The aim of the project is to investigate the effect of iron on the chemical stability of calcium silicate perovskite (CaSiO3) in situ at conditions relevant to the Earth’s lowermost mantle using powder and single-crystal X-ray diffraction (scXRD) and Synchrotron Mössbauer Source (SMS) at pressures 90 – 130 GPa and temperatures 2200 K – 2800 K. To our knowledge, very little is known about the interaction of iron with CaSiO3 in lowermost mantle conditions, despite their anticipated co-existence in the mantle and Core-Mantle Boundary (CMB).