Microscale variations of δ13C and N content within a natural diamond with mixed-habit growth

The variations of carbon isotope composition and nitrogen content in a natural diamond with mixed octahedral and cuboid habit have been studied with the ion microprobe technique (SIMS). The systematic variations of δ13C and Nppm in continuous growth zones belonging to both octahedral and cubic sectors have been measured. In general the octahedral growth sector in comparison with the cuboid one is richer in nitrogen by 90–300 ppm and has a slightly heavier δ13C by 0.3–1.5‰. These data show that simultaneous mixed growth of cuboid and octahedral sectors in natural diamond entails little fractionation of carbon isotopes. The observed variations are most likely due to the different nature and kinetics of growth of natural cuboid and octahedral diamonds.