In prismatine granulite from Waldheim/Saxony, I found a perovskite crystal with corroded nanodiamonds. Has anyone had an explanation for this unusual paragenesis?
Remark to the nanodiamonds (ND): The ND is formed from microdiamonds during the fast ascent of the supercritical fluid from mantel deeps into the level of the prismatine growth. Here start the ND-to-carbon onion transformation process (Cebik et al. (2013)). This process takes place at temperatures >1000°C. An onion-like skin of graphite surrounds the nanodiamonds now. The majority of the microdiamonds are converted to layers of sp2-carbon. This process makes the usually strong diamond peak at 1332 cm-1 disappear, and the G band increases significantly. Note the Raman signal of nanodiamonds is generally very weak. Often we also observe a down-shift of the asymmetrically broadened diamond peak to about 1320 cm-1.
Cebik, J., McDonough, J.K., Peerally, F., Medrano, R., Neitzel, I., Gogotsi, Y., Osswald, S. (2013) Raman spectroscopy study of the nanodiamond-to-carbon onion transformation. Nanotechnology 24, 205703, 1-10
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