Unusual paired pattern of radiohaloes on a diamond crystal from Guaniamo (Venezuela)

An octahedral diamond crystal from Guaniamo, Venezuela shows a multitude of round radiocolouration spots that indicate a remarkable formation history. Spots always occur in pairs, with similar spacing and intensity ratio between the two spots of each pair. We interpret this pattern to be the result of long-term irradiation of the stone emanating from a multitude of radioactive point sources. At some point during the irradiation, the stone must have experienced a translational movement which shifted it ca. 50 μm relative to the adjacent material [i.e., the (111) crystal face was a fault plane], after which irradiation continued. The Neoproterozoic age of the Guaniamo kimberlites and the high degree of radiation damage suggest that both of the two irradiation periods lasted over hundreds of millions of years. This interpretation is supported by results of He-irradiation experiments.