X-ray Diffraction Studies on Graphites from Dharwar Craton

We report here., the results of powder x-ray diffraction studies on six graphite samples from the Archaean metasedimentary rocks of Dharwar craton, with the motivation of correlating the graphitization process of carbonaceous matter during metamorphism with metamorphic grade. Our studies show that interplanar spacing d(002) and crystallinity L_c(002) for all the studied samples are very close to that of well crystallized graphite.

The observed decrease in full width at half maximum (FWHM) of the (002) diffraction peak from 0.20 to 0.102 Å. increase in crystallite size, L_c(002) from 408 to 800 Å and graphitizing degree from 86 to 362 indicate different metamorphic grades. Our results indicate that the rocks from Hampapura are of low metamorphic grade and those from Arjun Bettahalli are highly metamorphosed. The peak metamorphic temperatures of metasedimentary rocks are estimated to be around 600±50°C. The temperature estimates based on graphite crystallinity studies and the temperatures estimated by silicate mineral geothermometry studies of the coexisting mineral assemblages were found to be consistent.