A Mantle or Crustal Origin for Carbonado? Synthesis and Microanalytical Studies of Polycrystalline Diamond

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EAR-0073862Heaney/VicenziScientists have described carbonados as "the most enigmatic of all diamonds." They occur as pea-sized black nodules of fused diamond crystallites with relatively large void spaces that can account for more than 15% of the total volume. Some scientists have proposed a host of theories to account for their formation, some of which would dramatically influence our perception of the history and chemistry of the Earth if proved true. For example, some scientists believe that carbonados formed by a single massive meteorite impact in the late Archean, whereas others postulate that carbonados are an exotic style of diamond from the Earth's upper mantle. We intend to test these hypotheses by comparing carbonado textures and mineral inclusions with those in polycrystalline diamonds that crystallized deep within the earth and by meteorite impact. In addition, we will perform state-of-the-art imaging and geochemical analyses to explore for indicators that will unambiguously demonstrate the formation mechanisms of these unusual diamonds.