Rhombohedral Structure: A New Phase of Pentlandite in Diamond Inclusion from Liaoning, China

Pentlandite inclusion presenting perfect crystal form with hexagonal symmetry in a diamond from Liaoning of China was confirmed based on electron microprobe analysis data.X-ray diffraction peaks obtained from single crystal diffractometer with CCD area detector demonstrate that pentlandite has rhombohedral and cubic structures by the powder method indexing procedure distinction and computation. Unit cell parameters of rhombohedral structure are as follows: a＝0.690 62 nm, c＝1.720 95 nm, V＝0.710 85 nm³ (hexagonal); a_R＝0.698 61 nm, α＝59.244 5°, and V＝0.236 95 nm³ (rhombohedral). The presence of rhombohedral phase in diamond inclusions reveals that the formation condition of the pentlandite in the mantle at ultrahigh-pressure and cubic phase is the results of phase transformation of the pentlandite inclusions in the atmospheric pressure since the diamond breaks.