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The carbon isotopic composition of diamond is reasonably well-known from measurements on hundreds of diamonds of known paragenesis. With very few exceptions, 5'^ C values of peridotite-suite diamonds are in the restricted range-2 to-9%<? pdb, whereas 5*^ C for eclogitic diamonds ranges from approximately+ 2 to-34% opdb (eg, Sobolev et al., 1979; Deines, 1980; Harris, 1987). In contrast to this large data set, few isotopic data have been published for either eclogitic or peridotitic mantle-derived graphite. Values of 5^^ C for primary graphites from peridotite xenoliths (-4.8 to-10.04% o; Kropotova and Fedorenko, 1970; Pearson et al., 1990; Schulze and Valley, in press) are similar to those from peridotitic diamonds. Existing carbon isotope data for graphite in mantle eclogites from Mir (Kropotova and Fedorenko, 1970), Roberts Victor (Deines et al., 1987), and Orapa (Deines et al., 1991) are, with one exception, in the" typical mantle range"(-3.98 to-8.7% opdb)-Graphite from a Schaffer, Wyoming kyanite eclogite (Schulze and Valley, in press) is unusually light, with 5*^ C=-14.31% o. An additional anomalous graphite analysis (5^^ C of-20.3% o) was reported by Deines et al.(1991) for a corundum-garnet-spinel assemblage of uncertain affinity, also from Orapa. To enlarge the data base for mantle-derived graphites, we present carbon isotope data for graphites from 23 eclogite xenoliths, from the Bellsbank and Jagersfontein kimberlites in South Africa and the Orapa and Letlhakane kimberlites in Botswana.

Most of our new data (Table 1) are normally distributed about a 5 ‘^ C value near-5 to-6% o. Interesting features in this new data set include …