The presence of low concentrations of fullerenes has been reported from numerous terrestrial and meteoritic sources (Buseck, 2002). In a recent paper, Mossman et al. (2003) present mass spectra of carbonaceous substances using laser desorption ionization (LDI) and high-resolution electron-impact mass spectrometry. The authors confirm the presence of fullerenes in the Onaping Formation, Black Tuff from Sudbury, Ontario, but do not find fullerenes in carbon-rich shungite rocks from the Lake Onega region of Karelia, Russia. They conclude that the earlier observation of fullerenes in Karelian shungite may have been due to the intrusion of basic igneous rocks and attribute the absence of fullerenes in the four shungite samples they studied to the possible heterogeneity of shungites. However, the authors also argue: “Alternative explanations include the possibility that fullerenes do not occur in shungite, or that the discovery of fullerenes in shungite may have been an artifact of the analyses” (Mossman et al., 2003, p. 257). Moreover, the authors conclude that natural fullerenes appear to form exclusively in extraterrestrial samples. We disagree with these conclusions.
The first discovery of natural fullerenes in a geological sample was reported in shungite from Karelia (Buseck et al., 1992). Ebbesen et al. (1995) speculated that the fullerenes found in shungite were products of a localized event or were due to an experimental artifact; these arguments were challenged by Buseck and Tsipursky (1995). We subsequently reported the presence of fullerenes in shungite samples from Kondopoga (60 km southwest of Shunga), a different locality in Karelia (Parthasarathy et al., 1998). The sample was a bright shungite with ~10 wt% carbon. We used electron-impact ionization mass spectrometer (EIMS) in our experiments for the characterization of fullerenes. In contrast to LDI, which is known to create fullerenes under laser irradiance, EIMS is very safe for detecting fullerenes. The presence of fullerenes in Karelian shungite was confirmed independently by powder X-ray diffraction (XRD) and 13C-nuclear magnetic resonance (NMR) experiments (Parthasarathy et al., 1998). Hence, we do not agree with Mossman et al. (2003) that the fullerenes reported from shungite were due to experimental artifacts.
As has been pointed out by many people, Mossman et al. (2003) among them, Karelian shungite is highly heterogeneous. Fullerenes have only been found in the glassy variety of bright shungite (Buseck et al., 1992; Parthasarathy et al., 1998).
We have carried out a series of experiments exploring the presence of fullerenes in shungite from different areas of Karelia. We present here a typical mass spectra obtained from a dull shungite, in which the total carbon content was estimated to be 60 wt%. Figure 1 shows the mass spectrum of the carbonaceous matter extracted from a dull shungite and exhibits the absence of fullerene. Out of twelve Karelian shungite samples we found fullerenes in only three samples, all of which are bright shungite of glassy nature (Parthasarathy et al., 1998).
There is agreement that natural fullerenes are found in Cretaceous boundary layer samples (Heymann et al., 1994; Parthasarathy et al., 2002), meteorites (Becker et al., 1994), and Permian-Triassic boundary samples (Becker et al., 2001). However, Shimoyama and Yabuta (2002) could not find fullerenes in the Cretaceous-Tertiary boundary sediments at Kawarupu, Japan. We conclude that natural fullerenes exist in Karelian shungite and geological boundary samples. It is the choice of proper sampling that leads to success in finding the natural fullerenes in geological materials. However, the origin of fullerenes in geological materials is not yet understood. Buseck (2002) discussed the occurrence of natural fullerenes in a wide range of geological environments in a comprehensive review, indicating that the fullerenes are not restricted only to extraterrestrial samples. This conclusion is strongly supported not only by our studies on Karelian shungite, but also by the observation of fullerenes in solid bitumen from pillow lavas of Mitov (Jehliĉka et al., 2003).
We are grateful to Peter Buseck for very useful discussions. We thank B. Sreenivas and R. Srinivasan for providing the shungite samples. We thank V.P. Dimri, Director, National Geophysical Research Institute, for his encouragement and support.
