The issue centres around the social stigma of not having a diamond ring. Friends and family will ask what the stone is, and need to be educated. And no matter what you tell them, the perception will be that I was too cheap to buy her a real engagement ring. Nevermind the fact that I'm not actually saving any money, I'm just spending it somewhat more wisely.
It's actually a little bit of a stressful situation for me. I'm in the Royal Canadian Mint's MintChip Challenge, and I'm hoping to win some gold from the competition, so I can melt it down and make an engagement ring for her from that. In my eyes, that has more meaning behind it. Moreover, she's going on a trip with her sister to Prague & Rome in a month, a few days before our 7 year anniversary. Since she knows a proposal is coming, I was hoping to surprise her by showing up in Rome and proposing to her there. May not be the wisest way to spend my money, especially when I'm not exactly swimming in cash right now, but I felt it would be worth it for the memory and moment. To me, that's a better use for my money than some artificially-valued diamond. Seems like I'll have to scrap that plan and save more money for the ring she wants.
You can request Canadian diamonds at the jewelry store. My store had to overnight a collection in for us to look at, but it wasn't an issue for either of us.
Canada's diamond mines have labor and environmental standards to abide by and Canadian diamonds are laser inscribed with a goose logo and come with an extra certification being from Canada. De Beers does own 2 out of the 6 mines in Canada, but it does not have anything near a monopoly there.
Short version: do not do this, for it will rebound on you horribly.
I would be extremely hesitant about using that particular gambit.
This is as Micro as it gets. And why do you think oppurtunity cost is restricted to Macro?