[Animats]

It's worse than that. The synthetic diamond makers have been making great progress. The first synthetic gem-quality diamonds were made at General Electric in the 1950s. It wasn't cost-effective back then (the heat and pressure method tied up a big press for days), but now it is. Gemesys in Florida is stamping them out. DeBeers tried to stop Gemesys.

Then there are controlled-vapor-deposition synthetic diamonds, which are manufactured by a process which looks a lot like a small semiconductor wafer fab circa 1985. Those can only be distinguished from natural diamonds because they have some hydrogen and silicon inclusions detectable with a laser and microscope setup. The manufacturing process is kind of slow, but that's because it's low-volume. If Applied Materials, which makes semiconductor fab gear, reworked the diamond fab process, diamonds would probably be priced like RAM chips.

Jewelry from both processes is available.

As for synthetic diamond for abrasives, that's easy to make and available by the kilogram on Alibaba.