Iron and Its Compounds in the Earth’s Core: New Data and Ideas

Iron is the most abundant chemical element of the Earth’s core and makes up more than 85 wt % of its mass, with the remaining ~15% thought to be Ni and some lighter elements: Si, C, S, O, and H. The paper presents and analyzes newly acquired data on the transformations of iron and its compounds at high temperature and pressure, corresponding to those in the Earth’s core, and discusses the structural types of mineralogically possible polymorphic modifications of iron and its compounds in the deep geospheres in the Earth’s core. New data on changes in the electronic structure of iron atoms at high pressure are presented. Preexisting concepts are expanded and new ideas are suggested for the forms of concentration of chemical elements at ultra-high temperature and pressure. It is concluded that current understanding of the characteristics and properties of the Earth’s mantle and core are not only based on data provided by geological and geophysical methods but are also specified with the application of micro-mineralogical and crystallographic approaches.