Already done, there were atmosphere-carbon diamonds on sale at Selfridges corner shop a couple of months back.
The report by Imperial College London Consultants, cited by Sky Diamond, highlights the environmental and climate costs of mining so-called precious stones:
http://www.imperial-consultants.co.uk/wp-content/uploads/202...
One more reason to ensure that synthetic diamonds cannot be identified or differentiated as such, given the high environmental impact of extracting that carbon allotrope from the ground.