Introduction

Considerable interest centres on the Mantle constituting, as it does, more than half of the Earth by volume and by weight. Attention has been focussed on several problems, including the chemical composition, mineralogy, phase transitions and element partitioning in the Mantle, and the geophysical properties of seismicity, heat transfer by radiation, electrical conductivity and magnetism in the Earth. Many of these properties of the Earth's interior are influenced by the electronic structures of transition metal ions in Mantle minerals at elevated temperatures and pressures. Such effects are amenable to interpretation by crystal field theory based on optical spectral data for minerals measured at elevated temperatures and pressures.

In the Mantle, temperatures range up to several thousands of degrees Kelvin and pressures may exceed 100 GPa in the deep interior, attaining 136 GPa at the Core–Mantle boundary. In the past two decades, the optical spectra of several minerals and synthetic analogues have been measured at high pressures and elevated temperatures simulating conditions in the interior of the Earth. The results of many of these high P and T spectral measurements are reviewed in this chapter and applications of the spectral data are described to transition metal-bearing Mantle minerals.