Who makes them? What guy?
Two companies I know of are producing real gem-quality carbon crystals (diamonds).
Gemesis is the one whose products you're most likely to find in a jewelry store, with better color and clarity than pretty much anything ever dug up out of the ground. Yes, the diamonds they make are real diamonds, carbon crystals.
Apollo Diamond is by
far the more interesting company, however, in that they are producing single-crystal wafers. Wafers akin to the silicon wafers used to manufacture computer processors, processors which will soon be running so hot that they'll
melt silicon and silicon-on-insulator. Apollo Diamond's process allows them to precipitate specific amounts of helpful materials into their single-crystal diamond wafers making them even more desirable for this sort of manufacturing than even a pure diamond wafer would be. They've been slowly increasing the size of the wafers they grow, by growing them in a cone shape and slicing off the widest end for the seed for the next crystal - I'm not sure what size they're up to at the moment.