Fractionation of nitrogen isotopes in a synthetic diamond of mixed crystal habit

Nitrogen is the most abundant trace element in natural1 and meteoritic2 diamond and finds its way into synthetic diamonds during their manufacture3. In the first study of the isotopic composition in a synthetic diamond, we have found that nitrogen incorporated in a large (∼0.5 cm diameter) cubo-octahedron is isotopically fractionated between the zones of different crystal habit. The cubic {100} sector of the stone, which contains about half the concentration of nitrogen, is enriched by ∼4.5% in the heavy (15N) isotope of the element relative to the octahedral {111} growth region. This is the largest isotopic fractionation yet observed that can be attributed to the influence of crystal structure and demonstrates again the idiosyncratic behaviour of diamond with respect to nitrogen.