THE GROWTH HISTORY OF A SUBLITHOSPHERIC DIAMOND REVEALED BY 3D GROWTH ZONATION, INCLUSION MINERALOGY AND GEOBAROMETRY
The diamond is a faceted, 1.5 carat, D color, type IaB gem that passed through GIA’s grading infrastructure and was later purchased for research purposes. Its inclusions comprise olivine/ringwoodite (Mg, Fe)2SiO4, ferropericlase (Mg, Fe)O, enstatite (former bridgmanite, (Mg, Fe)SiO3, and other minor phases. The mineral assemblage is consistent with a meta-peridotitic host rock near the 660 km discontinuity at the base of the mantle transition zone. This depth is independently supported by elastic geobarometry for one of the ferropericlase inclusions.
A novel hyperspectral imaging technique has been applied to this specimen to examine its 3D spatial distribution of various photoluminescent defects. This otherwise invisible spectral and textural information provides a way to visualize the growth zonation of this diamond, as well as post-growth deformation. Taken together, the data provide a clearer picture of the formation conditions of this diamond and help place it in a broader geodynamic context.