Some inclusions in diamonds formed at extremely high
pressures, near the base of the upper mantle. Although
they formed as single crystals, they became unstable
during their ascent in a mantle plume and have decomposed
into multiple phases. Figure 2 shows an inclusion
that formed as part of the Ca(Si,Ti)O3 perovskite solid
solution but subsequently broken down to form a large
colorless crystal of CaSiO3 and several small reddishbrown
crystals of CaTiO3. The Raman map allows us to
distinguish the two and confirm that no other phase is
present. Being able to demonstrate the presence of both
minerals is conclusive proof of the ultra-deep origin of
this sample: whilst CaSiO3 and CaTiO3 are both stable
over a wide range of pressures and temperatures, the
solid solution Ca(Si,Ti)O3 is only stable at pressures
>12 GPa at typical mantle temperatures.4