Comparison of carbon in shungite rocks to other natural carbons: An X-ray and TEM study

The shungites of Karelia (Russia) form a large, diverse group of black Prec ambrian rocks, all of which contain an intriguing type of poorly crystallin e carbon. Wide differences of opinion exist about its structural state and its relation to carbon from other geological environments and origins. We u sed a variety of measurement techniques to determine the structural feature s of the carbon in shungite samples and to relate them to other natural sou rces of carbon. Although there is a wide range of types of shungite rocks, it appears as if the structure of their carbon is similar throughout in res pect to high-resolution transmission electron microscopy (HRTEM) images, an d electron and X-ray diffraction patterns. Other samples whose carbon is in distinguishable using these techniques include those from the Erickson gold mine (Canada), the Sovetskaya gold mine (Russia), and the Sudbury impact s tructure (Ontario). Carbon samples from different localities of the Shunga district are characterized by containing curved layers, similar to samples from natural and synthetic cokes. The HRTEM images and nanodiffraction patt erns of shungites suggest that some 3-dimensional closed shells occur but, more commonly, there are fractions of such shells or regions of structure t hat art: highly disordered into bent stacks of graphene layers. (C) 2001 El sevier Science Ltd. All rights reserved.