For someone's 75th birthday, what might serve as a symbolic or virtual diamond?

He has no use for actual diamonds. He won’t want a T-shirt, no matter what slogan is on it. He isn’t going to take a trip, and he doesn’t want a wall plaque or framed memento.

Still, I’d like to give him something special that makes 75 a little easier to take.

Something diamond-shaped? something that alludes to diamonds? or at least something of carbon?

For the latter, I suppose anything organic would do, but that seems a little crude.

I need ideas. Thank you.

Tags as I wrote them: birthdays, gifts, diamonds, 75th.