The article says the diamond formed at that depth, but I assume the rock rose to a higher depth before it was extracted. I believe the deepest depth to which we have drilled is on the order of 10 km.
> The unexpected decrease in density, the greater porosity, and the unexpectedly high temperatures caused the rock to behave somewhat like a plastic, making drilling nearly impossible.
Temperature too high again? Have a long pause to make a little money from geothermal energy.
[1] https://news.stanford.edu/2019/05/23/lessons-south-korea-sol...