Synthesis of skeletal diamonds: Implications for microdiamond formation in orogenic belts

Figure 1. Secondary-electron scanning electron microscope images showing morphologies of (A) natural and (B, D, and E) synthetic diamonds. C: Energy-dispersive X-ray spectrum for diamond in B. Natural diamonds are separates from felsic gneiss of Kokchetav massif, Kazakhstan. Synthetic diamonds are crystallized from graphite 1 Mg(OH)2 systems and exhibit irregular skeletal morphology similar to that of diamonds from natural rocks. Diamond structure was confirmed by Raman spectroscopy (all synthesized diamonds are characterized by sharp Raman peak at 1332 6 3 cm21 similar to that shown in Fig. 3B). ABSTRACT Diamond was synthesized at high temperature and pressure in a Walker-style multianvil apparatus from various supercritical C-O-H–rich fluid compositional systems. Depending on the type and amount of impurities added to the system, diamonds of varying morphology and bearing solid oxide inclusions were found within the run product. These characteristics bear a striking resemblance to metamorphic microdiamonds recovered from the Kokchetav massif, Kazakhstan; these natural diamonds share morphological traits with our synthesized diamonds, and both the natural and synthesized diamonds contain similar solid oxide inclusions. Our data favor formation of Kokchetav diamonds via crystallization from a supercritical C-O-H fluid, rather than from carbonate or carbonatite melt, as others have suggested.