• electron microscopy
• highly reduced phases
• low oxygen fugacity
• Mriya lamproite pipe

This thesis reviews the geological setting of the Mriya lamproite pipe within the Ukrainian Shield and focuses on the mineralogical characterization of some highly reduced phases and associated silicates found in inclusions within corundum grains from this locality. These phases, which form under conditions of low oxygen fugacity, may provide valuable insights into deep Earth processes and their surface occurrences. The study is complemented by comparative analyses with two other significant geological sites — Mount Carmel (Israel) and the Luobusa ophiolite (Tibet, China) — which also feature reduced mineral phases, with the aim to contribute for a broader understanding of their formation and geological significance.

Advanced microscopic and analytical techniques, including Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), Energy-Dispersive X-ray Spectroscopy (EDS), and 3D Electron Diffraction (3DED), were used to study the mineral phases. This characterization revealed structural features and chemical compositions typical of minerals rather unusual on the Earth surface, such as wassonite, kushiroite and hibonite, and also revealed the presence of potentially new mineral phases.

These findings can contribute to the understanding of mantle redox conditions and metasomatic processes occurring in the deep mantle. Additionally, this study briefly addresses the economic implications of these reduced phases, particularly in the context of diamond formation and their potential applications in materials science.