Breyite Inclusion in Diamond
Sublithospheric or “superdeep” diamonds are rare, estimated to make up only 1–3% of mined diamonds globally. They are recognized on the basis of their mineral inclusions. Breyite (CaSiO3) is one of the minerals sometimes encountered in this curious geological family of diamonds. Diamonds containing breyite are often interpreted to come from depths greater than 360 km, where the breyite would have initially had a high-pressure perovskite-type crystal structure. The perovskite-structured CaSiO3 would have changed to the breyite crystal structure in response to the drastic decrease in pressure during the diamond’s journey to the surface. Alternatively, it is theoretically possible that breyite could be trapped directly in a diamond at much shallower depths, say within 150–200 km, although such an occurrence within a known lithospheric diamond has yet to be encountered.
The breyite inclusion (see above) was recently observed in a 1.00 ct D-color type IIa diamond submitted to GIA’s New York laboratory. Raman spectroscopy was used to identify it as breyite. This large inclusion, 450 μm in its longest dimension, is colorless and transparent. A conspicuous healed fracture surrounds it, containing graphite (black) and smaller “sub-inclusions” of breyite that appear to emanate from the main inclusion. Based on this breyite inclusion, the diamond is suspected to be sublithospheric in origin
