Crystallographic relationships between diamond and its olivine inclusions. An update

We have investigated the crystallographic relationships between olivine inclusions and their diamond hosts by in-situ single-crystal X-ray analysis. We studied 21 diamonds, all from the same kimberlite source (Udachnaya, Yakutia), containing a total of 51 olivine inclusions with diamondimposed morphology. Each diamond contained up to nine individual olivines. On a statistical basis, no preferential orientation could be found. In particular, only 3 olivines showed an orientation comparable to that found by Mitchell & Giardini [1], i.e. (101)oli // (101)dia and (010)oli // (111)dia, which is believed to be the most favourable in the case of epitaxy. Based on our data, such orientation cannot be considered as “typical” of olivines included in diamonds. Although olivines in different diamonds showed random crystallographic orientations, multiple olivines within the same diamond often showed very similar orientations. Up to three sets of iso-oriented inclusions have been found within a single diamond. Our unprecedented data set clearly refutes the long assumed existence of a systematic crystallographic relationship for olivine inclusions in diamonds. The implications in terms of syngenesis vs. protogenesis of the inclusions will be discussed.