahedrons and in octahedrons . A detailed study of Na-majorite crystals using single - crystal X-ray diffraction made it possible to establish the tetragonal syngony of this phase with the space group I41 / acd. ^{[2] [3]}

The formation of major garnet is associated with high-pressure dissolution of the major (MgSiO ₃ ) component in garnet , which occurs under sublitospheric conditions (lower part of the upper mantle and transition zone ). ^[4] Moreover, the conversion of orthopyroxene begins already at a depth of 410 km, and clinopyroxene is transformed into major garnet only at the “520 km” boundary. Below the global “670 km” border, the major is replaced by perovskite-like phases, which account for about 80% of the lower mantle volume.

During the ascent of rocks to the upper horizons of the Earth , major decomposition structures of pyroxene often arise in majorite, reflecting their decompression decomposition. ^[5] The presence of such oriented intergrowths in garnets of metamorphic complexes is considered as an indicator of ultrahigh -pressure conditions (UHPM) . For example, pomegranate on the island of Otrow , Norway contains up to 19 mol.% Maj (3.19 formula units of Si ), which corresponds to a pressure of more than 12 GPa . ^{[6] [7]}