It may surprise many geoscientists that some of the metamorphic rocks comprising parts of the Kokchetav Massif in Kazakhstan are, in terms carats/tonne, the most diamondiferous rocks yet recognized. Unfortunately, although the diamond crystals are abundant, they are exceedingly small, typically 5–25 3m, and the occurrence thus has no commercial value. In contrast, the scientific value of these rocks is enormous, as recrystallization of a supracrustal assemblage within the stability field of diamond at pressures of greater than 4.5 GPa requires burial to depths of at least 120 km, followed by uplift to crustal regimes. Tracing and understanding these processes...

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