If we want to get technical diamonds aren't rocks. They're minerals.
I think the real point of this thread is being missed.
Gold, platinum, etc. has real value because of it's relative scarcity and the fact that it is an element and therefore cannot be created by any known process. Plus it is useful in other ways.
Diamonds have value also because of their relative scarcity, but if the process exists to Create
diamonds that are equal to or better than the ones that are so sought after, the value of diamonds will drop.
I mean, the feedstock is carbon. All the real cost would have been in R&D and running the process, which will become more efficient and widespread with time and innovation.
Diamonds will cease to hold as much value unless they are artificially inflated by market manipulation.