Multiple core growth structure and nitrogen abundances of diamond crystals from Shandong and Liaoning kimberlite pipes, China

Diamond crystals from the Shandong and Liaoning kimberlites, China, display a distinct "seed-like" multiple core growth structure with multi-stage growth history. Cathodoluminescence and DiamondView images revealed that the core portion of the diamonds is occupied by a "seed-like" precipitated or smaller core which could be a resorbed early crystal formed by a cuboid growth mechanism. At the boundary between the core portion and the octahedral layers, the nitrogen concentration drops abruptly to ∼1 ppm from a few hundreds of ppm in the core portion, suggesting a fundamental change in geochemical growth environments in the mantle. This is associated with a switch in zoning trends in δ ¹³C from outward increasing to outward decreasing values, confirming that a change in growth conditions occurred.