This conflicts with what I think I know about the occurrence of diamonds. For the most part diamonds are formed just below the surface in melts rich in dissolv

This conflicts with what I think I know about the occurrence of diamonds. For the most part diamonds are formed just below the surface in melts rich in dissolved carbon dioxide. These materials rise through the crust through very narrow pipes and explode when the carbon dioxide comes out of solution at the surface. These explosions form the bell shaped bodies that are mined for diamonds. Because of the phase behavior of carbon dioxide rich melts, and because the diamond grade just below the bell is very low, diamonds seem to be formed in the high pressure streams of carbon dioxide released when the temperature declines and the confining pressure is released at the surface. Perhaps there are "seed" crystals formed much deeper and such a crystal formed the nucleus for this diamond. From this popular article it is not possible to determine at what depth the water crystal formed. Conceivably it could have formed in the stream of carbon dioxide at the surface.