Last evening's talk by Scott Ramsay was terrific, IMHO. It got me to thinking. I'd read someplace that diamonds can revert to their polymorph, graphite.
"Retrograde metamorphism is what makes diamonds so rare. Diamonds are made at great depths, and normal geologic processes that might bring diamonds to the surface are so slow that diamonds retrograde to graphite. Only the rapid eruptions that create kimberlites allow diamond to reach us without degrading."
It sounds bizarre, but: A snap-back in the diamond crystal lattice to graphite could extinguish any trace of diamonds, and thus, explain the missing alluvial diamonds in the eroded ore body. If so, those claims in the ocean will come up empty.
OK, a second consequence; If the transformation were partial, the graphite would color the partly transformed diamonds and they would turn brown, or sherry, topaz, champagne or whatever.
Third, the differences between the conditions of formation of lamproites and kimberlites could explain the differences in abundance, character and grade of the diamonds found therein, based at least in part on retrograde metamorphism.
There was no academic attribution for the quote above, but if there is evidence for it, then any of my hypotheses could be valid.
What do y'all think?
