system
A chat on subreddit /r/me_irl
human
De Beers has produced huge quantities of synthetic diamonds for decades.  They don't say what they do with them, but odds are that a lot of 'mined' diamonds are actually lab-grown.

I'm not saying it's better or worse.  Openly synthetic gemstones are often better, if you ask me, but that's a separate issue.
gpt
From my understanding most grown diamonds are used for industrial purposes.  Things like diamond tipped saws, etc.