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The identification of syngenetic inclusions in diamond (i.e. inclusions of minerals that crystallized at the same time and by the same genesis as their host) has long been of paramount importance in diamond studies. However, the widespread assumption that many or most inclusions in diamonds are syngenetic is based on qualitative morphological criteria and few direct measurements. In order to provide statistically significant information on inclusion–host genetic relations for at least one kimberlite, we have determined the crystallographic orientations of 43 olivine inclusions with diamond-imposed morphology, a feature generally interpreted to indicate syngenesis, in 20 diamonds from the Udachnaya kimberlite (Siberia). Our unprecedented large data set indicates no overall preferred orientation of these olivines in diamond. However, multiple inclusions within a single diamond frequently exhibit similar orientations, implying that they were derived from original single monocrystals. Therefore, regardless of the possible chemical re-equilibration during diamond-forming processes, at least some of the olivines may have existed prior to the diamond (i.e. they are protogenetic). Our results imply that a diamond-imposed morphology alone cannot be considered as unequivocal proof of syngenicity of mineral inclusions in diamonds

Calcite crystals were nucleated and grown from supersaturated aqueous solutions in the presence of variable concentrations of lithium. The diagram of supersaturation vs [Li+]/[Ca2+] concentration ratio (“morphodrome”) shows a continuous habit variation, from the dominant {011̄1} rhombohedron (at low [Li+]/[Ca2+] ratio) to the dominant {0001} form (at high [Li+]/[Ca2+] ratio). The morphological change is interpreted in terms of two-dimensional layers having the structure of the monoclinic Li2CO3 crystal which are epitaxially adsorbed on the restructured {0001} form of calcite. Hence, even if {0001} is a K form (in the sense of Hartman-Perdok), the corresponding surface behaves like a F form, growing layer by layer from low to high supersaturation values.

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