Haven't read the article because I'm lazy and I'm already based and conflict-mineralpilled on the subject so apologies if I'm already repeating what's mentioned in the article but when key figures of the Kimberly Process certification walk away from it (including one of the founders) and call it a bunch of bullshit (literally, in the words of Martin Rapoport) then the only conflict-free diamonds are the synthetic ones.
A decent article on the issue:
https://www.theguardian.com/sustainable-business/diamonds-blood-kimberley-process-mines-ethical
While we're on the topic of precious gems, don't think that Swarovski should ever be considered as an ethical alternative to diamonds because they only deserve consideration for where they rank in your shitlist:
More info: https://en.wikipedia.org/wiki/Swarovski
Also guess what other industry Swarovski is involved in? I'm sure it wasn't critical to the Nazi war effort or anything, right?