The Formation of Polycrystalline Diamond: A Microstructural and Microanalytical Study of Carbonado

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9706143 Heaney This project will investigate the isotopic structure of carbonado, a variety of polycrystalline diamond. It is hypothesized that carbonado did not form in the upper mantle, but crystallized from preexisting organic carbon. The PI's will examine carbonado samples from Brazil and the Central African Republic. They will address the following questions: (1) what is the source of the carbon? (2) What is the microstructural evidence for meteoritic shock? (3) Did the REE-phosphates form by fissiogenic processes? (4) Did these carbonados crystallize as part of a single event or process? A variety of microanalytical techniques will be used. Electron microprobe and TEM will be used to investigate shock textures. SIMS will be used to determine C isotopes and REE ratios.