Structural Transformations of Minerals in the Earth’s Mantle: the New High Pressure Polymorphous Modifications of Olivine and Wollastonite

Important results of studies of HP-minerals during 2018–2022 years are reviewed. The emphasis is made on the characterization of HP-polymorphous modifications of olivine (asimowite, poirierite) and wollastonite (breyite and davemaoite) discovered in this period. The structure of poirierite (ε-Mg2SiO4) contains a unique silicate chain Si3O9 with one tetrahedron in its period. Correspondingly, its structural formula is Mg2[SiO3]O, and its intergrowth with wadsleyite/ringwoodite in shocked chondrites supports the idea that olivine is transformed into ringwoodite through poirierite formation. The wollastonite (1T) at 8.9 GPa and its synthetic analogue CaGeO3 have similar unit cell parameters. The HP/HT data confirm the stability of the wollastonite polymorphs (1T, 2M, pseudowollastonite and synthetic analogue of breyite) within wide upper mantle depth range. The crystal structures and composition of new НР-minerals discovered in impact zones, meteorites, and inclusions in diamonds provide insight into a complex petrology of deep geospheres, which cannot be obtained in laboratory experiments.