Abstract:

The mineralogy of a diamond inclusion that is the corundum containing high chromium from Yuanshui, Hunan, China has been investigated. It is confirmed that the highest content of chromium in the chromiumcontained corundum may reach 19.31%. According to the EPMA analysis, the formula of the highchromium corundum is（Al1.683,Cr0.298,Fe0.010,Mn0.008,Ti0.004, Si0.001)2.004O3. Based on the Xray powder diffraction pattern and the method of full spectrum Rietveld fitted refinement, the crystallographic parameters were obtained as the following: R3c, a=04765 nm, c=1.3007 nm, Z=6, and the trivalent chromium and aluminum ions occupy the same crystalchemical position. Although the crystallographic parameters of the corundum suggest that it has regressed to the ordinary pressure state, the high chrome content implied that it had undergone a highpressure environment. Thus, it can be regarded as a kind of index mineral indicating a highpressure environment. The discovery of high Cr content of the Yuanshui corundum as a diamond inclusion suggested that the diamonds in this area were possibly from eclogite xenoliths.

Key words:  diamond, inclusion, corundum, Rietveld method, high pressure mineral